Contents

Contents
1. Botanical Classification
Classification of Genus Citrus
Criteria for Citrus Classification
Different Classification
Subgenus Eucitrus (10 Species)
Subgenus 2. Papeda (6 Species)
Subgenera 1. Archicitrus (5 Sections, 98 Species)
Subgenera 2. Meta Citrus (3 Sections, 46 Species)
Others of Somewhat Doubtful Classification
Information on Important Citrus Fruits
Subgenus Fucitrus (Edible Citrus Fruits)
Acid Group
Citrus Medica Linn. (Citron)
Citrus Lemon Burm (Lemon)
Citrus Aurantifolia Swingle (Acid Lime)
Citrus Latifolia Tanaka (Tahiti or Persian Lime)
Citrus Limettioides Tanaka (Sweet Lime)
Citrus Jambhiri Lush (Rough Lemon; Jambiri)
Citrus Limetta Risso (Limetta of the Mediterranean)
Citrus Karna Raff (Kharna Khatta)
Citrus Limonia Osbeck (Rangpur Lime)
Citrus Pennivesiculata Tanaka (Gajanimma)
Orange Group
Citrus Aurantium Linn (Sour, Bigarade or Soville Orange)
Citrus Sinensis Osbeck (Sweet Orange)
Citrus Myrtifolia Raffinesque
Citrus Bergemia Risso (Bargmot Orange)
Citrus Natsudaidai Hayata
Pumelo-Grapefruit Group
Mandarin Group
Citrus Reticulate Blance (loose skinned orange or Santra of India)
Citrus Unshiu M (Satsuma Mandarin)
Citrus Deliciosa Tenore
Citrus Nobilis Loureio (King Mandarin)
Citrus Reshni Tanaka (Spice Mandarin)
Citrus Medurensis Lou (Calamondin)
Citrus Madaraspatana Tanaka
Subgenus Papeda : (Inedible Citrus Fruits)
Eupapeda Citrus
Citrus Macroptera (Metanewsian Papeda)
Papeda Citrus
Citrus Ichangensis
Citrus Iatipes (Khasi Papeda)
Kumquats
Fortunella Margarita Swingle (Nagami or Oval Kumquat)
Fortunella Japonica Swingle (Marumi or Round Kumquat)
Fortunella Crassiflora Swingle (Meiwa Kumquat)
Fortunella Bindsii Swingle (Hong Kong wild Kumquat)
Poncirus Trifoliata L. (Trifoliate Orange)
Citrus Relatives
Aegle Marmelos Linn. (Bael)
Feronia Limonia (Linn) Swingle (Wood apple)

2. Citrus Cultivation
Sweet Oranges
Citrus Sinensis Osbeck
Batavian
Hamlin
Jaffa
Malta Blood Red
Mosambi
Pineapple
Sathgudi
Shamouti
Valencia Late
Washington Navel Oranges
Mandarin Oranges
Citrus Reticulata B.
Calamondin (Citrus Madurensis Lou)
Cleopatra (Spice Tangerine) C. reshni T.
Coorg Orange
Dancy Tangerine
Desi Mandarin (Pathankot)
Khasi Orange
King Mandarin
Kinnow Mandarin
Nagpur Santra
Satsuma Orange (C. unshiu M.)
Temple Mandarin
Lemon C. limon Burm
Eureka Lemon
Lisbon Lemon
Lucknowseedless
Hill Lemon (Galgal) C. pseudolimon Tanaka
Malta Lemon
Meyer Lemon
Napali Oblong
Villafranca
Lime
Acid Lime (Citrus aurantifolia Swingle)
Tahiti (Persian) Lime (C latifolia Tanaka)
Rangpur Lime (Citrus Limonia Osbeck)
Sweet Lime (Citrus Limettioides Tanaka)
Pummelo (C.Grandis Osbeck)
Nagpur (Chakotra)
Grapefruit (C.Paradisi Macf)
Duncan
Foster
Marsh Seedless
Ruby
Shaharanpur Special
Thompson (Pink Marsh)
Citrus Hybrids
Inter Generic Hybrids
Hybrids of Poncirus
Citranges
Citrangequats (Cit)rus O(range) Kum(quats)
Citrangedins (cit)rus O(range)×Calomon (din)
Citrangors
Cleitranges
Citrumelos
Hybrids of Fortunella
Procimequat (Pro(to)C(itrus×L)imequat.
(Fortunella japomica×C.aurantifolia, Cv.—Mexican)×F.hindsii.
Limequats (C. aurantifolia×F. japonica)
Orangequats. (C. reticulata Cv. satsuma×F. japoncia×F. morgarita Cv. meiwa)
Hybrids of Genus Eremocitrus
Intrangeneric Hybrids

3. Citrus Fruits
Sweet Orange
Climate
Soil
Cultivars
Mosambi
Blood Red Malta
Sathgudi
Pineapple
Washington Navel
Jaffa
Shamouti
Valencia Late
Hamlin
Batavian
Propagation
Raising of Seedlings for Rootstock
Budding
Planting
Manure and Fertilizers
Irrigation
Interculture and Intercropping
Training and Pruning
Bahar Treatment
Fruit Drop
Physiological Fruit Drop
Control Measures
Pathological Fruit Drop
Control Measures
Harvesting
Yield
Post Harvesting Handling and Storage

4. Mandarin
Uses
Climate
Soil
Varieties
Nagpur Santra
Khasi Orange (Mandarin)
Coorg Orange
Desi Mandarin (Pathankot)
Other Varieties
Propagation
Manure and Fertilizers
Yield
Post Harvest Handling and Storage

5. Kinnow Mandarin
Uses
Climate
Soil
Propagation
Planting
Manures and Fertilizers
Irrigation
Interculture and Intercropping
Flowering and Fruiting
Harvesting
Yield
Post Harvest Handling and Storage

6. Sour Lime
Uses
Climate
Soil
Types/Varieties of Lime
Kagzi Lime
Chakradhar Lime
Rangpur Lime (Citrus limonia Osbeck)
Taheti (Persian) Lime (C. latifolia Tanaka)
Propagation
Raising of Seedlings
Planting
Manure and Fertilizers
Irrigation
Interculture and Intercropping
Training and Pruning
Flowering and Fruiting
Harvesting
Postharvest Handling and Storage

7. Sweet Lime
Uses
Climate
Soil
Varieties
Mitha Chikna
Propagation
Planting
Manures and Fertilizers
Irrigation
Training and Pruning
Flowering and Fruiting
Harvesting
Yield
Handling and Storage

8. Lemon
Uses
Climate
Soil
Varieties
Eureka
Lisbon Lemon
Villafranca
Lucknow Seedless
Nepali Oblong
Baramasi
Kagzi Kalam
Hill Lemon. (Galgal) C. pseudolemon Tanaka
Meyer Lemon
Pat Lemon
Italian Lemon
Rajamundary Lemon
European Lemon
Ponderosa Lemon or Japanese Lemon
Malta Lemon
Propagation
Planting
Irrigation
Manure and Fertilizers
Training and Pruning
Improvement in Yield
Harvesting
Yield
Post Harvest Handling and Storage

9. Grapefruit
Uses
Climate
Soil
Varieties
Marsh Feedless
Duncan
Foster
Saharanpur Special
Ruby
Thompson (Pink Marsh)
Triumph
Propagation
Planting
Irrigation
Training and Pruning
Flowering and Fruiting
Harvesting
Yield
Post-harvest Handling and Storage

10. Pummelo
Uses
Climate
Soil
Varieties
Propagation
Planting
Cultural Practices
Harvesting and Yield
Insect-pests of Citrus Fruits
Lemon Butterfly (Papilio demoleus Linn)
Control Measures
Citrus Leaf Miner (Phylloenistis Citrella Stainton)
Control Measures
Citrus Psylla (Diaphornia Citri Kuwayma)
Control Measures
Whiteflies
Control Measures
Control Measures
Aphids
Control Measures
Mites
Control Measures
Scale Insects
Control Measures
Nematodes
Control Measures
Stem and Bark Borers (Indarbela Tetraonis Moore and I. qudrinotata Walker)
Control Measures
Fruit Sucking Moths (Ophideres spp).
Control Measures
Fruit Flies (Daccus spp).
Diseases of Citrus Fruits
Gummosis (Photophthora spp, Diplodia Natalensis Pole Evans)
Control Measures
Ganoderma Root Rot (Ganoderma Lucidum Karst)
Control Measures
Pink Disease (Pellicularia Salmonicolour Dastur)
Control Measures
Powdery Mildew (Acrosporium Tingitaninum Subr).
Control Measures
Anthracnose (Colletotrichum Gloeosporioides and Gloeosporium Limethicolum Clausen)
Control Measures
Twig Blight (Diplodia and Fusarium spp.)
Control Measures
Citrus Canker (Xanthomanas Citri Dowsan)
Control Measures
Tristeza Virus Disease (Corium Vialoris)
Control Measures
Xyloporosis
Control Measures
Psorosis
Control Measures
Exocortis or Scalybutt
Control Measures
Citrus Greening
Control Measures
Dendrophthoe
Control Measures
Fruit Cracking
Control Measures
Citrus Decline
Control Measures
Granulation
Control Measures
Fruit Drop
Control Measures
Alternate Bearing
Control Measures

11. Citrus Fruit Breeding
Aims of Citrus Breeding
Related to Fruit Characters
Related to Tree Characters
Related to Rootstocks
Problems in Citrus Breeding
Time
Polyembryony
Sterility
Breeding Method
Introduction
Selection
Hybridization
Mutation Breeding
Choice of the Procedure
Cytogenetics
Blossom Biology in Citrus
Blooming Period
Flower Bud Differentiation
Flower Bud Development
Inflorescence
Sex Ratio
Anthesis
Dehiscence
Stigma Receptivity
Storage, Longevity and Fertility of Pollen
Pollen Germination
Pollination and Fecundation
Fruit Development
Technique of Hybridization
Structure of the Citrus Flower
Calyx
Corolla
Stamens
Pistil
Selection of Parents
Selection of Seed Parent Trees, Branches and Flowers
Bagging the Flowers
Emasculation
Pollination
Fruit Set

12. Suitable Climate
Influence of Climatic Factors
Temperature
Relative Humidity
Rainfall
Winds
Altitude
Climatic Requirements of Different Citrus Species
Sweet Oranges (Citrus Sinensis Osbseck)
Mandrin Oranges (Citrus Reticulata Blanco)
Acid Lime (Citrus Aurantifolia Swingle)
Sweet Lime (Citrus Limettioides Tanaka)
Lemon (Citrus Limon B)
Grapefruit (Citrus Paradisi Macf)
Pummelo (Citrus Grandis Osbeck)
Climate in Different Regions of India

13. Type of Soil
Water Drainage
Depth of the Soil
Nature of the Subsoil
Soil-reaction
Salts
Type and Fertility of the Soil
Soils Requirement of Different Citrus Species
Citrus Soils of India
Citrus Soils of Flsewhere
Work Done in India
Citrus Breeding in U.S.A.
Tangelos (Tangerine × Grapefruit)
Citranges (Poncirus Trifoliata × Citrus Sinensis)
Citrangequats (Citrange × Kumquat)
Limequats (Mexican Lime × Kumquat)
Hybrid acid Citrus fruit
Mandarin Types
Citrus Breeding in U.S.S.R.
Citrus Breeding in Other Countries
New Approaches in Citrus Breeding in India

14. Making an Orchard
Selection Of Site
Spacing
Preparation of the Site
Layout
Selection of Varieties
Digging and Filling of Pits
Planting Season
Planting
Care of Young Plants

15. Cultivation of an Orchad
History
Cultivation
Greenhouse
Orchad House and its Management
Composts, Potting Methods, and Containers
Bark Preparation
Feeding of Orchad Plants
Outdoor Cultivation of Orchads
Growing Orchads in Outdoor Beds
Vegetative Propagation
Raising of Orchads from Seeds
Care of Seedling
Shoot Tip or Meristem Culture
Differentiation of Flower Buds and Induction of Flowering
Resting
Method of Hybridisation
Storing Pollen
Procedure for Pollination
After Pollination
Diseases and Pests
Control Measures for Fungal Diseases
Viral Diseases and their Control
Insect Pests and their Control

16. Propagation of Citrus Fruits
Seed Propagation
Seed storage
Seed Bed
Sowing Time
Sowing
Germination
Shade
Nursery Bed
Care of the Young Seedlings
Asexual Propagation
Budding
Preparation of Stock Seedling
Collection of Budwood
Storage of Budwood
Method of Operation
Height of the Budding
Lopping
Care of Young Budlings in the Nursery
Digging of Budlings
Transporting
Budwood Certification Programmes
Cuttings
Layering
Grafting
Top-Working
Purchasing of Seedlings or Budlings
Care of Plants on Arrival from the Nursery
Propagation of Different Citrus Species
Bud Variation
Causes of Bud Variations
Classification or Variations
Significance of Bud Variation
Bud Selection
Bud Selection Methods
Nucellar Embryony
Origin and Development of Nucellar Embryos
Factors Affecting the Polyembryony
Identification
Inheritance of Nuclear Embryony
Nucelear Emorbyony in Citrus Species and Cultivars
Strongly Polyembryonic
Weekly Polyembryonic
Number of Embryos Per Seed
Number of Nucelear Seedlings Per Seed
Horticultural Significance
Significance of Nucelear Embryony in Citrus Breeding
Nucelear Embryony and Heterozygosis
Drawback of Nucelear Seedlings
Performance of Nucelear Lines
In Vitro Culture of Nucelear Embryos

17. Budded Roots
Qualities of a Good Rootstock
Citrus Rootstocks in India
Citrus Rootstocks of the World
Rootstock Trials in India
Punjab
Uttar Pradesh
Assam
Andhra Pradesh
Maharashtra
Karnataka
Tamil Nadu
Characteristics of Rootstocks
Cleopatra Mandarin: Citrus Reshni T.
Troyer Citrange
Citrus Sinensis × Poncirus Trifoliata
Swingle Citrumelo
Duncan Grapefruit × Trifoliate Orange
Stock and Scion Relationships in Citrus
Effect of Root stock on Vigour of the Scion
Effect on Precocity
Effect on Productivity and Yield
Effect on Fruit Size, Colour and Quality
Effect on Winter Hardiness
Effect on Nutrition
Effect on Disease Resistance
Effect of the Scion on Rootstock
Effect of Interstocks
CITRUS ROOTSTOCK PROBLEMS
Stionic Failures
Viruses
Diseases
Nematodes
Salts

18. Cutting of Weak/Neglected Parts
Pruning of Young and Pre-bearing Plants
Pruning Bearing Trees
Pruning Older Trees
Pruning Neglected Trees
Pruning Overgrown Trees
Hedging
Root Pruning
Pruning Time
Wound Protection
Pruning Different Citrus Species
Pruning Problems

19. Soil Inspection for Citrus Family
Soil Tillage
Different Soil Management Practices

20. Inter Cultivation
Choice of Intercrops in India
Intercropping in Other Countries

21. Nutrition for Citrus World
Mineral Nutrition
Nitrogen
Phosphorus
Potassium
Calcium
Magnesium
Sulphur
Zinc
Iron
Copper
Manganese
Boron
Molybdenum
Combined Nutritional Sprays
Factors Governing the Nutrition
Nutrient Elements Balance
Manuring and Fertilization
Manuring of Young and Pre-bearing Trees
Manuring Bearing Trees
Time of Application
Methods of Application
Foliar Analysis
Soil Vs. Foliar Analysis
The Concept of Foliar Analysis
Factors Affecting Mineral Composition of Leaves
Methods of Leaf Sampling
Preliminary Survey of Orchard and Selection of Initial Sampling Technique
Methods of Analysis
Leaf Analysis Standards
Interpretation of the Leaf Standards of Different Elements

22. Control Irrigation
Irrigation Requirement of Citrus Trees
Time and Frequency of Irrigation
Quality of Irrigation Water
Systems of Irrigation
Basin System
Furrow System
Flood Irrigation System
Check System
Sprinkler Irrigation
Advantages
Disadvantages
Drip- or Trickle-irrigation
Advantages
Disadvantages
Pitcher System
Sub-surface Irrigation
Irrigation to Young and Pre-Bearing Trees
Irrigation to Bearing Trees

23. Unwanted Weed Removal
Control
Weed Control in Nurseries
Weed Control in the Main Field
Herbicidal Effects
Phytotoxic Effects
Other Effects

24. Proper Harvesting of Citrus
Picking Time
Methods of Picking
Handling
Grading
Packing
Marketing

25. Oil of Bergamot

26. Oil of Lemon

27. Oil of Mandarin

28. Oil of Orange

29. Study of Orange Essential Oils
Analysis by Infrared Spectroscopy

30. Study of Orange Essential Oils
Chemical Modifications During Aging

31. Citrus Carotenoids (I) The Structure of Citranaxanthin, a New Carotenoid Ketone
Experimental
Isolation of Citranaxanthin I
Anal. Calcd.
Alkali Cleavage of Citra anaxanthin (I).
Reduction of Citranaxanthin
Citranaxanthin (I)
Anal. Caled.

32. Citrus Carotenoids (II) The Structure of Reticulataxanthin

33. Factors Direct Fruit Variety
Climatic Factors
Temperature
Water
Nutritional Factors
Nitrogen
Phosphorus
Potassium
Magnesium
Manganese
Copper
Boron
Rootstock Effects
Fruit Size
Colour of Rind
Juice
Total Soluble Solids
Total Acidity
Ascorbic Acid Content

34. Post Harvesting of Citrus Fruits
Degreening
Pre-harvest Treatment
Post-harvest Application
Storage
Waxing
Polyethylene Covers
Growth Regulators
Cold Storage
Controlling Moulds in Storage

35. New Problems for Citrus Family
Alternate Bearing
Factors Affecting Alternate Bearing
Control
Resting Treatment
Choice of Bahar
Granulation
Analogy of Granulation
Physico-chemical Characteristics of Granulated Fruits
Incidence and Progress of Granulation
Factors Affecting Granulation
Humidity
Temperature
Light
Tree age
Tree health
Tree Vigour
Tree Aspect
Tree Variation
Fruit Size
Rootstock
Varietal Susceptibility
Control Measures
Irrigation
Effect of Time Sprays
Effect of Growth Regulators
Nutritional Sprays
Citrus Decline
Symptoms
Factors Responsible for Citrus Decline
Soil Factors
Nutritional Factors
Rootstock Factors
Orchard Management Factors
Insect-pests
Nematodes
Fungal Diseases
Viruses
Control Measures
Fruit Drop
Retarding or Inhibiting Factors
Accelerating or Initiating Factors
Temperature
Water
Insect Pests and Diseases
Physiological Factors
Nitrogen
Carbohydrates
Auxins
Embryo Development
Control of Fruit Drop
Mandarins
Sweet Oranges
Grapefruit
Lemons

36. Use of Plant Growth Regulators
2,4-Dichlorophenoxy Acetic Acid (2,4-D)
2,4,5-Trichlorophenoxyacetic Acid (2,4,5-T)
Napthalene Acetic Acid (NAA)
Gibberellins
Cytokinins
Growth Retardants
Ethylene
Limitations

37. Serious Diseases of Citrus
Diseases Caused by Fungi
Gummosis
Symptoms
Etiology and Spread of Disease
Varietal Susceptibility
Control Measures
Preventive Measures
Curative Measures
Diplodia Gummosis
Symptoms
Spread
Control
Ganoderma Root Rot
Symptoms
Control
Pink disease
Symptoms
Control
Powdery Mildew
Symptoms
Etiology and Spread
Control
Felt Disease
Symptoms
Etiology and Spread
Varietal Susceptibility
Control
Anthracnose
Symptoms
Etiology and Spread
Control Measures
Scab
Symptoms
Etiology and Spread
Varietal Susceptibility
Control
Dry Root-rot
Symptoms
Etiology
Control
Armillariella Root-rot
Symptoms
Control
Sooty Mould
Symptoms
Damage
Etoilogy and Spread
Control
Melanose
Symptoms
Etiology and Spread
Control
Twig Blight
Etiology
Symptoms
Control
Leaf Fall and Fruit-rot
Symptoms
Etiology
Control
Sphaeropsis Knots
Limb Breakage
Greasy Spot
Nursery Diseases
Diseases Caused by Bacteria
Citrus Canker
Symptoms
Etiology and Spread
Varietal Resistance
Control
Citrus Blast
Bacterial Root Rot
Diseases Caused by Viruses
Diseases Affecting Certain Stionic Combinations
Tristeza or Quick Decline
Symptoms
Etiology
Transmission of the Virus
Varietal Susceptibility
Control
Saving the Existing Infected Orchards
Avoiding Losses in New Citrus Plantings
Xyloporosis
Symptoms
Virus Diseases Occurring Irrespective of Rootstocks
Psorosis
Symptoms
Etiology
Control
Stubborn Disease
Symptoms
Etiology
Diseases Caused by Viroids
Exocortis or Scalybutt
Other Miscellaneous Virus Diseases
Budunion Crease
Citrus Mosaic
Infectious Variegation
Yellow-Corky Veins
Blastomania
Leaf-curl-disease
Other Virus-Like Disorders
Creeping Stem
Bark Eruptions
Woody Galls
Young Tree Decline
Gummy Pitting
Tatter Leaf— Citrange Stunt Complex
Citrus Mosaic, Navel Infections Mottling and Natsudaidai dwarf
Citrus Greening
Symptoms
Etiology
Transmission
Varietal Susceptibility
Control
Phanerogamic Parasites
Dendrophthoe (Loranthus)
Cassytha
Physiological Disorders
Foam Disease
Symptoms
Cause
Fruit Splitting
Symptoms
Cause
Control
Endoxerosis
Symptoms
Cause
Control
Creasing (Puffiness)
Rough Fruit Disorder
Market for Storage Diseases
Penicillium Moulds
Alternaria Rot
Black Core Rot
Diplodia-Stem-end Rot
Aspergillus Rot
Miscellaneous Diseases

38. Important Pests of Citrus
Introduction
Root Pests
Stem and Trunk Pests
Borers
Chloridolum Alemene Thomson
Monohanmus Versteegi Nitzema (Trunk Borer)
Stein and Bark Borers (Indarbela Spp.)
Damage by Borers
Control
Foliage Pests
Lemon Butterfly (Papilo Demoleus Linn.)
Papilionidae : Lepidoptera.
Distribution
Host Plants
Life History
Damage
Control
Citrus Leaf-Miner: (Phyllocnistis Citrelia Stainton) (Phyllecnistidae: Lepidoptera).
Distribution
Host Plants
Life History
Damage
Control
Citrus Psylla: Diaphornia Citri Kuwayama
Distribution
Host Plants
Life-history
Damage
Control
Whiteflies (Aleurocanthus Spp, Dialeurodes Spp)
Distribution
Host Plants
Life History
Damage
Control
Weevils: (Myllocerus Discolor BOH)
Mealy Bugs : Pseudocoecus Spp (Pseudococcidae : Hemiptera)
Distribution
Host Plants
Life History
Damage
Control
Aphids: Hemiptera Aphididae
Distribution
Host Plants
Life History
Damage
Control
Thrips: (Scirtothrips spp, Heliothrips spp)
Distribution
Host Plants
Damage
Life History
Control
Scale Insects: (Coccidoe: Homoptera)
Damage
Armoured Scales
Unarmoured or Soft Scales
Spread
Control
Mites: (Textranychidae: Acarina)
Distribution
Life History
Damage
Citrus Rust Mite: Phyllocoptruta Oleivorus Ashm
Six-spotted Mite : Tetranychus Sexmaculatus Riley
Control
Minor Pests
Hairy Caterpillars Euprotctis Fraterna M
The Citrus Leaf-roller (Psorosticha Zizyphi Staintor)
Orange Hair Streak: (Taraucus Theophrastus)
A Grass Hopper : Poekilocerus Pictus Fab
Cricket: Braehytrypes Portentosus Light
Longhorn Bettle: Oberea Mangalorensis
Flower Pests
Citrus Flower Moth : Prays Citri Milliers
Cacoecia Epicyrta Meyrick
Blossom Midge Sayneura Citri G & P
Fruit Pests
Fruit Sucking Moths (Noctudidae : Lepidoptera)
Calpe Emarginata
Distribution
Host Plants
Life History
Damage
Control
Fruit Flies
Distribution
Host Plants
Life History
Damage
Control
Fruit Sucking Bugs
Distribution and Host Plants
Life History
Damage
Control
Citrus Rind Borer: Prays Endocarpi Meyrick.
General Control Measures

39. Nematodes of Citrus
Citrus Root Nematode
Tylenchulus Semipenetrans Cobb. 1913
Host Range
Control Measures
Cultural Control
Biological Control
Resistant Rootstocks
Reniform Nematode (Rotylenchulus Reimformis)
Burrowing Nematode (Radopholus Similies)
The Lesion Nematode (Pratylenchus Coffeae)
Root-knot Nematode (Meloidogyne Africane)
The Lance Nematode (Hoplolaimus Indicus)
Poncirus
Fortunella (Kumquats)
Citrus

Sample Chapters

Botanical Classification

Citrus fruits are members of the Rutaceae family   which contain more than a thousand species mostly found in the tropical region of Africa   South East Asia and Australia.

Generally the three related genera Poncirus   Fortunella and Citrus are

Classification of Genus Citrus

Classification of citrus fruits is a very problematic one   which awaits still a perfect solution   agreeable to one and all. Many scholars have made attempts to group the numerous species of Citrus in some sort of orderly arrangement   but failed in their attempts. Says Most of these classifications   instead of elucidating the problems with which they dealt   have only made them more complicated. Each classification had its own limitations and drawbacks.

Early attempts by Europeans have resulted in very simple classifications   limiting the entire group of citrus fruits to about a half  a  dozen species in one genus. Such classifications not only grouped   such diverse forms as limes and citrons in one species   but give a species standing to different forms   closely related to each other and left out entirely a large number of fruits unknown to them. They mainly depended upon the herbarium specimens of citrus fruits. They had no acquaintance with the places where citrus fruits originated. The various problems faced by the systematic pomologists are enumerated below:

Instead of taking the citrus fruits as they found growing at present   many scholars have based it on imagination   how they have been thousands of years ago.

Very few scholars had a personal knowledge of the whole region in which the species have originated and being grown   many have seen only those which are grown in the West.

Many of the characteristics on which classifications are commonly based   are not constant within the species   as new forms seem to occur more frequently.

The high frequency of bud sports or mutations also cause inconvenience in the classification.

The species of genus citrus being easily crossable within and without   a number of interspecific and intergeneric hybrids increased. But these hybrids   the products of two or more heterozygous parents   tend to segregate in the next generation   thus the taxanomist is at loss to classify them. Though many scholars have exonerated the hybrids as species   however   Singh accepted them as valid species   by questioning the validity of giving a species status to Prunus domestica  a hexoploid.

There is no general agreement about what constitutes the species. According to earlier botanists   a plant should be given a species rank on the basis of occurrence of its wild forms. Others stressed that a species should represent a definite unit   sufficiently different with any another unit   notwithstanding the presence of its wild forms   history and different geographical distribution.

Variation in popular names as well as in botanical names makes the problem more complicated.

Diversity of forms in genus Citrus and their localisation in the world add to the chaotic condition. Some of the citrus fruits are so localised in certain parts that they are hardly known outside their native homes.

Criteria for Citrus Classification

Taxonomists have employed different criteria for classifying citrus fruits. The important characters   on which classification was based are elucidated below:

Plant characters: Hardness to cold   height   habit   mode of branching   foliage   nature of thorns   roundness of branches   pubescence.

 Leaf characters: Shape   size   thickness   apex   margin   colour   vines   wings   articulation   aroma of crushed leaf   and pubescence of leaf.

Floral characters: Sex   solitary or crowded   size of peduncle   pedicel   size of flower   pubescence   colour   shape of calyx   division of sepals   stamens free on united   nature of anthers   ovary size   shape   colour   style size   nature of stigma   fragrance of flowers and nature of inflorescence.

Fruit characters:

External characters: colour   shape   size   surface   base of calyx   areole   persistency of style.

Internal character: Nature of rind (thickness   firmness and adherence)   density of oil glands  colour of glandular layers   taste of mesocarp   number and size of carpels   pulp  colour and texture   size and shape of juice vesicles   closely or loosely packed   arising from dorsal or radial side of carpellary wall   presence or absence of acrid oil   axis   hallow or solid   juice taste   quality amount and flavour   sugar and acid content   seeds  number   size   shape. colour cotyledons   colour   nature of embryo   whether monoembryonic or polyembryonic   number of embryos.

Miscellaneous characters Fruiting season   quality rank   general and horticultural importance and uses.

Different Classification

Though more than a dozen of scholars   notably in U.S.A. and Japan have attempted to classify citrus fruits   only the works of Swingle and Tanaka are noteworthy. Tanaka was the erstwhile student of Swingle and after leaving Swingle   he did much independent work and made a valuable contribution to the Citrus classification. After Swingle and Tanaka. In India scientists have classified the citrus fruits of Assam. Of Late Singh by taking the advantage of Swingle  s and Tanaka  s treatments has attempted to classify citrus fruits and evolved a key for the identification of different citrus fruits.

The basic difference between Swingle and Tanaka is their independent outlook about what constitutes the species. Swingle followed the traditional views about the species rigidly and rejected most forms   considered to be of hybrid origin and lack of wild forms. He called such of those species of doubtful validity   which may be a natural species of comparatively recent origin or may be a chance hybrid or sport as   satellite species. His classification was considered as a conservative type and he was considered as a   lumper  .

On the other hand   Tanaka  s treatment of 1954 is elaborative. He reiterates that a species should represent a definite unit sufficiently different from another unit. He has given a species rank to every form showing a slight difference. By such a liberal attitude and approach he has arrived to a figure of 145 species   while Swingle recognized only 16 species and 8 botanical varieties of genus Citrus. Thus they represent two extremities in Citrus classification.

         

Workers made a critical study of both Swingles and Tanaka s treatments of citrus fruits. He observed that former  s approach to the problem is not comprehensive   (i) that it does not adequately cover the forms of horticultural importance   (ii) that numerous ancient oriental forms of citrus for instance   Indian   Japanese and Chinese   were ignored   (iii) that the approach denies species standing to many ancient   well known and distinctive forms   for example   Rough lemon   Rangpur lime   Palestine sweet lime   Satsuma mandarin etc.   (iv) that treatment of certain distinctive forms led to complication   speculation   besides being cumbersome   for example   Rough lemon was said to be a hybrid of Citrus limon   Palestine sweet lime as a hybrid of C. aurantifolia   King mandarin as a hybrid between mandarin and sweet orange   (v) that consistency is wanting (a) separate species standing is sanctioned for obviously closely related forms   for instance pummelo and grapefruit   sweet and sour orange   (b) at the same time separate species standing is denied to forms   which obviously differ much more   for instance   all mandarins in one species   all true limes in one species and the lemon like forms all in one species.

While in the case of Tanaka  s system   others observed (i) that the system contains an excessive number of species   for example   35 species with mandarin group alone: (ii) that it is hard to justify the number of species as differences so minor as scarcely detectable are considered for giving species standing   (iii) that numerous cultigens  some of doubtful validity were also granted species rank   (iv) that species standing was given to certain natural hybrids or forms of doubtful justification   (v) that approach appears to be unnecessarily complex and detailed.

We have studied some of the little  known citrus fruits of India during 1959  62 and recorded his observations and opinions. Hodgson observed wide variations in Rough lemon (C. jambheri   Lush.) and amilbed (C. megalaxycorpa.)   moderate variations in attani (C. regulosa Tanaka)   considerable variations in Rangpur lime (C. limonia   Tanaka)   galgal (C. pseudolimon   Tanaka)   Karna (C. Karna   Raf)   gajanimma (C. pennivesiculata   Tanaka)   and limited variations in sweet lime (C. limettioides   Tanaka). Several distinct forms of the above species were recognised with respect to tree   leaf   flowering   bearing and fruit characters. Most of the forms described by Bhattacharya and Dutta (2) were found identical to one or the other species studied.

Scientists felt that species standing was justified in the cases of Rangpur lime   Rough lemon   sweet lime   galgal   Kharna Khatta   Kichili   gajanimma   attani   Indian wild orange and Khasi papeda   but   were doubtful of the justification of granting species rank to adajamir of Assam   amilbed   sadaphal and sat Kara. They opined it would be justified if adajamir of Assam is treated as botanical variety of gajanimma of South India C. pennivesiculata. var assamensis and sat Kara as botanical variety of C. macroptera  C. macropetera var. annamensis.

Of Late Singh felt a need for a compromise between Swingle s and Tanaka s classification of Citrus. With this approach he has accepted citrus forms of hybrid origin as valid species. He has accepted the subgenus Papeda of Swingle and has divided the subgenus Eucitrus into 8 groups   which correspond closely to the 7 sections of Tanaka. The major deviation from Tanaka  s classification is that citron and true lemon have been put under two separate but related groups. Tanaka has accommodated these under sub  section Citriodes and Limonoides   under section Citrophorum. In the present treatment lemons have been split under two groups. The lemon  citron of the Bojoura type (C. limonimedica Lush) which resembles the citrons in the bushy habit   serrations and rumpling of leaves   persistent style   flower characters and continuous flowering habit   have been grouped   along with citrons and the true lemons (C. limon Burn) of the tree type with solid core   flowering once a year   and thin   caducous style   have been put under the Limoid group along with Rough lemon (C. jambhiri lush) and Hill lemon or Galgal (C. pseudolimon Tanaka). This has facilitated the relationship between the last 3 species.

Information on Important Citrus fruits

Subgenus Fucitrus (Edible Citrus Fruits)

Includes all the cultivated citrus fruits. Pulp vesicles are free from acid droplets   filled with pleasantly acid   subacid or sweet juice. Petioles wingless or slightly winged   stamens cohering in bundles.

The following are the important fruits in Eucitrus:

Acid Group

Citrus Medica Linn. (Citron)

Commonly considered to be indigenous to India. Singh reports the distribution of many types of citron all over India. Probably citron is the first citrus fruits to reach Europe. Romans found it growing in Media and Pesia   hence the name Citrus medica. Jews called it Etrog and made use in their rituals. It is mainly grown for its peel. Citron is most sensitive to frost.

A shrub or small tree   with a short indistinct trunk and short   thick   irregular   thorny branches   thorns short   sharp   leaves large   not articulated   oval  oblong with serrate margin   rounded apex   dark green above   lighter beneath   petioles without wings   flowers large   axillarly   in compact clusters of 3  10   often unisexual   calyx small   cupped   corolla white within   tinged with purple on the outside   stamens short   40  45 in number   pistil large   ovary 9  12 loculed or more   fruit lemon yellow   large   oblong   rough or warty   sometimes ridged   apex blunt  pointed   rind thick   white except for the outer coloured rind   core hallow   pulp sparse   juice scant   acid or sweet   juice sacs small   slender   seeds oval   plump   numerous   monoembryonic.

Citrus Lemon Burm (Lemon)

Origin of the lemon is a mystery. Most of the authors agree on one point that South Eastern Asia is its natural home   but dispute whether India can exclusively claim as its home. Since no wild forms of lemon were found in India   Bonavia concluded that it originated in Malaya   quoting Rumphius  saying that Malayans call all citrus fruits by lemon and that Malaya may probably be the home of lemon. Hayes stated that lemon is commonly said to be indigenous to India. Hodgson states that the lemon must have originated in the eastern Himalayan region of India and adjoining areas   where citron also originated   for natural hybrids   with citron and lemon characters are found abundantly there. Dutta proclaim that in the light of the above   it is not unnatural that the primeal forest of Assam where lemons of various kinds are found even today to grow in a wild state   might be a probable home of lemon. However   it is upto the future research workers to decide upon this subject   till such time. India   especially Assam may tentatively be said the home of lemon. Singh says that true lemons are not indigenous to India and the cultivars like Lisbon and Eureka are introductions in India. Lemon is sensitive to frost.

Small to medium trees with spreading growth habit   with long   round or angular thorny branches   leaves evergreen   alternate   medium to large   lanceolate   sharp  pointed with sub  serrate margin   light green   petioles wingless   flowers medium sized   solitary in axils   on distinct peduncles   purple when young   sometimes staminate by reduction   calyx persistent   corella large   white in side   purplish outside   stamens 20  26   apparently free or sometimes united in bundles   pistil densely dotted with oil glands   ovary elevated on a prominent disc   7  10 loculed   fruit ripens at all seasons   ovoid or oblong   and pointed at both base and apex   light yellow   surface smooth or rough   rind thin   yellow when ripe   flesh light coloured   juice abundant and acid   juice sacs long and pointed   core solid seeds few   small   oval   quite smooth   pointed at the micropylar end   embryo white   polyembryonic.

Citrus Aurantifolia Swingle (Acid Lime)

Includes   Egyptian   Indian and Mexican limes. Tanaka says it is a native of Malayan peninsula   while Hume says it is native to India and South  eastern Asia. It is widely distributed and naturalized in the tropics. Lime and lemon are usually confused and thought one and the same   though both are distinct from each other. In habit of growth   in the winged petioles   in the clustered blossoms   in the flavour of the fruit   in their immunity from citrus scab   the limes are in a class by themselves and quite different from the lemons.

A shrub or small tree of straggling habit   with small   stiff   interlocking or drooping thorny branches   thorns small   sharp   numerous   young branches light green   becoming darker with age   leaves small   elliptic oval   orange like (hence the name) glossy green   margin slightly indented   petioles narrowly winged (similar to sweet orange)   flowers  small   axillary in clusters of 3  10   bisexual   faintly pink in the bud   but fades easily   calyx 4  5   pointed   petals 4  5 fleshy   stamens small 20  25   united into bundles   ovary about 10  loculed   fruits small   greenish yellow   round to oval   frequently popellate   peel very thin   paper like (hence Kagzi from Kagaj meaning paper) and auromatic   pulp greenish   acid   juice sacs small   slender   pointed   seeds small   oval   pointed   highly polyembryonic.

Citrus Latifolia Tanaka (Tahiti or Persian Lime)

It is a native of South Pacific. Botanically it closely resembles aurantifolia but physiologically it is quite different. It is as hardy as lemon. It is a triploid. It is more resistant to pests   diseases and unfavourable conditions in general.

A large vigorous tree with fewer   but thicker thorns   leaves much larger and thicker   somewhat different in form   and much darker green   flowers large and faintly coloured in the bud fading rapidly   fruits solitary or in clusters   large fruits often mistaken for small lemons   seeds few or lacking   apparently monoembryonic.

Citrus Limettioides Tanaka (Sweet Lime)

It is indigenous to India. An important rootstock in the near East and grown to some extent for the non  acid fruit. Tender to frost.

Medium to large spreading tree   irregular in growth habit   with fairly long slender thorns and new growth colourless   leaves medium in size   pale green and characteristically somewhat rolled or cupped   petiole  s wing margined rather than winged as in other limes   flowers moderately large and non  coloured   fruits medium in size   globose to ellipsoid   generally with low   flat papilla   rind thin with distinct aroma   surface some times very smooth   flesh pale yellow   juice abundant   flavour insipid   seeds medium in size   cotyledons white   highly polyembryonic.

Citrus Jambhiri Lush (Rough Lemon   Jambiri)

Tanaka found this fruit scarce in eastern India   though Bonavia collected it in the United Provinces. Dutta found at least six distinct forms of jambhiri in Assam and believed Assam as native place of jambhiri. Singh reports unlimited variation in the types of Rough lemon found in India. As such it can safely be concluded that Rough lemon is indigenous to India. It is one of the world  s principal rootstocks. It is fairly sensitive to frost.

Tree is medium to large with spreading growth habit   less spiny than lemon   leaves smaller   round apex   paler in colour   marginal serration fainter   flowers smaller   faintly coloured in the bud   petals less deeply coloured   pistil sparsely granular dotted   fruit lemon brown   very different in form   round   compressed with fleshy apical papilla   strongly developed cavity surrounding papilla   rough irregular surface adherence of rind fairly loose and core open at maturity   pulp yellow   seeds   numerous   small   highly polyembryonic.

Citrus Limetta Risso (Limetta of the Mediterranean)

Small to medium round  topped tree of less vigour and more compact growth habit   fruit small round shaped or depressed   lemon yellow   acid less at maturity. Its most distinctive features are the truncate apex   with a strongly depressed circular furrow in the centre of which is a prominent fleshy papilla or nipple   Polyembryonic.

There appear to be two forms   which are identical with the exception of the colour factor (flowers and new growth). The form in which the colour is developed   is commonly referred to as a sweet lemon and appears to be the   lumia   of the Mediterranean. The form which exhibits no colour development is often referred to as sweet lime and appears to be the limetta of the Mediterranean. Since they are both non  acid and differ only in the colour factor   it seems best to assign them to the same species.

Citrus Karna Raff (Kharna Khatta)

It is indigenous to India   it exhibits characters suggestive of the lemon   and Rough lemon or possibly sour orange also. The leaves and flowers of this species are similar to those of Rough lemon   but are larger in size and the petiolar wing is more prominent. As a root stock it is widely used in India.

Medium to large tree of upright spreading growth habit   spines thicker and larger than lemon   new flush fairly coloured   leaves large lemon like   but broader and darker green   petioles longer and more prominently winged   flowers large   tinged with red   fruit orange coloured   medium to large   oval with well developed apical papilla   surface rough and irregular   rind thick   adherence strong   core open at maturity   pulp orange   juice plenty   but sour   moderately seedy   cotyledons white: moderately polyembryonic.

Citrus Cultivation

The nomenclature and distinction of the cultivars of Citrus is as problematic and confused as the classification of genus Citrus. The problem of distinguishing the different clones or clonal varieties   on the basis of what constitutes a clone   seems to be a simple one. However   accidental mixtures will frequently occur   making it difficult to distinguish   unless the variety in question is sufficiently distinct from others to be easily recognisable. Further   no variety is likely to remain entirely static and unchanged over long periods   no matter even if it is perpetuated vegetatively.

The frequency of bud variations in Citrus seems to be high. Unless these bud variations are eliminated   the cultivar will not remain pure and may become a heterogenous mixture leading to confusion.

Environmental factors manifest variation with respect to period of blooming   yield potential etc.   by which the plants within a cultivar show variation from each other   demanding a separate identity.

Clones propagated by buds taken from a selected individual are called bud strains. However   the progeny of these bud strains from different trees of the same variety often exhibit differences   detectable only by growing them in considerable number in close proximity   adding further confusion to nomenclature.

The presence of numerous hybrids also adds to the confusion of nomenclature. For the present it is best to segregate them based on their parentage like citranges (Trifoliate orange × sweet orange) tangelos (mandarin orange×pumelo) etc.

The local names also contribute their might to the chaos in the nomenclature and distinction of cultivars of Citrus. Descriptions of some important cultivars of Citrus are furnished in the following pages.

Sweet Oranges

Citrus Sinensis Osbeck

The cultivars of sweet orange (tight skinned orange) may be separated into several easily recognizable groups   but within these groups there are large number of cultivars so similar that they cannot be readily distinguished.

Hume has arranged the cultivars of sweet orange into four groups : (i) Spanish oranges   (ii) Mediterranean oranges (iii) Blood oranges and (iv) Naval oranges.

While Webber classified the cultivars into three large groups:

(i) Those with normal fruits (ii) those with abnormal or navel fruits and (iii) the Blood oranges with red or red streaked pulp.

The most important cultivars of sweet oranges   cultivated on a commercial scale in India are Malta Blood Red and Pineapple in Punjab   Mosambi in Western India   Sathgudi and Batavian in South India.

 

Batavian

The name suggests that it has come from Batavia.

The cultivar can hardly be distinguished from Sathgudi except in rind colour   which is light yellowish green   usually with pale yellow patches on the green rind in the case of Batavian. In Sathgudi axis is solid while in Batavian it is hollow. It is inferior to Sathgudi in quality.

This is mainly grown in coastal districts of Andhra Pradesh.

Hamlin

It originated in Florida and named after the owner of the grove in which it was found in 1879.

Fruit medium in size   deep greenish yellow early in season   changing to orange  red with full maturity   apex rounded and very slightly scarred   base smooth   rounded   rind very smooth   bright   thin   segments   11  12   uneven in size   flesh deep orange  yellow   juice abundant   acidity and sugars well lended   flavour excellent   seeds usually 1  5   but many fruits are seedless.

It is an early variety grown in Punjab   Haryana   Uttar Pradesh etc.

Jaffa

It belongs to Mediterranean group of Hume and to normal fruit group of Webber. It is from Palestine.

Fruit medium to large   orange  yellow to orange red   globose to ellipsoid   apex rounded   base rounded   rind smooth   finely pitted   medium thick   oil glands medium in size   numerous   segments 9  12   flesh yellow   fine grained   pulp melting   acidity and sweetness normal and well blended   flavour rich   quality excellent   light orange   core small   seeds few 9  10.

It is a mid season variety   cultivated in Punjab   Haryana   and Uttar Pradesh.

Malta Blood Red

Blood oranges   so called due to the presence of red colour or red streaks in the pulp   have come from Mediterranean region.

The tree dwarfish   compact   distinct in growth habit   abundant foliage   small oval leaves   rounded   almost wingless petioles. The fruit is medium to large in size   round or slightly long   cadmium  yellow   rind usually thin   tight and glossy   pulp streaked red early in the season and full red colour when ripe   fine grained   melting   sweet and acidity well blended   juice abundant   T.S.S. 10 per cent rich in flavour and excellent in quality.

This is a mid  season variety   mainly under cultivation in Punjab   Haryana   Uttar Pradesh   Madhya Pradesh and West Bengal.

Mosambi

The name has its origin from Mozambique   thence it was introduced into India.

Fruits small to medium   subglobose or elongated   surface smooth   with longitudinal furrows and the apex marked with a circular ring (areole)   rind is marigold   thin   tight more difficult to peel   pulp apricot yellow   juice not plentiful   though sweet   sometimes almost insipid   owing to lack of flavour and inadequate blending of acidity with sugars   contain 18  25 seeds. The colour of the rind remains green or yellowish  green under tropical conditions.

It is an early variety   cultivated mainly in Western India in states like Maharashtra   Gujarat.

Pineapple

Pineapple comes under the Mediterranean oranges of Hume and normal fruit group of Webber. The Pineapple originated as a seedling in Citra   Florida. Due to its similarity of its flavour to that of pineapple it was named as Pineapple. It is one of the leading sweet oranges under cultivation in United States.

The fruit is sub  globose to round   medium sized   deep orange coloured when ripe   rind thin   tight   smooth   bright and glossy   finely pitted   apex rounded or slightly depressed or scarred   pulp is orange yellow   abundant   melting   flavour rich   acidity and sweetness well blended   T.S.S. 9.5 per cent   excellent quality   seeds 13 to 24.

Mid season variety cultivated in Punjab   Haryana   Uttar Pradesh etc.

Sathgudi

Sathgudi is also called as Chinee orange. The name Sathgudi owes its origin to a place Sathgur in Tamil Nadu.

Fruit almost spherical   small to large   smooth surface   attractively orange coloured when fully mature   base and apex evenly rounded   rind thin with little rag   semi  glossy and finely pitted. Pulp uniformly strawcolured   juicy   flavour excellent   seeds few to many 12  20   segments 10  12.

In most places   the fruit does not develop proper colour as it is picked before fully ripe. It is seen in the market from October to February. Sathgudi is mainly cultivated in southern districts of Andhra Pradesh and Tamil Nadu.

Shamouti

It was placed under normal fruit group by Webber and not described by Hume. It originated in Palestine during the early part of 19th century   probably as a bud sport or bud mutation from the Bellady orange of Palestine and was introduced into U.S.A. in 1920.

Fruit ellipsoid   size large   orange to deep orange   surface finely pitted   but relatively smooth   base evenly rounded   rind thick   firm and solid   axis small   solid or semi  hollow   segments usually 10  12   pulp light orange   firm   juice medium abundant   flavour sweet and rich   seedless.

It is a mid to late season variety   grown mainly in Palestine.

Valencia Late

Hume grouped it under Mediterranean oranges while Webber placed it under normal fruits. Though this fruit was introduced from Europe to other countries its origin is not fully known. Lee and Scott evidently indicated China as the most probable place of origin   thence it was introduced into Europe very early by Portuguese or Spanish voyagers.

Fruits medium to large   round or slightly oval   deep golden orange   apex rounded   slightly flattened   scarred   base smooth   rounded   rind thin   smooth   tough   axis medium   solid or semisolid   sections 9  12   pulp orange coloured   juice abundant   melting   acidity and sweetness well blended   excellent flavour and quality   seeds few 5  6.

It is a late varity grown in Punjab.

Washington Navel Oranges

It is grouped under Navel oranges. It is an important commercial orange of California. It originated near Bahia   Brazil in the early part of the 19th century and was first imported from Brazil in 1870 into Washington   from whence it obtained the name.

Fruit globose to obovoid or elipsoid   size large   orange or orange  yellow   apex slightly protruded or broadly nippled   navel medium to large   enclosed to broadly open   sometimes protruding   base rounded or somewhat flattened   rind smooth   tough   leathery   medium thick   segments usually 9  11   well defined   flesh rather coarse   deep orange  yellow   juice abundant   pulp melting   acidity and sweetness well blended   flavour rich and quality excellent   seedless.

It is an early varity   found promising at Kodur   Andhra Pradesh.

Mandarin Oranges

Citrus Reticulata B.

Loose  skinned oranges   belonging to species Citrus reticulata Blanco are commonly designated as mandarians. Though mandarin and tangerine are names used more or less interchangeably to designate the whole group   tangerine is applied more strictly to those varieties producing deep orange or scarlet fruits. The differences between these two groups are very slight   the main visible difference being the colour of the fruit   usually considered varietal in magnitude. As such from the horticultural standpoint   the Dancy and Beauty tangerins can be called as mandarins. This is easily said than done because these two names got firmly established in the world markets and cannot be easily erased.

Inspite of their close relationship and having many characters in common   the mandarin oranges can easily be separated into rather distinct  groups   in fact certain investigators have proposed to recognize these groups as distinct species. As such   King orange was given a name   Citrus nobilis   and Satsuma oranges are named as C. unshtu while Swingle considered them as natural varieties of mandarin oranges. Webber has separated the mandarin oranges into (i) King group (ii) Satsuma group   (iii) Mandarin group   (iv) Tangerine group   (v) Mandarin  lime group and finally (vi) Mitis group. However   till the taxonomic investigations are completed   it seems advisable to retain the name mandarin as group name to all the loose  skinned oranges.

The most important mandarin in India   undoubtedly is the Santra (Citrus reticulata) which includes varieties such as Nagpur santra   Coorg Santra   and Khasi orange.

Calamondin (Citrus Madurensis Lou)

Although Swingle recognised it as a valid species in 1914   he did not accord species rank. While Tanaka placed with the loose skinned orange group   but retained its specific rank as C. mittis. It is very cold resistant for a true citrus fruit   as hardy as Satsuma. It has been mentioned as a promising hardy stock in Texas   for the lime.

Tree tall   upright   columnar   rather bushy and dense   slightly thorny   leaves broadly oval   lighter green below   petioles short   narrowly winged. Fruit colour orange to deep orange   surface smooth and glossy   very finely pitted   shape oblate to spherical   size small   base flattened   even or very slightly depressed   apex markedly flattened   and depressed   rind thin   loose   easily separable when ripe   tender and sweet   oil abundant   odour pleasant   segments 7  10   pulp orange coloured   juicy   acid   seeds few 0.5.

Clementine (Algerian Tangerine)

It is a tangerin. According to Trabut it is probably an accidental hybrid of the mandarin and the sour orange and originated in a garden in Algeria. Since it was found as a chance seedling   the percentage is not known and believed simply to be a variant within the mandarin group. It was first introduced into the United States in 1909.

Tree size medium   spreading   nearly thornless   somewhat willowy   foliage dense   leaves dark green above and lighter green below   lanceolate   petioles medium in length   slightly winged if any   fruit colour deep orangered   surface smooth and glossy   slightly pitted   shape globose to elliptical   size medium   base evenly rounded to slightly necked   basal area with radiating furrows   apex depressed   rind thick   loose   axis large and hollow   segments 8  12   adherence slight   pulp deep orange   tender melting   quality and flavour excellent   seeds for 3  6.

It is an early variety.

Cleopatra (Spice Tangerine) C. reshni T.

Tanaka considers it as originated in China   as it is identical with the Ponki   a variety of Chinese origin   which is used in Japan and U.S.A. as a root stock. The Cleopatra was introduced into Florida from Jamaica.

Tree thornless   with dense top   upright but inclined to be willowy   leaves small   fruits produced singly or in bunches   fruit colour dark orange red   shape oblate   flattened at both ends   irregular in outline   size small   rind rough thin   loosely attached   segments 12  15 small   flesh orange   coarse grained   juice abundant   acidity and sweetness normal   quality good   seedy   about 20 or more.

Coorg Orange

It is the most important commercial variety in South India   particularly grown on large scale in Coorg and Wynad tracts.

The trees are very vigorous and upright with compact foliage   sparingly spinous. Fruits medium to large   bright orange in colour   oblate to globose in shape   finely papillate and winkled   glossy   base necked or depressed with glandular ribs extending through the collar   rind thin to medium   soft   adherence slight   easily peeled   segments 9  11   rag little   pulp vesicles uniformly coloured   texture fine and tender   flavour good   juice abundant   deep chrome in colour   acidity and sweetness well blended when ripe. Seeds 14  30   matures a little later than Nagpur Santra.

Dancy Tangerine

In the United States the Dancy is the best known and most highly prized of all the mandarin oranges. Dancy originated from a seedling in Florida.

Tree large   nearly thornless   upright in growth   foliage moderately dense   leaves broadly lanceolate   large   potioles medium   very slightly winged. Fruit colour deep orange red to scarlet   surface smooth glossy   in age becoming bumpy and irregularly furrowed   shape oblate to pyriform   size medium   base sometimes evenly rounded   but mainly slightly or markedly necked   apex broadly depressed   rind thin   leathery   rough   loose   and easily separable   axis large   hollow   segments 10 14   rag little   pulp dark orange   melting   flavour rich   quality excellent   seeds 6 12.

It is a late variety.

Desi Mandarin (Pathankot)

This variety is mainly grown in the Punjab hills. It seems to have originated as a seedling.

The tree is large   with semi upright growth habit   and compact foliage and spineless.

Fruit ovoid to sub  globose   colour uniformly Cadimum   surface pitted   semi  glossy and finely wrinkled   base short  necked and furrowed   rind medium   firmness soft   adherence   slight   segments 7  10   rag little   pulp vesicles uniformly genista coloured   texture fine and tender   flavour fair   quite juicy   deep chrome  coloured   slightly acidic   seeds few 3  7.

Khasi Orange

It is the chief commercial variety of Assam   and has many local names   after the places of production.

Three is generally medium to tall with an erect habit   densely foliaged   both thorny and thornless.

Fruits depressed   globose to oblate   orange yellow to bright orange   surface smooth   glossy   base even or obtuse   occasionally short necked   slightly ribbed   rind thin   soft   adherence very slight or none   segments 8  10   rag little to medium   pulp vesicles uniformly orange  coloured   coarse   very melting   flavour agreeable   juice abundant   orange  coloured. Sweetness and acidity well blended. Seeds 9  25 (usually 10  15).

Citrus Fruits

Citrus fruits rank third in area (2.44 lakh ha) and production (19.52 lakh tonnes) in India during the year 1984 85 (Report of the Working Group on Horticulture for Seventh Plan   1985 90). Citrus crops occupy about 9.62 per cent of the total area under various fruit crops and have about 8.21 per cent of the total production of fruits in India. Under citrus group many members are being grown but mandarins are the most important followed by sweet orange and limes. However   in this chapter   a brief account is also given on another three citrus fruits namely lemon   grapefruit and pummelo.

The sweet orange (tight skinned orange)   commonly known as mosambi   malta and sathgudi is an important citrus fruit of India. It is commercially grown in Maharashtra   Punjab   Rajasthan and Andhra Pradesh. Sweet orange is highly polyembryonic. The tree is medium to large in size. The shape of the grown up tree is roundish   sometimes slightly upright. Leaf apex is slightly blunt   petiole narrowly winged. Aroma of leaf is distinctly different from that of sour orange. The thorns are more of less marked. Fruit subglobose to oval in shape   orange in colour and 6  8 cm diameter. Rind (sking) is tight. The pulp vesicles are sweet orange is tinged   central core of the fruit is solid to semi hollow. The shape of the seed is very variable.

Climate

Sweet orange requires dry and semi arid conditions coupled with distinct summer and winter seasons with low annual precipitation. In general   low humidity and severe winter result in good colour development and external appearance in fruits whereas high humidity favours thin skin and plentiful juice. Strong winds   whether hot or cool   are injurious   and wind breaks are grown to protect the plantation. Under humid environment fruit turns insipid   and also there is more chances of attack of the live parasites such as lichens and Loranthes under high humidity and rainfall   sweet orange fruits have thin and smooth skin and more juice. However   taste is superior under dry conditions. High temperature and high evaporation during flowering and fruit set result in low yields possibly by increasing flower and fruit drop   and by reducing fruit set.

Soil

The sweet orange can be grown on wide range of soils   but medium to light loamy soils rich in organic matter   well drained having the pH range from 6 to 8 are suitable. Soil should be at least one metre deep. In shallow soils   the trees remain stunted and die early for want of proper moisture and nutrients. Salinity has negative association with yield.

Cultivars

The following are a few important cultivars of sweet orange.

Mosambi

The origin place of   mosambi   is said to Mozambique. Fruit is small or medium   subglobose or elongated in shape. The fruit has distinctive longitudinal furrows and bears a circular ring (areole) around and apical  end (styler  end). The rind is thin and tight and green or yellowish green in colour   it is difficult to peel. Pulp is less juicy and flavour is not marked. The fruit contains about 15 to 25 seeds.

  Mosambi   is an early variety. It is extensively cultivated in Maharashtra.

Blood Red Malta

It is introduced from Mediterranean region. Tree is comparatively dwarf. Leaves are small and oval and almost wingless petioles. Rind is thin and tight. The colour of the pulp is streaked blood red when fully ripe   juicy and sweet   acidity is 0.5 per cent   TSS 10 per cent   flavour is pleasant. The fruit contains 5  12 seeds or no seeds. The fruits are sometimes dried on the tree due to physiological disorder.

  Bloos Red Malta   is a mid season variety. It is mainly grown in Punjab   Haryana   Rajasthan and Uttar Pradesh.

Sathgudi

It is also known as Chini or Chinese orange. It has its origin place in Sathgur in Tamil Nadu (India). Fruit is medium   subglobose   areole absent. Rind is medium thick   smooth and finely pitted. The pulp is straw coloured juicy with good flavour. The fruit contains 12  20 seeds. This is a famous variety grown in Andhra Pradesh and Tamil Nadu. The fruits are available from October to February.

Pineapple

It has originated as a seeding in Citra   Florida. The fruit is medium to large sized   subglobose   orange in colour. Rind is thin   bright and glossy in appearance. Flesh is primrose yellow   juicy   sweet and having flavour like pineapple. The fruit contains about 12 25 seeds.

  Pineapple   is a leading variety of sweet orange in the United States. In India   it is cultivated in Punjab   Haryana and Uttar Pradesh. It is mid  season variety. It ripens in the month of December.

Washington Navel

It is originated near Bahia   Brazil and was introduced in 1870 into Washington (USA)   therefore   it obtained the name. The term   Navel   has been assigned to these oranges because the fruits having a rudimentary fruit embedded in the fruit apex. The fruit is globose to obovoid or ellipsoid   size large   colour orange yellow apex often slightly protruded or broadly nippled. Rind is thick   surface moderately pitted. The pulp is medium juicy with excellent flavour   seedless   segments 9 11.

  Washington Navel   oranges are early maturing and found promising at Kodur (Andhra Pradesh)   around Bangalore and Coorg (Karnataka). However   in Punjab it is not successful because the fruits tend to develop granulation. Trees are sensitive to heat and arid conditions   especially during bloom and fruit setting periods.

Jaffa

  Jaffa   a variety of sweet orange is from Palestine. It has wide adoptability. The fruit is medium to large sized   globose to ellipsoid apex and base rounded. Rind is medium thick   smooth and finely pitted. Skin golden yellow   changing to orange red at full maturity. Flesh colour is yellow segments are 9 12   juice medium and sweet with good flavour   central core is small. The fruit contain 8 16 seeds. It ripens in the month of November.

It is a mid  season variety. The tree grows upright   foliage is dense   cold resistant but it has alternate bearing habit.

Shamouti

This orange is the famous one for its seedless character. The origin place is Palestine. It is a mid  season variety and extensively grown in Palestine. It is believed to be a bud sport or bud mutant from the Bellady orange of Palestine. The fruit is ellipsoidal in shape   medium to large sized. Rind thick   firm   surface finely pitted   but relatively smooth. Pulp colour is light orange   juice medium sweet in taste with rich in flavour.

Valencia Late

The place of origin is probably in China. The fruit is medium to large sized   round to slightly oval in shape. The colour is golden yellow when mature. Rind is thin   smooth   tough   axis medium   solid or semisolid   sections 9  12. Pulp is orange in colour   juice content is more   sweet with excellent flavour. The fruit contains 5  6 seeds. It is a late maturing variety. It is cultivated in Punjab.

Hamlin

The place of origin is in Florida and named after the owner of the orange grove in which it was found in 1879   and developed as a chance seedling. Fruit medium orange red   apex rounded and slightly scarred   rind smooth   thin   bright   segments 11 12 uneven in size. Pulp juicy with excellent flavour. The fruit contains 1 5 seeds   sometimes fruits are seedless.

It is grown on large scale in Florida. In India   Hamlin oranges are grown in Punjab   Haryana   Uttar Pradesh. This is an early variety. This variety is reported to be more winter hardy than most sweet oranges.

Batavian

This variety has come from Batavia. Rind is tight   yellowish green with pale yellow patches on the green rind. The axis is hollow. This is mainly grown in Coastal districts of Andhra Pradesh.

Propagation

Sweet orange is commercially propagated by budding. Percentage of polyembryony varies from 40 to 95 per cent.

Raising of Seedlings for Rootstock

The seeds are extracted from fruits of the desired trees. They are treated with fungicides and then sown in well prepared primary nursery. Under good conditions   seeds germinate in 20  25 days. When seedlings attain 4  6 leaf stage are transplanted in the secondary nursery beds. While transplanting   seedlings in the secondary nursery   all type   sexual seedlings should be discarded leaving uniform upright and vigorous seedlings   which are true  to  type nuclear seedlings. The planting or seedlings in the second nursery is done at 20  30 cm distance both ways.

Budding

It sweet orange   budding techniques like patch   forkert or T  budding may be followed. The best time of budding is when the plant has good sap flow and the cambium tissue is highly active. Well swollen unsprouted buds   from about one year old non  angular branches are preferred. Budding should preferably be done at a height of about 20  25 cm from the ground level. The bud  graft or buddlings become ready for planting in 6  9 months after budding.

Planting

It is desirable to dig the pits well in advance to planting of sweet orange buddings or bud  grafts. The pits are dug 60 cm3 size in deep soil and 75 to 100 cm3 in shallow soil. The pits are filled up with 20  30 kg well rotten farmyard manure and good soil. The distance of planting may be 4 × 4 m or 5 × 5 m. Yield per hectare is increased with closer planting distance. A greater percentage of fruits is found in the upper parts of the trees planted at closer spacing whereas it is more inside in wider spaced trees.

Planting is done in the beginning of monsoon   where rainfall is light. Whereas in areas of heavy rainfall   it is done at the end of monsoon. Planting in spring is not advisable because spring planted plants have to pass through the ensuing summer. Further   plants will require irrigation at frequent intervals and protection from the hot and desiccating winds and high temperatures during the summer.

In North India   manuring is done in winter (December  January) with a second dose of ammonium sulphate applied in April  May after the fruit set. In Western and Southern parts of India   manuring is done before the onset of monsoon. Sometimes   the second application is also given in December or early January. Besides   application of micronutriens (Zinc   boron and iron) in the form of foliar feed or soil application improves the general health of the growing trees and results in improving the yield. Micronutrients help in controlling citrus decline. The choloritic condition of citrus leaves has been reported to be due to low availability of micro  nutrients which are especially more acute in calcareous soils.

Zn deficiency in sweet orange causes chlorosis in leaves. It is believed that Zn deficiency is caused by antagonistic effect of Fe on Zn availability. The critical level of      Zn in citrus leaves for clear distinction between healthy and chlorotic plants appeared to be 20 ppm. Generally   the healthy green leaves had lower concentrations of P and Fe and higher levels of N   Ca   Mg and Mn than chlorotic ones. The concentrations of K  S   and Cu are more or less in the same range in both cases. Soil samples supporting chlorotic plants had   in general   a low content of available Zn and a high level of available Fe.

Visual symptoms of Zn deficiency can be corrected with the soil application of 500 g ZnSO4 per plant in cv.   Blood Red Malta 

Alternate bearing (that has also been recorded in oranges) has been noted in   Washington Navel   oranges on sour orange rootstock. In the   Off   year leaf micronutrient contents (especially Zn and Mn) have been low but NPK contents have been higher. The opposite occurred in the   on   year. Foliar application of chelated Mn   Zn and Fe has been found to increase a level near that of control trees in the   On   year. It suggests that the balanced micronutrients application could help in reducing biennial bearing.

Irrigation

Just after planting and also after application of fertilizers   irrigation is given. Subsequent irrigations depend on climatic conditions and soil types. During the month of July to October when rains are expected   watering is done only where there is long spell of drought. During summers   irrigations at short interval of 7 days are needed. However   during winter the interval of irrigation extends to 12  15 days. Heavy soils require irrigation at wider intervals than light soils. Check basin system is usually followed. Care is taken that the irrigation water dose not touch the tree trunk directly and a dry area needs to be maintained near the tree trunk. This can be maintained by providing mound of earth around the tree trunk well below the bud union.

Flowering and fruiting periods are critical where irrigation should essentially be done. Non  availability of sufficient soil moisture during these stages will result in drop of flowers and newly set fruits. The third critical period is maturity period of fruits. During this period   water shortage results in shrinkage of the fruit and drying of pulp and very poor fruit juice.

Interculture and Intercropping

Shallow cultivation at 3  4 months interval keep down the weeds   provide soil aeration   help in conserving soil moisture etc. Deep cultivation at frequent interval will damage rootsystem   it depletes the soil organic matter   spoils the soil structure   creates plough sole and reduces water holding capacity of the soil   increases soil erosion   it is believed that it induces decline.

Sweet orange plantation can be intercropped with leguminous crops like berseem (Trigonela alexandrium)   lucerne and Phaseolus trilobus without any adverse effects on the yield and fruit quality. The other common leguminous crops are sunhemp (Crotalaria juncea). cowpea (Vigna unguculata)   dhaincha (Sesbania aculeata)   senji (Melilotus parviflora) vegetable crops like Tinda   Kadhu   Guar (Cyamopsis tetragonoloba).

Training and Pruning

Young plants should be given support if needed so that they do not bend. Sprouts arising below bud union and water sprouts should be removed as and when they are seen on the plant.

Sweet orange tree does not require pruning except unwanted (The branches touching the ground) diseased twigs are cut and removed out of the field. Sometimes   more twigs are required to be removed off from the trees grown at high plant density programme.

Bahar Treatment

Under western and southern parts of India   climate is mild therefore   sweet orange trees do not go in rest. Infact     resting   is essential for high production. Under mild climatic areas   growers like to have Mrigbahar crop   because this helps them to tide over the water scarcity in the months of April and May. It is done by withholding water 60 days in advance of the normal flowering season. And   about 30 days prior to commencement of flowering season roots are exposed by removing soil around the tree trunk. The depth of soil removal is about 10  15 cm or so. After about 6  10 days of exposure soil is back filled along with 20  25 kg of farmyard manure followed by light irrigation and which is followed by heavy irrigation for 4  5 days. In about 10  12 days there is profuse emergence of new flush of leaves and flowers. This treatment cannot be followed properly in the areas where rains are expected irregularly   especially in South India. Also   this treatment cannot be followed in North Indian climate where summer and winter seasons are quite distinct   in these areas the trees flower normally once in a year in the spring season (February  March). Root exposure always is not recommended.

Fruit Drop

In sweet orange   pre  harvest fruit drop is a common problem. The percentage fruit drop varies with different cultivars.   Mosambi   and   Malta Blood Red   are more prone to pre  harvest fruit drop than   Valencia Late.   The fruit drop may be due to mainly two reasons (i) physiological fruit drop   and (ii) pathological fruit drop.

Physiological fruit drop

In this type of fruit drop   the dropped fruits look sound and normal and have no apparent signs of any incidence of insect pest or disease. The following causes may be attributed   (i) Formation of abscission layer at the stem point. (ii) Imbalance of growth regulators   such as auxins   cytokinins   gibberellins etc. (iii) Excess or deficiency of certain essential nutrients. (iv) Unfavourable weather conditions. (v) Faulty cultural practices.

Mandarin

The mandarin group includes all types of loose jacket oranges commonly called by the Indian name Santra such as the Nagpuri Santra   Coorg santra   the Khasi orange and the Desi type. At present mandarins are commercially grown in India. The tree is small   spiny with a dense top. The leaves are long   lanceolate   petiole slightly margined   articulated   flower white   solitary   perfect. The size of fruit is yellow   reddish orange. The core is hollow. The rind is thin   rind and segments are easily separated. The number of segments is 10 14. The pulp quality is exceptionally fine. The seeds are small beaked   cotyledons green   highly polyembryonic   but wide range (10 100%) of it   is reported.

Uses

The fruits are used as table purposes.

The juice is excellent for drinking purpose.

Climate

Mandarins require subtropical and tropical climate. They grow well in submontane tracts with elevation from 600  1100m   and rainfall ranging from 75  250 cm.

Soil

Mandarins grow on a wide range of soils but for getting higher yields and having long productive life span of plantation   soils which are medium to light loam   deep   well  drained   free from excess salts and having adequate content of organic matter are most suitable. High content of organic matter in the soil is necessary for the effective combination of mycelia and mandarin root as they lack root hairs. The soil pH ranges from 5.5 to 8.0   is suitable for mandarins.

Varieties

Nagpur Santra

This is one of the finest mandarins grown in the world. The origin place is India and occupies the premier position. The tree is large   vigorous   moderately spreading   spineless with compact foliage. It is a prolific bearer. The fruits are medium in size   sub  globose in shape. The colour is not uniform but generally cadmium. Surface of the fruit is smooth and glossy. The base (stalk  end) is slightly drawn out and warty with glandular furrows. The rind is thin   separated very easily. The number of segments is 10  11. The amount of rag is little. Juice content is abundant   yellow in colour with excellent flavour   sweet in taste. The number of seeds per fruit is 6  7. The maturity period is generally January  February.

Khasi Orange (Mandarin)

It is commercially grown in Assam. The tree is generally medium to tall with an erect habit   dense foliage   both thorny and thornless. It is a prolific bearer. Fruits are depressed   globose to oblate in shape. Colour of mature fruit is orange yellow to bright orange. The surface of the fruit is smooth   glossy. The base (stalk  end) is even or obtuse   occasionally short necked   slightly ribbed. The rind is thin and is separated very easily. The number of segments 8  10   rag little to medium. The pulp vesicles uniformly orange  coloured   coarse   very melting   flavour aggreable   juice abundant   orange coloured. Sweetness and acidity well blended. The seeds very from 9 to 25 per fruit.

Coorg Orange

It is the most important commercial variety in South India. It is propagated by seed. The tree is large vigorous upright growth compact foliage   sparingly spinous. The fruits are oblate to globose in shape. The colour of fruit is bright orange yellow. The base necked or depressed with glandular ribs extending through the collar. The rind is thin and  soft   slight adherence   easily separated. The number of segments is 9  11   rag is little. Juice is abundant   deep chrome in colour. The number of seeds varies from 14  30 per fruit.

Desi Mandarin (Pathankot)

This variety of mandarin is mainly grown in the Punjab hills. The tree of this variety is large   with semi  upright growth habit having compact foliage. It is spinless. The fruit is ovoid to subglobose. Surface pitted   semi  glossy and finely wrinkled. The base of the fruit is shortly necked and furrowed   rind adherence is slight. The number of segments is 7  10. Juice abundant   deep chrome colour   the number of seeds per fruit varies from 3  7.

Kinnow Mandarin

Kinnow mandarin is a hybrid between King (Citrus nobilis Lour as parent) and Willowleaf (Citrus deliciosa Tenore as  parent) mandarins developed by Dr. H.B. Frost at Citrus Experiment Station   California (USA) in 1915. It was first introduced in the form of virus free budwood and raised on Jatti Khatti (Citrus jambheri) rootstock in 1959 at the PAU Regional Research Station   Abohar from the University of California. It is cultivated in the Punjab   Haryana   lower hills and velly areas of Himachal Pradesh   Uttar Pradesh   Karnataka   (Coorg   Hassan and Chikmangalore district)   Kerala (Wynaad and Palghat district)   Tamil Nadu (Ootacamund and Madurai districts). In north India   the  cultivation of mandarins is limited due to the acidity and puffiness of the fruit. Kinnow has been proved promising in place of mandarins because kinnow has wide adaptability to variable agro  climatic conditions and also comparatively more resistant to insect  pests and diseases. Incidence of fruit drop due to hail storms or other reasons is also comparatively less. Kinnow is usually less prone to bird damage   as almost two  thirds of the fruits are known to bear in the interior of the tree.

Kinnow mandarin grows vigorously. Trees possess dense foliage and lush green in appearance. Kinnow fruit is medium in size and is globose to oblate in shape. The apex is flattened. The number of segments is 9  10. The axis is semi  hallow. The colour of fruit is attractive shining deep orange at ripening. The peel is thin   glossy and also adherent   but can be peeled off easily by hand. Juice is abundant (50%) having good contents of TSS (15%) and sugar (11%) with good flavour. Seeds vary from 14  19 in number and are polyembryony.

Climate

Kinnow can be grown under variable agro  climatic conditions. It can tolerate even frost if it occurs for only a couple of days. The submountainal climate produces fruits of high quality.

Soil

Kinnow thrives well on deep fertile   sandy loam soils having pH ranged of 6.5 to 7.5. It is not advisable to establish kinnow orchard on soils which are saline   alkaline or having a lime concretion layer in the lower horizons.

Propagation

Kinnow is highly polyembryonic (75%) and thus seedlings also come true to type after removal of sexual seedlings at nursery stages. But to raise plant further hardy   it becomes necessary to propagate them on hardy rootstock like karna khatta (Citrus karna Raf.) and Jambheri (Citrus jambheri). The method of budding   time etc. are similar to mandarins.

Planting

The pits are due at the distance of 5.5×5.5 m with dimensions of 60  75 cm   and they are filled with a soil mixture consisting of one part FTM or compost and three parts top soil. The pits are left as such so that soil settles well in the pits. Planting is done in the centre of the pit. While planting   care is taken to avoid burying of bud  union portion in the soil. The best time of planting is in the months of August  September.

Manures and Fertilizers

A bearing kinnow tree may need application of 80  100 kg of FYM   400  600 g of nitrogen   200  300 g of phosphorus and 400 go of potassium for good growth and production. The total amount of phosphorus and potassium and half amount of nitrogen are applied during February  March and the remaining half of nitrogen during September  October. Application of urea at one per cent   zinc and manganese at 0.5 per cent as zinc sulphate and manganese sulphate    respectively   during the main flushes is beneficial to overcome the zinc and manganese deficiencies which are very common.

Irrigation

Kinnow plantation requires very light and frequent irrigation. During summer   irrigation is given at an interval of 8 to 10 days. During winter   it is done at 20  25 days intervals. Generally   irrigation is not needed during rains except where there is a long break.

Interculture and Intercropping

Young plants of kinnow require hoeing twice or thrice in year to keep down the weeds and to provide good conditions for growth. Bearing orchards are ploughed and harrowed after monsoon is over for proper cleaning.

Kinnow trees attain yield stablization by the age of 12  15 years. By 8  10th year the trees start yielding good profit. It is better to discontinue intercropping by 7th or 8th year. Suitable intercrops are : Moong   urd   pea   cowpea   cabbage   okra and potato.

Flowering and Fruiting

Kinnow plants start bearing flowers and fruits 4  5 years after planting. It has precocious bearing and very high fruit yield during early years of its life. Because of so heavily bearing   the tree get hausted leading to collapse or gradual decline. Among other factors   the malnutrition seems to be the major cause for declining of bearing trees. Not only this   kinnow trees show tendency of irregular bearing. That is   heavy crop year is followed by poor crop year with small fruits of poor quality. The alternate bearing tendency of kinnow plantation can be improved up to certain extent with the help of growth regulators. Among them   NAA at higher concentration has been found to act good fruit thinner and there by reducing the crop load in heavy crop year. NAA is also easily available and convenient in use. Application of NAA 350 ppm 30 days after full bloom induces reasonably amount of fruit thinning and help in regulation of the crop in the subsequent year. Another effective method of hand thinning but it cannot be followed on large scale except with kinnow trees growing in backyard.

Harvesting

Being non  climacteric   kinnow fruits fail to ripen after harvesting and do not improve in taste after harvest   unlike many other climacteric fruits like mango   peach and banana. Therefore   kinnow fruits should be harvested only when they are fully ripe   attractive orange coloured and acceptable sugar  acid blend. The best time of picking Kinnow in north India is from end of January till the first fortnight of February. In earlier picked fruits   acidity is higher and fruit is sour in taste. The fruit should be harvested with a clipper   retaining a short twig button  end along with the fruit. Pulling the fruit from the branch ruptures the skin near the stem  end   leading to fungal infection and subsequent rotting of the fruit. The fruits should not be harvested during or immediately after rain or when they are covered with dew   because by absorption of water the peel becomes soft and turgid and is bruised during handling.

Yield

Well grown up kinnow tree of about 10  12 years age bears about  2000 to 5000 fruits. However   yield potential of tree depends on climatic conditions   soil types   freeness of pests and disease and management practices.

Sour Lime

Sour lime (Kagzi lime   Acid lime   Mexican lime) in Hindi is known as   Neebu  . It is a profusely branched thorny shrub or small tree. The leaves are small with narrowly winged petioles. The flowers are small   pure white and are borne in clusters. The fruits are more or less round or oval   smooth having thin rind (papery) attached lightly. The immature fruits are dark green in colour   which changes to light yellow when ripe. The colour of the pulp is light greenish yellow   taste is acid   aromatic   cells fine and shiny. The number of segments is 9  11. The number of seeds per fruit is 9  10.

Sour lime is found in most parts of the tropics. In India   it is cultivated in Tamil Nadu   Maharashtra   West Bengal   Punjab   Madhya Pradesh   Andhra Pradesh   Delhi   Uttar Pradesh   Karnataka   Gujarat. It is cultivated in the plains and up to 1200 m elevation. The small fruited lime is the variety grown all over India. A large number of types differing in size   shape and colour of the fruits are cultivated. Some thornless types are known but they are not grown commercially.   Bearss   or   Sersian   is very important type in Florida: produces fruits larger than the conventional lime   totally seedless   smaller and less thorny tree   easier to harvest.

Climate

Sour lime requires tropical climate. It is tender to frost. Strong winds are harmful. In the more humid areas of Assam and West Bengal where the rainfall is above 125 cm   the lime becomes highly susceptive to citrus canker   which makes the trees unproductive and short lived. Sour lime may not be cultivated in the area where the temperatures occasionally fall below the freezing point. Sour lime is successfully cultivated in west and south India where winters are free from frost and the annual rainfall does not exceed an average of 75 cm. Sour lime can successfully be grown from sea level to 1000 m or so elevation.

Soil

For the plantation of sour lime   soil should be atleast 1.5 m deep. It should be well drained. Heavy soils should be avoided for planting. A high water table of a permanent or fluctuating nature is unsuited and low  lying localities which are subjected to water stagnation should always be avoided.

Types/Varieties of Lime

Kagzi Lime

It is the best variety grown all over the country. It has two types of fruit   round and oval.

Chakradhar Lime

This variety of lime was derived from cv   Kagzi. It has round fruit with thin papery rind   and a 60 66 per cent juice content. It is a thornless and seedless selection. It has a greater yield and vitamin C (ascorbic acid) 118.2 140.8 mg/100g and acid content (8.3 9.1%) than   Kagzi. Trees of   Chakradhar   begin bearing in their 4th year and are compact and semi spreading.

Rangpur Lime (Citrus limonia Osbeck)

Rangpur lime is indigenous to India. It is fairly tolerant to frost. It is commonly grown for rootstock purposes because it is more hardy than true lime. However   it is susceptible to citrus scab. The fruits are used for making limeade. In fact   it is not true lime. The fruit has loose rind and segments are easily separated. The pulp is light orange yellow in colour. The seeds are small   cotyledons green   polyembryonic.

Taheti (Persian) Lime (C. latifolia Tanaka)

It is a native of south pacific. It is a triploid and produces no viable pollen. It might be a hybrid between lime and lemon or even a distinct species.

Propagation

Sour lime is mainly propagated by seed. Propagation by seeds is followed due to polyembryonic nature of it. In sour lime about 78 per cent seeds possess polyembroys. Each polyembryonic seed produces three to four seedlings. Among them   one is sexual origin and remaining are nucellar. Nucellar or apogamic seelings breed true to type. Besides   vegetative methods like budding   layering and stem cuttings are also adopted   but only on small scale.

In Punjab   sour lime is usually propagated by ground layering. The healthy   flexible branches which are close to ground are selected in the month of February  March. The selected shoot is notched or a ring of bark is removed   in order to encourage rooting   before burying the shoot in the soil. The portion from which roots are to be emerged   should be properly buried in the soil making top portion free for growth. A piece of stone or brick is kept on the portion subjected to layering so that it is kept in position till rooting is over. The soil is always kept moist for encouraging rooting.

Root formation is over by 8  10 weeks. Thereafter   the layer is cut from the mother tree and lifted for planting in pots or in the main site.

Raising of Seedlings

Freshly extracted seeds are sown on well prepared nursery bed at the distance of 20 × 10 cm and 1.5 to 2 cm deep. Germination completes within 3 weeks. The sexual seedlings   which are usually stunted and poor in growth compared to apogamic or nuclear seedlings   are uprooted carefully. Removal of sexual seedlings is essential because they do not breed true to type. The apogamic seedlings are identical to the parent in growth and production. Seedlings are ready for transplanting 6 to 9 months after sowing. However   usually one year old seedlings are preferred for transplanting.

Planting

The pits are dig during summer with a dimension of 60  75 cm3. They are filled with a mixture of top soil and well decomposed compost or farmyard manure at the ratio of 50 : 50. The filled pits are left till first shower of monsoon. Planting is done in the centre of the pit with a single healthy seedling or graft. The root zone of transplant is set properly and pressed around it. Planting is followed by irrigation in the absence of rains.

Sour lime is planted at a distance of 5 × 5 or 6 × 6m. Distance can further be reduced to 6 × 5   6 × 4 m if soil is poor. The lime tree declines after certain period of cropping   but it is early   if they are planted closer. But decline can be prevented by removing alternate row of plants or alternate plant from the row   that will provide sufficient growing spaced and will avoid competition for essential requirement like solar radiation   water and nutrients. Closer plantation has also been reported to have more incidence of pests and diseases which may lead to decline and reduced production.

The best time of sour lime planting is the onset of monsoon. The survival and establishment of lime plants remain very high during monsoon season. However   planting can also be done during September October of February March   when assured irrigation facilities are available.

Manure and Fertilizers

Generally   about 50 kg of FYM   500 g N   400 g P2O5 and 900 g K2O per plant from fifth year and onwards   every year it is applied first in December  January before spring flowering   and the second application is done in June  July. These timings of application can be adjusted according to climatic conditions of the region in which it is grown.

However   the following doses of fertilizers (g/tree) and FYM (kg/tree) are applied in different states.

Irrigation

As stated earlier   the very first irrigation is done just after planting. Subsequent irrigations are needed during rainy season if rains are regular. During winter   lime plants are irrigated 15  20 days intervals whereas during summers at 8  10 days intervals. Sufficient soil moisture is maintained during fruit setting and fruit development.

Interculture and Intercropping

During rainy season   weeds become a problem   hoeing once or twice will keep down all the weeds. Proper cleaning is done during post monsoon season during (September October). Only shallow cultivation should be done. Much of clean cultivation practices will not be beneficial.

Sour lime is a evergreen in nature   after harvesting it should be given some rest during the month of October to November   in the South and Western India   and in the month of December and January in the North India   developmental stages which results in high percentage of fruit retention (i.e. low percentage of fruit drop and ultimately high fruit yields).

Sour lime tree develop full canopy in 4 to 6 year. Intercrops can easily be taken during early stages of crop growth depending upon population density. Usually vegetable crop   particularly legume vegetables are grown with advantages.

Training and Pruning

The young plants may be provided with support with bamboo split sticks if needed. Later when new sprouts form near to ground level are removed as and when they are seen. Bearing trees may be pruned for unwanted branches like criss  cross branches   diseased and dead and branches which are profusely growing on the ground   and the water sprouts. Pruning operation provides good framework to the tree   which should be attended to yearly.

Flowering and Fruiting

Sour lime starts bearing flowers and fruits from the fourth year onwards after planting. Under natural conditions   the trees flower all the year round each flush bringing forth new blossom. The fruits mature in six months after flowering. In Gujarat   about 60 per cent of the total crop is harvested during July to September   30 per cent from October to January and 10 per cent from February to May. In north India   the main harvesting season is in the months of August  September.

Higher fruit setting   minimum fruit drop and higher fruit yield of sour lime are obtained with the spraying os ZnSO4 at 0.6 per cent + 2   4  D at 20 ppm in early January for the spring flush and in early May for the summer flush followed by GA3 at 50 ppm + ZnSO4 at 0.6 per cent.

Sweet Lime

Sweet lime (Mitha neebco) has non acid juice unlike sour or acid limes. It bears very profusely. Its fruits are seen in the markets much before the arrival of oranges. The sweet lime is a large and spreading tree with medium size leaves characteristically   somewhat rolled and cupped   pale green in colour with prominent oil glands and naked to margined petioles. The flowers are large and pure white. The fruit is globose or ovoid   generally with low   flat papilla. The rind is tight   smooth   thin and light green but lemon yellow on full maturity. The sections in the fruit are closely set. The colour of flesh is yellowish white. The content of juice is abundant   taste is sweet insipid   devoid of acidity. The number of seeds per fruit varies from none to five. The fruit shape   foliage characters   light coloured inner seed coat an chalazal spot are very distinctive characters   light coloured inner seed coat an chalazal spot are very distinctive characters. Polyembryonic characters of sweet lime suggest that it is probably hybrid that is nearly sterile. The possibility of hybrid between Mexican lime and sweet citron was reported   and therefore   sweet lime was placed provisionally under limes.

In India   sweet lime is commercially grown in Punjab   Tamil Nadu and Assam. It is also grown on small scale in other parts of India. Infact   its cultivation is limited to home gardens.

Climate

The sweet lime can be grown under a wide range of climatic conditions. It is more hardy in nature than Kagzi lime. It is tender to frost but can withstand frost conditions better than Kagzi lime. It can also grow under dry conditions. It also grows successfully at higher altitude in Assam.

Soil

The sweet lime can be grown on a variety of soils. However   ideal soils are well drained deep loams.

Varieties

Mitha Chikna

The plant is medium tall   spreading   densery orange and thorny. It is a prolific bearer. The fruit is almost spherical or globose   light yellow   surface very smooth and glossy. Rind is very thin   leathery   adherence medium to strong. The number of segments is 10 to 11. The pulp vesicles uniformly white. Juice is abundant   taste sweet or insipid sweet   flavour aggreable. The rag is medium. The number of seeds per fruit is one to five. Seeds are white in colour and chalazal spot are light yellow.

The other variety is large fruited (the fruit look like grape fruit). The colour of fruit is lemon yellow   apex slightly depressed   base slightly necked   the ring is rough and thick and oil glands are prominent. The flesh colour is yellowish white. Juice is abundant   nice taste   flavour aggreable and rather better than of the mitha chikna variety.

Propagation

Sweet lime is commercially propagated by hardwood stem cuttings. However   it can also be propagated by budding   air  layering   and occasionally by nucellar seedlings. Sweet lime is highly polyembryony   the average number of embryos per seed has been reported as 5.8.

The hardwood cuttings are prepared from selected shoots of  consistently high yielding trees. The cuttings are best rooted during the monsoon season under open conditions. The root formation in cuttings can be enhanced by the application of IBA at 3000 ppm by quick by method. Under favourable conditions rooting completes in 4 to 6 weeks. However   the plants raised from stem cuttings are generally shallow rooted and are surface feeders   which is a demerit.

Air layering is also done successfully in the commencement of rain. In about four months time   the layer is ready for separation.

Propagation by shield budding is successful provided that the operation is performed in March April   and only the current seasons (immature) bud wood is used. The suitable rootstock is jatti khatti (rough lemon) in the Punjab   Soh myndong (rough lemon) in Assam   Karna Khatta in Uttar Pradesh and Jambheri in other parts of the country.

Planting

The pits are dug at the distance of 6 × 6 m with the usual dimension of 100 cm3 to 75 cm3 depending upon the soil and climatic conditions. They are filled with top soil or silt mixed with well rotten farmyard manure. Thereafter   they are watered copiously and left for a few days to allow the contents of the pits to settle down.

Usually   sweet lime is planted in the onset of monsoon in the areas where monsoon are light. However   it is planted in September that is post monsoon season or during the period when rains are light and occasional.

Lemon

The lemon (Bara nibu) has its ancestral form   the galgal which is also in cultivation. The word lemon is derived from the Arabic word Linum means for lemon. In India   it is cultivated in Uttar Pradesh   Maharashtra   Tamil Nadu   Karnataka   Andhra Pradesh   Assam and the Punjab. In the north   the lemon fruits are available from December to February when the Kagzi lime is either not available or is rather scare. The lemon trees are relatively free from diseases like die  back   wither  tip and canker to which the sour lime is very susceptible.

Lemon is a straggling bush or a small tree with thorny branches. The leaves are slightly ribbed and have a distinct joint at the beginning of the blade. The petiole is wingless or very slightly winged. Flowers are purple in colour. Fruits are obovate to elliptical or oblong in shape. The areolar area protruding as a pointed nipple. The rind is thick and lemon yellow in colour. The surface of the rind is slightly rugose. The pulp is acidic in taste and pale yellow in colour.

Climate

Lemon requires sub tropical climate. It flourishes under semiarid conditions. It can tolerate frost better than Kagzi lime. It is grown up to 1200 m elevation   it yields prolific crops both under irrigated and rainfed conditions. Lemons are more hardy than Kagzi lime.

Soil

Lemon is adaptable to a variety to soils. However   it requires well drained shallow soils to a depth of not less than one metre. The area on which lemon is planted   should be protected from strong winds by means of suitable windbreaks.

Varieties

Eureka

This variety was introduced from America and Europe   and best suited in the Punjab and Western parts of Uttar Pradesh. Tree medium to large   spreading   open   sparingly spinous. The leaves are large size   dark green   margin markedly crenate   apex blunt   pointed or rounded.

The fruit is medium in size and obovate to elliptical or oblong in shape. The rind is medium thin   colour lemon yellow   surface slightly rugose   pitted   usually with inconspicuous longitudinal ridges. The apex of the fruit is abruptly rounded and areolar area protruded into a slight or prominent nipple. The fruit axis is small and semi  hollow to solid. The number of segments is 9 to 14. The pulp tender   fine grained   pale greenish   vesicles slender and conical to spindle shaped. The content of juice is abundant   very acid   and flavour is excellent. The fruit contains at few seeds   none to 6 or more per fruit. The juice has TSS of 8 per cent and acidity 5.47 per cent.

Lisbon Lemon

The tree of this variety is large   spreading open   rather thorny. This is another introduced variety. The fruit is medium in size. The shape is oblong to ellipsoid. The rind is medium thin   colour lemon yellow to lemon chrone   surface smooth or rugose   pitted   inconspicuous ribbed. The base of fruit is rounded to slightly protruding. The apex of the fruit is prominently nippled. The axis of the fruit is small and solid to semi hollow. The number of segments is 9 to 11   sometimes seven. The pulp is fine grained   cream coloured   vesicles conical to spindle  shaped   slender. The content of juice is abundant   very acidic   excellent quality. The fruit contains none to ten or more seeds. The juice having about 8 per cent TSS and 5.92 per cent acidity.

Villafranca

It was introduced into Florida from Europe about 1875 and is grown on large scale in Florida. The tree is large   vigorous with dense foliage. Twigs are thorny. The leaves dark green   large   broadly lanceolate. Fruit ovaloblong   medium to large  sized. The colour of fruit at full maturity is lemon yellow. The apex of fruit is pointed   blunt   base rounded. The rind is smooth and thin. The number of segments is 10  12. The seeds are about 25  30 per fruit.

Lucknow Seedless

The tree of this variety is medium in height. The branches are dropping and thorny   foliage dense and light green. Leaf petiole is marginally winged. Fruit is oblong in shape   lemon yellow in colour. The rind is smooth and thin. The fruit apex is nippled and the base rounded. The axis is hollow. The number of segments is 9  13. Juice is abundant. Seeds are usually absent. The main season for availability of fruits is during November to January.

Nepali Oblong

Tree small to medium sized   crown irregular   foliage dense. The leaves are broad and elliptical. Fruit is oblong to obovate in shape. The colour of the fruit is lemon yellow   the apex is nippled and the base rounded. The rind is medium thick. The axis is hollow. The number of segments is 11  13. The seeds are very few or absent. The main season for availability of fruits is December  January.

Baramasi

Tree medium and vigorous   spreading   shoots numerous   foliage light green   dense   leaves medium in size   broadly lanceolate   fruit colour lemon yellow   surface smooth   shape oblong   size small   base short but inconspicuous   apex gradually rounded   rind thin   segments 8  10   pulp fine grained   pale greenish yellow   juice abundant   clear   very acidic   quality excellent   seeds 4  14 per fruit.

Kagzi Kalam

Tree medium   hardy and vigorous   spreading   foliage light green   dense   elliptical to oblong   margin crenate   apex obtuse  acute   petiole winged. Fruit medium sized   oblong yellow   apex slightly nippled   rounded base rind thin   axis hollow   segment 9  12. Pulp light yellow juicy flavour good and sour. The number of seeds per fruit varies from 8  19.

Hill Lemon. (Galgal) C. pseudolemon Tanaka

Galgal is indigenous to northern India. Commonly grown in sub  Himalayan regions. The tree tall   hardy   vigorous and uprightly growing. Foliage is dense and twigs have thorn. The leaves are broadly elliptical with long marginal winged petiole. The fruit is ovate  oblong   apex slightly nippled   base rounded to slightly nippled. The rind is medium thick. The axis is hollow. The number of segments is 8  10. The number of seeds per fruit is about 25  60. The fruit ripens from October to December. Propagation by stem cuttings is successful.

Hill lemons are mainly used for making pickles   squashes and candy.

Meyer Lemon

It was introduced into the United States from China in 1908. The tree is semi  dwarf   thornless   resistant to cold. The leaves are small. The fruit is obovate to elliptical or oblong. The colour of fruit is light orange. The rind is thin surface is smooth. The apex round and base is also round sometimes slightly necked and radially furrowed and lobed. The number of segments is 10. The number of seeds is 8  12. It gives fruits throughout the year with main season from November to January.

Pat Lemon

It is an indigenous lemon variety of Assam where it is called Assam lemon. It is also found growing south India and South Maharashtra. Where it is known as Pal Nimboo. It is a chance selection from a variety of lemon known as China  Kaghi in Assam. It is grown under the name of Seville lemon in Andhra Pradesh. The variety is tolerant to scab   canker and gummosis.

The tree of Pat lemon is small   straggling   open   rather spinous. The fruit is ovoid  oblong   medium. The colour is citron yellow   surface smooth to finely rugose   base rounded to short  necked   apex obtusely nippled   axis medium and semi  hollow to hollow. The number of segments is 9 to 12. Pulp is greenish white   vesicles slender   conical to spindle  shaped. The seeds none to several in a fruit. The total solids are six per cent and acidity 5.6 per cent.

Italian Lemon

This has been found to grow well in southern states. It can be grown under high rainfall areas. The fruits are large oval with a prominent nipple. This variety is almost seedless.

Rajamundary Lemon

This variety has been found to grow in certain parts of Andhra Pradesh. Yield potential is high.

European Lemon

This variety is found growing in the north. It is very resistant to frost injury and the citrus canker disease. The fruit is almost of the size of galgal. This is a high yielding type.

Ponderosa Lemon or Japanese Lemon

It is truely a baramasia lemon. The tree continues to flower throughout the year and   as such   fruits of all sizes and stages of maturity can be seen on the tree any time. The tree does not take much growth. It is suitable to grow in home gardens but not suitable for commercial growing.

Malta Lemon

The tree is dwarf bushy and compact. The size of fruit is small to medium. Juice is abundant. The seeds are numerous. Malta lemon is found growing in the southern states. Trees of this variety start bearing in the second year of their planting in the sandy tracts of the west coast.

Propagation

Lemon is mainly propagated by seeds. The seeds are extracted from healthy fruits. Freshly extracted seeds are mixed with ash and dried in the shade. It is advisable to sow the seeds soon after extraction within three days   otherwise viability of the seeds is reduced. Propagation of lemon by seed is not preferred nor it is advisable to follow due to variabilities.

Lemon may be propagated by budding   layering marcotting and stem cuttings. Among them   budding is preferred   as resultant trees raised from budgraft are precocious   produce more uniform crop   and root and trunk diseases can be avoided by using suitable rootstock. Commonly adaptable rootstock are jati Khatti (Citrus jambheri) and Karna Khatta (Citrus Karna).

Planting

For planting of lemon   the pits are dug well in advance to planting operation. They are dug at the size of 60  75 cm3 or so depending upon cultivar   type of soil and topography of the land. The pits are filled with a mixture of top soil and 10  15 kg of well rotten farmyard manure or compost.

The pits are dug at the distance of 6 × 6 m. Italian limes are planted at a distance of 8 × 8 m because they put on more growth and develop into large canopy.

The time of planting lemons is in the onset of monsoon. However   lemon can also be transplanted in the month of September  October or February  March   if assured irrigation facilities are available. Planting is followed by staking and or light irrigation for better survival and establishment of lemon seedlings/grafts and putting on further growth.

Irrigation

Just after transplanting light irrigation is given. Subsequent irrigations are given as per need of the crop. During the hot summer months   irrigation should be given at 8  10 days interval whereas 10  15 days or so during winter. Adequate soil moisture should be maintained during flowering and fruiting stages.

Manure and Fertilizers

Lemon responds well to manure and fertilizer application. The doses of fertilizers very with the climatic condition   soil type and age of the tree. The below are the doses of manure (kg/tree) and fertilizers (g/tree) are being applied in states like Andhra Pradesh   Arunachal Pradesh   Assam   Karnataka and Rajasthan. Generally fertilizers are applied thrice in a year i.e.   in December  January   June  July and September  October. Farmyard manure is applied in June  July or September  October.

Grapefruit

The grapefruit has its well known ancestor the shaddock or pummelo (C. grandis). It has separated from pummelo in 1830 by James Macfadyen and assigned as species status (C. paradisii). The grapefruit is cultivated in all the sub  tropical regions of the world. The name of grapefruit has been given to this type because its fruits are borne in clusters much like grapes. It is cultivated in the USA   Palestine   South Africa   Brazil   West Indies   Australia and New Zealand. In India   it is cultivated in the Punjab   Western parts of Uttar Pradesh   around Pune in Maharastra and Deccan Plateau. Grapefruit can be safely cultivated in Rajasthan   parts of Madhya Pradesh and South Saurashtra where irrigation is available.

The grapefruit is a large   round topped tree with a dense foliage   twigs are angular when young   leaves are large than those of the sweet orange   but smaller than those of pummelo. The petiole is broadly winged   but comparatively less than those of the pummelo. The flowers are large in size   they are borne singly or in small clusters in the axis of leaves. The size of fruit is larger than that of sweet orange   but smaller than the pummelo. The shape of fruit is globose or pear  shaped having white or pink flesh. Juice content is abundant and it is mildly bitter. The seeds of grapefruit are smooth as compared to the ridged ones in pummelo   white and polyembryonic.

The grapefruit contains considerable quantities of Vitamin C and fair quantities of Vitamins A and B. It also contains minerals such as calcium   iron and phosphorus. The grapefruit juice particularly aids digestion and increases appetite. It produces an alkaline reaction in the stomach. The cellulose in the pulp of the grapefruit and the acid in the juice are laxative in effect   and thus they aid in keeping the digestive tract always clean and healthy. The grapefruit juice is low in calories. It has been found to be a good solvent of surplus body fat and therefore   useful in combating obesity. The bitter glucoside     Naringin   prevents against malaria. The grapefruit juice is beneficial in preventing enterites   dysentery and diarrhoea. Juice has also been found helpful in preventing and curing diseases such as acidosis   anaemia   chlorosis   scurvy   beriberi and rickets.

Climate

Grapefruit thrives in the dry and arid plains where the summer temperatures rise to 115ºF   the winter temperatures occasionally go below freezing point   and the rainfall ranges from 15 to 150 cm during the south west monsoon. Young plants may be damaged by frost and   therefore   have to be produced by a thatch of grass. The grapefruit can be grown upto 500 to 1000m or so altitudes a higher rainfall and a higher atmospheric humidity are detrimental to its growth   and encourage the spread of citrus canker   which kills young growth and disfigures the fruits.

Soil

For successful cultivation of grapefruit   well drained   deep and free working alluvial loam soils are the best. However   this can be grown on medium black soils of Deccan plateau provided that they are at least 1 to 1.5 m deep. Shallow soils are unsuitable because   due to the limited soil space   the roots can not expand and grow properly. Similarly calcarious soils containing large quantities of lime are quite unsuitable.

Varieties

Marsh Feedless

It was introduced into India from USA. It is one of the best commercial varieties. It is high yielding. It is nearly seedless. The fruit is medium to large size. The shape of fruit is ovoid globose to oblate. The colour when rise is light yellow. The surface of rind is smooth and glossy. Thickness of rind   medium   leathery and moderate adherence. The pulp is colonial buff   fine and tender. Number of segments vary from 11 to 14   axis mainly solid but sometimes semi  hollow. Juice is abundant with excellent flavour. Only a few seeds are found which are large sized   white when cut. The juice having TSS about 9 per cent and acidity 1.5 per cent.

The fruits of this variety can be held longer on the trees without any deterioration due to its seedless character. The variety Marsh Seedless belongs to Pallid pulp group of grapefruit.

Duncan

Duncan variety of grapefruit originated as a chance seedling in Florida.   Duncan   variety of the grapefruit is the next best to   Marsh Seedless.   It bears very heavily under Indian conditions. It is medium to late variety. The fruits are large   ovoid globose to oblate and sometimes oblique. The colour of the rind is light yellow (Chrome lemon)   the surface is smooth and glossy and the thickness of rind is medium   leathery with moderate adherence. The pulp is colonial yellow   fine and tender. The segments vary from 11 to 14. The axis is solid to semi  hollow. The juice abundant   flavour and aroma are very pleasing   acidity and bitterness are moderate. The juice having 9.5 TSS and about 1.1 per cent acidity. The fruit contains numerous seeds   usually varies from 30 to 60 or so   they are medium to large  sized   white when cut. The variety   Duncan    belongs to Pallid pulp group

Foster

This variety originated as a bud sport on a Walters grapefruit tree and discovered in 1906 1907 by R.B. Foster and was named after him.

Among pink or red pulp group   Foster strain is the best one. It bears prolifically under Indian conditions. The fruits are medium to large   ovoid globose to sub  globose. The colour of the rind is narcissus   flushed with pink (Salmon)   surface coarsely pitted and glossy. The rind has medium thickness   leathery with moderate adherence. Mesocarp is ivory yellow wity pinkish shade. The pulp is pinkish (Salmon)   fine and tender   segments are 12 to 16. The axis is semi  hallow. The juice is fairly abundant   flavour and aroma are pleasant and having medium acidity and bitterness. TSS is 10 per cent and acidity 1.15 per cent. The fruit contains numerous seeds (30 to 60 or so)   they are medium to large sized   white when cut.

Saharanpur Special

This variety was developed at Saharanpur Botanical Garden. This is successfully cultivated in Saharanpur and nearby area in Uttar Pradesh   and in the Punjab. The fruit shape is round to oblate   empire yellow   surface smooth   base round or slightly depressed   apex slightly depressed. The rind is medium thick. The axis is semi solid or slightly hollow. The number of segments is 12 14. The pulp is light yellow   and soft   vesicles loosely packed   juicy   flavour fair and sweetish sour. This variety has numerous seeds in its fruit. Fruit ripens from November to February. The variety   Saharanpur Special   resembles the   Marsh Seedles   in many characters except number of seeds per fruit.

Ruby

It is a budsport from the Thompson grapefruit and found in Texas in 1929. It belongs to pink or red pulp group. It resembles in almost all characters to the cv. Thompson or the Marsh   except crimson flush on its smooth rind   and has finely textured pulp of ruby hue. The deep red colour is uniformly distributed throughout the pulp. Ruby grapefruit is being planted extensively in Texas.

Thompson (Pink Marsh)

This variety comes under pink fleshed group. It is a bud sport from a typical Marsh tree in Florida. It is very successfully growing in south India. It is an early type and bears well under south Indian climatic and edaphic conditions.

Triumph

This variety is high yielding and prolific bearer   but not successfully grown. The main drawback of this variety is to have a tendency for drying juice sacs.

Propagation

The grapefruit is successfully propagated by budding on commercial scale. The Jatti Khatti rootstock (C. jambhiri) has been found to be a very compatible rootstock in the South India   Karna khatta (C. karna) has given outstanding performance in the north India   particularly in Uttar Pradesh. In Assam   the grapefruit does well on pummelo. However   in the Punjab   from recent studies it has been clear that the grapefruit cv.   Marsh Seedless   budded on Carrizo and Troyer (C. trifoliata × C. sinesis Osbeck) produced maximum tree volume girth and the maximum fruit yield and quality compared to the trees budded in Jatti Khatti (C. Jambheri) and Karna Khatta (C. karna Raf). The grapefruit is polyembryony and varies from 60 to 95 per cent (6   13   14). Due to its polyembryonic nature   seedling trees have been frequently found to be quite satisfactory.

The operating like planting   irrigation   manuring and inter culture for the grapefruit are just the same as for oranges and lemons.

Planting

As far as possible   the grapefruit orchard should be well protected from hot winds during summer   especially in northern India. At least one or two year advance to planting of grapefruit   a wind break of some quick growing tree like Shisham should be planted on the south  western side.

First of all   the land is ploughed   harrowed and levelled. The plot is demarketed and spots are marked at the distance of 6 × 6 to 8 × 8m. This pits are dug 60  75 cm3 and filled  with topsoil mixed with about 10  15 kg of well decomposed farmyard manure 1 kg of bone meal and 2 kg of woodash   if available.

The best time of planting of grapefruit is the onset of monsoon in southern India   whereas in the north planting is done in the months of January February. The plants are planted in the centre of the pits. While planting   the bud joint should be kept well above the ground level.

Irrigation

Just after planting   light watering is done for better survival and establishment. Irrigation is done by adopting basin method   basins are made to 60 cm radius round the trunk. The size of the basin should be increased from time to time to suit the ever increasing size of the plant. During dry season   young plants need watering throughout the year. However   irrigation applied from the flowering stage to fruit maturity has been found to be more effective than frequent irrigation throughout the year. A water deficit of 5 cm from field capacity is the optimum level at which the depleted available soil moisture could be replenished effectively. It is too early and too late to irrigate when the soil water deficit reaches 2.5 and 7.5 cm   respectively. A single line drip irrigation is economically advantageous because of lower investment in equipment. Tree growth is greatest with sprinkler irrigation   which give better distribution of water than the other systems like drip and under tree spray. There is maximum use of water and fertilizer through roots in the top layer of soil (20 cm) and at 120 cm radial distance to the trunk.

Training and Pruning

During early stage of growth   plants need support which is given with the help of wooden stick fixed near to the stem. Any sprout develop below the bud union is removed as and when it is seen.

Grapefruit trees require less pruning than orange trees   but considerably lesser than lemon trees   because of their natural tendency to spread low   unlike lemons. Under humid tropical conditions   the drooping branches should be pruned to avoid infection by gummosis and foot rot fungi. Due to their more dense foliage and heavier cropping   grapefruit trees give out more dead wood than orange trees. Growers should   therefore   keep this factor in mind while removing the dead wood. The grapefruit should be pruned for the first time to form a foundation framework of the main branches which are well  shaped and balanced may be allowed to remain on the trunk   the rest may be removed and the stubs cleared with pruning shears. The main branches of the tree should be encouraged to arise on the trunk not less than 30 cm and not more than 75 cm above the bud joint.

For the first five years   the trees put out considerable leafy growth. The branches that are more or less obliquely inclined and are fully exposed to the sun are the productive growth arising vertically from high points on the trunk or the main limbs   especially in the centre of the tree (called water sprouts)   should be promptly removed. The cuts made while removing them should be clean and close to the stem. Water sprouts should always be pruned as and when seen.

Pummelo

The pummelo is a monoembryonic in nature. The tree grow up to 3 4 m in height. Leaves are large with broadly winged petiole. Lower surface of the leaf is pubescent particularly the main vein. Fruits are mainly borne singly. Fruits are large sized   subglobose to pyriform in shape   with thick and spongy rind. Fruits are sweet and moderately juicy. Seeds are very large   yellowish wedge shaped   and white from inside. Mainly two varieties white fleshed and red or pink fleshed are available in India. Pummelo is preferred to plant in homestead.

Climate

Pummelo is an essentially tropical citrus fruit. However   it is grown in warm tropical and subtropical climate where rains are fairly received. Pummelos can stand heavy rainfall.

Soil

The soil requirement for pummelo is not very specific   however   soil should be well drained and medium in nutrient contents for better yield.

Varieties

The named varieties of pummelo are:   Kae Pan   of Thailand and   Buntan   of Formosa.

Propagation

Pummelo is a monoembryonic   therefore   it is necessary that it should be propagated by vegetatively. Air layering (marcottage) is commercially adopted method of vegetative propagation. The budded plants of pummelo are usually raised on vigorous rootstock like Jatti khatti and Jambheri.

Planting

It is similar to grapefruit.

Cultural Practices

Almost all cultural practices for raising pummelos are similar to grapefruit.

Harvesting and Yield

The normal season of cropping is from January to March in north India and September to November in South India.

About 100 fruits per tree is the average yield of pummelo.

Insect pests of Citrus Fruits

Lemon Butterfly (Papilio demoleus Linn)

It is the worst leaf destroying pest in nursery. It feeds on almost all citrus species   but has a preference for sweet orange. The tender leaves are attacked from the margin inwards reaching the midrib. Lemon butterfly appears in April and August  September in Punjab. The appearance of this pest in Andhra Pradesh is during July  November   and June  July in Gujarat.

Whiteflies

Among many species   Dialeurodes citri Ashmed whiteflies and Aleurocanthus woglumi Ash   blackflies are the most destructive. The former is a minute in size and pale yellow with dark red eyes whereas the adult of later wooly whiteflies are distinctly more yellow than other. They remain hiding on the under surface of the leaves during day time. Both nymphs and adults suck the sap of leaves and reduce the plant vigour. Severely infested leaves become pale yellow to brown and later they curled and shed. Flowering and fruiting are affected very badly. Whiteflies may encourage the incidence of red scale and which collect under the wool of the whiteflies to avoid light.

As such control of white flies is very difficult. However   in nature   lady bird beetle (Brunus saturalis) feeds on eggs and larvae of citrus whiteflies. Mealy bugs (Pseudococcus spp.) Mealy bugs are polyphagous pest. In citrus species   especially limes   lemons and sweet oranges are main target. Besides   they feed on cactus and begonia. They are most serious pest in many parts of India. The adult female is wingless with a flattened body   having short waxy filaments   while the male is winged with no mouth parts and long antenae and is rarely seen. The nymphs are also covered with white waxy coatings and are amber coloured. The nymphs and adult females suck the sap from the underside of the leaves and at the base of the fruit near the stalk  end. The plant growth is arrested   leaves   flowers and newly set fruits are shed. Ants aid in the spread of the mealy bugs   which are attracted by the honeydew secreted by mealy bugs. The sooty mould develops on honey dew   which adversely affects photosynthesis.

Aphids

Very common species of aphids which attack citrus crops in India are Aphis citricidus Kirk.   Toxoptera citricidus (Kirk)   Myzus persicae Sulzer (peak green aphid)   Toxoptera aurantii Fonscolombe (Citrus black aphid) and T. citricola (Citrus brown aphid)   Aphis gossypii (cotton aphid)   Aphidula pomi de Greer (apple green aphid).

Aphids are found in clusters   over the tender parts of the plant (leaves   new shoots   flower buds). The incidence of aphids is highest in winter and rainy season. They suck the sap from tender parts which fade and become blighted. They also secrete a sweet honey like substance which attracts the ants and develops sooty mould on it. Aphids also act as a vector of virus disease.

Control Measures

Spray the trees with Malathion (0.05%) or phosphamidon (0.025%) or Katin (0.1%) or Rogor (0.3%).

There is no insecticide which can control aphids as vectors of Tristeza virus   because aphids transmit the virus in much shorter time than any insecticide could kill them. They are also migratory in habit and hence defy chemical control.

There are may natural enemies of aphids viz.   lady beetles   syrphid larvae   lace winged flies   any hymenopterus parasites destroy large population of aphids.

Mites

Among several species   red mite (Parate tranychus citri McGrego) is found infesting sweet orange   lemon   grapefruit and acid lime. The green mite (Tetrancychus spp) also infest citrus crops. They feed on leaves   tender fruits and green bark. The underside of leaves are tainted red and the leaves   twigs and fruits get deformed due to sucking of the sap by mites. Severe infestation causes leaf and fruit crop.

Scale Insects

Several species of scale insects are found feelings on citrus. They suck sap from leaves and tender shoots. While sucking sap they inject toxic saliva. Affected twigs dry   leaves and fruits drop down and if fruits remain on the tree   they are in deformed shape. Not only this   sooty mould fungus develops on honeydew excreted by scale insects affecting the photosynthesis activity of the leaves.

The scales are mainly of two types such as armoured and unarmoured or soft scales. Armoured scales secrete a waxy armour which provides protection to them. Unarmoured or soft scales   have tough covering of the body. Armoured scales are : Citrus red scale (Aonidiella aurantii M)   Florida red scale (Chrysomphelus aoniddum L.) Glover  s scale (L. gloverii Pack)   purple scale (Lepidosaphes beckii Newm)   Chaff scale (Parlatoria pergandii Comstock)   whereas unarmoured or soft scales are   cottony cushion scale (Icerya purchasi Maskell)   soft brown scale (Coceus hesperidium L.) Black scale (Saissetia oleoe Bern)   Waxy scale (Ceroptastis floridensis Com.)   White scale (Pinnaspis aspidistrae S). and Arrow head scale (Unaspis yanonensis)

Nematodes

They affect growth of citrus trees by retardation of plant height   size of leaves   number of roots is reduced and later symptoms of tree decline are noticed.

The important nematodes affecting citrus are : citrus root nematode (Tylenchulus semipenetrans Cobb)   Reniform nematode (Rotylenchulus reniformis)   Blurrowing nematode (Radopholus similies Cobb)   lesion nematode (Pratylenchus coffeae T. Goodey)   Root  knot nematode (Meliodogyne afriedane Whitehead) and Lance nematode (Hopdlolaimus indicus Sher).

Citrus Fruit Breeding

During its long history citrus has given the world numerous varieties both by open pollination   bud sports   and of recently by controlled pollination and artificial induction of bud variation. Breeding of superior cultivars possessing desired features is a continuous process throughout the world.

Aims of Citrus Breeding

The general objectives of citrus breeding mainly fall under 3 classes as follows:

Related to Fruit Characters

The prime objective of the citrus breeder is to obtain an excellent desert quality fruit. In addition to this   the fruit should have few or no seeds   suitable shape and size meeting the commercial requirements   good shipping and keeping qualities   attractive rind colour   firm texture to meet the canning industry requirements e.g. grapefruit   citron and oranges   high juice colour for juice and mixed drink purposes and standard vitamin   C   content.

Related to Tree Characters

Compactness   vigour   productiveness   disease and pest resistance   cold hardiness   adaptability to various agroclimatic conditions   congeniality with rootstocks   and better coverage with early   mid and late varieties.

Related to Rootstocks

The obtain rootstock adaptable to different and adverse soil conditions   resistant to trunk and root diseases   high compatibility with the scion and high proportion of nucellar embryony. At the same time to obtain rootstocks which do not impart vigorous growth on the part of scion   so as to make the scion to bear fruits of coarse texture and insipid taste.

 

Time

The citrus seedlings   being perennial   in nature   as a general rule take longer time to come to bearing   usually not less than 5  6 years. However   this period can be reduced to a maximum of half by top   working the seedling on a old tree. Further the trees are too expensive to produce and to test under different agroclimatic conditions.

Polyembryony

Polyembryony is peculiar to citrus. A normal embryo   the resultant of male and female gametes   union   no doubt is present in the seed. In addition to the zygotic embryo   one or more   sometime as many as fifteen   additional embryos developing from the nucellar tissue called   nucellar embryos     are found in the embryo sac. More often the zygotic seedling is crowded out by the vigorous nucellar seedling comes out from a vigorous nucellar seedlings. So even if a seedling comes out from a seed   one is not sure whether it is a zygotic seedling. To obtain large number of hybrids the citrus breeder should select a seed parent known to be either monoembryonic or low in polyembryonic tendency. However   unfortunately all the economic Citrus species are polyembryonic except a few   which greatly restricts their choice and complicate the procedure required to attain the desirable objectives.

Sterility

Sterility is the absence of capacity for gametic or sexual reproduction. Prevalence of high generative sterility is obviously a serious hinderance to the use of a variety in hybridization. Complete pollen sterility is particularly troublesome when   (as in the Navel oranges and the Satsumas) the proportion of nucellar embryos is very high. Sterility often leads to the production of seedlessness. But this unfavourable effect of seedlessness on the fruit setting will be a serious hinderance to the production of valuable new seedless varieties. The general advantage of sterility in citrus is the production of seedless or near  seedless fruits.

Breeding Method

There are four methods of breeding adopted in Citrus   (i) Introduction   (ii) Selection   (iii) Hybridization and (iv) Mutation.

Introduction

This method involves the introduction of types from another region. It is usually attempted when the existing germplasm is felt unsuitable or lack some desirable character or merely to enrich the existing germplasm or to incorporate new blood in the existing germplasm by hybridization. Sometimes to meet the immediate need   as a stop  gap arrangement also this method is adopted. Now  a  days this method is more often employed. A great exchange is going on between different countries.

During the beginning of this century India introduced mainly from U.S.A.   some grapefruit varieties like Marsh Seedless   Duncan   Foster   Thompson   sweet orange varieties like Washington Navel   Valencia   Hamlin   Pineapple etc.   mandarin oranges like Kinnow   Cleopatra   Clementine etc.   lemon varieties like Lisbon   Eureka   Villafranca etc. Even now India is actively considering the introduction of some more exotic types from other countries like Japan   USSR both to enrich the existing germplasm as well to utilize them in hybridization programmes.

Selection

Breeding by selection is a search for superior form   from a lot   without any attempt to control their origin other than by choice of seed parent or choice of a tree as a material for a bud selection. Selection also plays an important role in isolating the superior types from a hybrid populations obtained by hybridization. The variations among citrus have arisen by hybridization   mutations   bud sports etc. From this lot man has selected superior types all through the ages and maintained them under cultivation. The process of such selection has gained considerable impetus with the introduction of vegetative methods of propagation. Even at present this method is employed in selecting superior types as per the objectives by screening from a lot of collected germplasm. This involves the survey of different areas   collection of germplasm   raising the germplasm at a place   studying their performance for a considerable time and finally selecting a superior type.

Hybridization

Planned hybridization   though quite laborious and time consuming   has an important role in solving today  s problems of Citrus Industry in the country. This fact can amply be realised by the performance of a large number of hybrids produced in U.S.A. Essentially hybridization is followed to create new types by reshuffling the genes   in the existing germplasm. For any planned programme of hybridization   a collection of the genetic stock (germplasm) is very essential. The available variations should be located and brought together in one or two centres and utilized for hybridization. Hybridization   essentially involves the controlled crossing of two genetically different parents to obtain a desirable type. In hybridization the breeder has control over the origin of new forms and choice of parents.

Realizing the importance of hybridization improvement of the Citrus varieties   U.S.A. has attempted hybridization on a large scale during the early part of the century and reaped a considerable success in obtaining a good number of promising hybrids. Besides U.S.A.   other countries like USSR   Java   Phillippines   Spain   Australia have also attempted breeding in Citrus with varying success.

Mutation Breeding

This method involves the artificial induction of variation by radiation. Bud variation is an abnormal variation   in stems   leaves   and fruits   that are capable of perpetuation through bud propagation. Such variations arise in the somatic tissues of the plant and frequently are termed as bud sports or bud mutations. Bud variations originate first as single changed cells   which may develop into fruits   limbs or entire tree depending upon the place of origin of such cells. These can be identified by colour   size   shape   texture   rate of growth or other physical characteristics. Many of the fruit variations in the Citrus have been the result of individual fruit variations in otherwise normal trees.

As a rule   the limb variations are usually spotted easily by the appearance of their fruits   but occasionally by characteristic shape   size and colour of the leaves.

Entire tree variations are rather commonly found in old orchards which can be distinguished by their fruit and leaf characters or their habit of growth. Since the fruit is the most important one   most of the entire tree variations have been spotted by their abnormal fruiting characters.

There is ample scope for the citrus breeder to spot out the desired bud variation and perpetuate it vegetatively   notwithstanding the fact that majority of these bud variations are worthless.

Choice of the Procedure

The choice of procedure is very important in the improvement of Citrus varieties. Different procedures have to adopted for achieving different objectives   with different forms. Thus with monoembryonie species like pommelo (Citrus grandis) selfing and crossing of selected parents is advisable   however to create variability X  ray or other such treatments may by adopted. While with polyembryonic varieties the procedure varies with the objective. If new varieties of similar to existing ones are desired   e.g. to prolong the season of variety or to have a variety with less prone to the incidence of granulation   one has to search for probable somatic variation in the variety or group of varieties. On the other hand   if the aim is to produce new varieties   basically different from the existing ones   hybridization between the parents   not closely related   is the best method.

Cytogenetics

Virtually all cultivated forms of Citrus   Fortunella and Poncirus are diploid and the diploid number of chromosomes in these generia is 18.

Blossom Biology in Citrus

Knowledge concerning the blossom biology of Citrus and other related genera is an essential pre  requisite for initiating a hybridization programme. Such knowledge also facilitates the adjustment of cultural operations in relation to flower emergence and fruit development. Blossom biology in Citrus varies with species   variety   place and even within a variety at a given place. Blossom biology constitutes   blooming or flowerings period   flower bud differentiation   flower bud development   inflorescence   sex ratio   anthesis   dehiscence   pollen fertility and stigma receptivity.

Blooming Period

Different species and cultivars may normally have different blooming periods   influenced by agroclimatic conditions. The range of difference among the species grown commercially   however   is comparatively small   normally not exceeding two weeks. The Poncirus and Fortunella flower very late i.e.   in June and July   while most of the Citrus species flower in spring i.e.   in March and April. The lateness of flowering in Poncirus and Fortunella is commonly attributed to their dormancy in winter and late initiation of growth in spring.

The principal blooming period for all commercial species of Citrus is early spring and usually lasts for about 6 weeks. Flowering in India usually occurs mainly from February to April in most of the Citrus species. However   owing to the diversity in climate in India   Citrus species are observed to flower in other seasons also. In North India   where there are distinct winter and summer seasons   the sweet oranges as well as mandarins bloom only once in a year i.e. in March. However   Sinha and Mallik reported that sweet oranges bloom twice in a year under Bihar conditions   first in February  March and next in June  July. Naik reports that Sathgudi oranges in South India flower twice in a year from December to April and September to December depending upon weather conditions. In more even climates of Central and Western India   oranges flower thrice a year at intervals of four months i.e. June   October and February. Coorg mandarins have two distinct flowering periods one during March  April (main season) and the other during September  October (off season).

The lemon   lime and the citron are to some extent continuous bloomers   particularly under tropical climate producing some flowers throughout the year   though the spring bloom is the heaviest. It is not uncommon to find   particularly in lime   flowers   fruitlets   developing fruits and mature fruits all at a given time. In Assam most of the lemon varieties flower throughout the year   while some flower only once in a year. Hill and Rough lemon  are observed to flower only once in a year (March  April)   while Genoa and Seedless lemon flowered early (January) and Nepali oblong flowered latest towards the end of February. Kagzi lime at Varanasi and Kanpur flowers twice once in spring and then in June  July and Naik reported that limes are in harvest throughout the year in South India   with a maximum in March  April and July  September in circars and Rayalaseema   respectively.

Flower Bud Differentiation

Every vegetative bud in Citrus is a potential flower bud. Induction and differentiation are not seen outside   however   under a microscope   differentiation of flower bud can be observed. The vegetative bud in Citrus is conical one with pointed apex. In fact the Citrus buds in general are nearly naked   laking the complex covering of protective scales   generally found in temperate  zone plants. The flower bud has a flattened apex. Flattening and broadening of the shoot apex along with two protuberences one on either side is the first indication of flower bud differentiation. Seven stages of development during the process of differentiation were recognized in sweet orange. Calyx differentiated first   the Corolla then   stamen primordia next and lastly pistil primordia. Cessation of vegetative growth is a pre  requisite for induction. It is generally observed that new flush preceds the flower bud differentiation   ordinarily in early spring.

Abbott reported in Pineapple orange   flower bud differentiation as occurring in January in Florida. In Japan Valencia Late differentiates in late January. Blood Red and Jaffa orange   Kaula mandarin and sweet lime in North India differentiate in January.

Flower Bud Development

In various forms of Citrus the complete development of bud lasts from 18 to 47 days. In sweet orange in North India   a flower bud takes 18 to 22 days while in lemon it took 20  32 days. In sweet lime it takes 22  25 days.

The development of a flower bud in citrus is greatly influenced by the prevailing temperature. As the temperature increases the time taken by a bud to develop is reduced.

Inflorescence

Inflorescence in different Citrus species is of cymose type. Flowers in citrus are borne on two types of shoots   one with leaves and the other without leaves. In true morphological sense   there are no terminal buds in Citrus. The so called terminal bud is nothing but a pseudo  terminal one. Reece called the former one as leafy inflorescence and the latter as leafless inflorescence. Leafy inflorescences are borne on new wood   while leafless inflorescences are borne on oldwood. The distribution and intensity of the two types of inflorescences differ. Zidan reports that in Valencia and Naval oranges and Balady mandarins   the percentage of leafless inflorescence is much more higher than that of leafy inflorescence. Leafy inflorescences are more productive than leafless inflorescences   evidently suggesting that presence of leaves is essential for increased production.

 

Sex Ratio

Citrus produces two types of flowers viz. staminate and hermaphrodite on the same tree with varying intensities. The production of staminate and perfect flowers is greatly influenced by species   season   nutrition etc.

Kagzi lime produces more hermaphrodite flowers than Tahiti lime. In sweet lime the production of staminate flowers is more. Randhawa report low percentage of perfect flowers in different varieties of lemon   except Malta   Meyer and Italian lemons. The occurrence of high proportion of male flowers is seen in lemons and citrons. Higher production of hermaphrodite flowers in sweet orange cultivars is reported by Haribabu.

In the beginning of the flowering period percentage of perfect flowers is higher and gradually the percentage decreases as the season advances in different citrus species. Low temperature and relatively high humidity seem to be more conducive for the higher production of hermaphrodite flowers.

Nutrition also influences the production of perfect flowers. This has been amply demostrated by girdling   ringing and defoliation experiments. A positive correlation exists between the fluctuations of starch content of the shoots and the percentage of perfect flowers. Increased production of perfect flowers is obtained from the normal and shy bearing trees by judicious nitrogen application. Zinc deficiency results in low percentage of perfect flowers.

Leafy inflorescences produce large number of hermaphrodite flowers as compared to leaf less inflorescences.

Anthesis

Ordinarily in citrus the flowers open during the morning time. Many workers have reported that anthesis occurs between 9 A.M. and 12 Noon in citrus. Anthesis is influenced by different factors like temperature   light   position of flower bud   type of inflorescence   aspect of the tree etc. A definite effect of temperature on anthesis in different seasons has been reported but others ruled out the effect of temperature on time of anthesis. Terminal buds open earlier than the lateral buds. Flowers on leafless inflorescences open earlier than those on leafy inflorescence. Flowers on the shaded side of the tree have been observed to open later than those exposed to sunshine.

Dehiscence

Dehiscence of anthers in citrus takes place at different times   in some before anthesis and in others after anthesis. In the former category are included lemons   while sweet oranges   sweet lime etc.   come under the latter group. Low humidity and high temperature are found to influence the dehiscence of anthesis. High temperatures accelerate the dehiscence of anthers.

Stigma Receptivity

Oozing of a gummy substance on the stigmatic surface is the indication of stigma receptivity in citrus. In general the stigma receptivity in various citrus varieties starts 2  3 days earlier to anthesis and lasts 4 to 6 days after anthesis with maximum receptivity on the day of anthesis. Duration of stigma receptivity is influenced by prevailing weather conditions also. In a dry spring it is shorter than in a moist spring.

Storage   Longevity and Fertility of Pollen

The storage and fertility of pollen grains play an important role in hybridization programmes. It is often necessary to store pollen in a fully viable condition so that it may be used subsequently for making crosses between plants whose flowering periods do not coincide. Besides   properly stored pollen can be transported to far off places for utilization for hybridization even in the absence of male parent. Further in fruit trees which are self  incompatible the stored pollen can be artificially applied to get optimum fruit set even in the absence of pollinizers.

Under field conditions the pollen soon loses its viability. However   it can be kept viable for longer periods by proper storage. The citrus pollen dried over concentrated sulphuric acid and sealed in glass vacuum tubes at about 0.5 mm pressure can be kept in a viable condition for more than two months. Trifoliate orange pollen remains viable for 110 days when stored in a desicater over Calcium chloride and remains viable even at   5ºC.

For storage of   Temple   orange pollen   a higher temperature (16ºC) accompanied by a high concentration of CO2 in the atmosphere is found to be ideal   while for Shamouti orange both low temperature and Co2 increase the storage life. Kagzi lime and grapefruit pollen can be kept for 37  38 months at a temperature of 0ºC and 25 per cent RH.

Pollen storage by home freezer can be the most convenient method for storing pollen for short durations.

Certain pollen diluents have been found to be very effective   both in maintaining the viability and subsequently in the operation of pollination. Powdered milk (non fat)   egg albumen and lycopodium are some of the pollen diluents. When pollen is stored with these diluents   the viability is maintained at a higher standard.

Pollen fertility varies from variety to variety. Moreria and Gurgal noted the pollen fertility varying from 0 90 per cent in oranges   50 80 per cent in limes and lemons   above 60 per cent in tangerins and over 80 per cent in grapefruit. They further found that species and forms with the highest degree of polyembryony had a high percentage of viable pollen. Though the converse was not always true.

Pollen Germination

The germination of pollen grains in artificial solutions varies greatly in citrus. Temperature also influences germination.

Nagai studied pollen germination in some varieties of citrus and used 20 per cent solution of canesugar with a trace of Japanese isinglass   the germination ranged from 16 per cent in Valencia to more than 90 per cent in several other varieties. In Morton Citrange   best germinations are obtained with 10 per cent sugar solutions with 58 g of agar  agar in water. The germination of pollen from Meyer lemon in 15 per cent sucrose solution at 20ºC increases by the addition of 2   4 D   thiamin   boric acid and IBA. Randhawa et al. report 15 per cent sugar solution to be the optimum for germination of different lemon and citron pollen. In sweet lime 20 per cent sugar solution gives maximum pollen germination at 28ºC.

Pollination and Fecundation

Self pollination and cross pollination seem to be about equally prevalent and also effective to bring about the formation of embryos and seeds in Citrus.

Natural self pollination in citrus is brought about by contact of anthers with the stigma   by pollen falling or being blown against the stigma or by transfer of pollen by insects. Similarly natural cross pollination is doubtless accomplished by insects (entamophilous).

Fecundation in several species of Citrus occurs about four weeks after pollination. Petal fall and ovary remaining green   are taken as the indications of fruit set in citrus. The success in fruit set is confirmed within 7 10 days after pollination. The intensity of fruit set is influenced by the time of flower opening   type of pollination   type of inflorescence. Early opened flowers have poor chance to set than those which open later. Dhillon further report 12 18 per cent fruit set by open pollination and 65 76 per cent by self pollination in sweet lime. Supplementary pollination and pollination with mixed pollen are reported to enhance the intensity of fruit set in citrus. In leafy inflorescence   fruit set is more than in the leafless inflorescences.

Fruit Development

Citrus fruits develop very slowly   usually taking 6 13 months to reach proper maturity. The duration from set to maturity varies from species to species   cultivar to cultivar   influenced by the condition of the tree   availability of moisture   temperature etc.

Torres reported 9   8½ and 8 month duration for sweet oranges   lemons and mandarins respectively. Motial observed that sour orange took 245 days and Kagzi lime took 106 days for maturity.

Maximum growth of fruits in sweet oranges under Punjab conditions is between 4 and 7 months after set. The growth of fruits in Hamlin and Valencia Late is rapid upto middle of October (8th month) and end of November (9th month) respectively. Subrahmanyam reported active growth in limes accompanied by cell division and enlargement upto 90 days from fruits set   growth lagging between 90  120 days during which the metabolic activities are at their maximum and rapid cell enlargement between 120  180 days.

The fluctuations in growth rates closely parallel the fluctuations in soil moisture. More stable size oranges can be grown under irrigation   provided uniform moisture content is maintained throughout the rapid growth period. Moisture deficit during the period of development   especially if accompanied by high temperatures retards the rate of growth   particularly   in early stages of development.

There is close relationship between the time of flower opening during the blooming period and its ability to grow into a fruit. The flowers opening around the middle of the blooming period have better chance to become fruits than those opening either early or late. The size and growth rate of citrus fruits is closely related with size and number of leaves per fruit on a given branch.

Suitable Climate

Climate is a deciding factor about success or failure of a given crop at a given place. Therefore   one should give utmost importance to it.  Most of the cultivated citrus fruits are indigenous to tropical rain forests of Southern China   Cochin China and certain islands of the Malay Archipelalgo. Broad flat leaves   lack of thickened cuticle limiting transpiration   sunken stomata   weak root hair development   naked buds and absence of a regular dormant period (but cessation of growth is essential) amply demonstrate their origin from the tropical rain forests. Although the Citrus species have originated in the tropical regions   their performance is best in subtropical environment   hence they are mostly categorised under subtropical fruit crops. Nevertheless   commercial citrus cultivation extends right from tropics to temperate regions. The citrus belt of the world covers a wide range of area in latitude. Anywhere within this belt at relatively low attitudes citrus can be grown provided such other conditions like soil and water are favourable. However   the performance of citrus grown under different climatic zones varies accordingly. Fruits from strictly or absolutely tropical zone are usually inferior while those from temperate zones are frequently subjected to low temperatures. On the other hand   the fruits from subtropical regions excel those from other regions. Thus it is clear   that although the range of citrus belt of the world is vast   the actual and strictly optimal area for commercial cultivation of citrus is very much limited.

Influence of Climatic Factors

Temperature

Among the climatic factors   temperature is most potent factor influencing the performance of citrus. Generally speaking citrus endures both maximum and minimum temperatures upto an extent. The endurance varies with different species.

Maximum temperature: The maximum temperature that citrus can endure may be about or slightly higher than 50ºC. Sweet oranges are being successfully grown under temperatures upto 46ºC in Deccan pleatue of India and even upto a temperature of 52ºC In Northern Rajasthan   Western U.P. and Punjab. The maximum temperatures injurious to citrus plants are seldom reached   except in very limited areas. Under higher temperatures leaves   buds   flowers   and young fruits   particulary of lemons and navels   get scorched   while young twigs show injury. The fruits on the outside of the tree camopy   especially of sweet orange and mandarins may get   cooked   to some degree and rendered worthless. Hot summers cause sunburn of fruits in Punjab. When fruit ripens in hot weather it soon passes from maturity to granulation. The injury by extreme temperatures gets aggravated by low humidity and high winds. Fruit set is low under high temperatures at the bloom. Young and newly set fruitlets dry up due to high temperatures. Extreme hot and dry weather during the months of May  June causes shedding of half developed fruits  June drop.

Minimum temperature: Although   the minimum temperature that can be endured by citrus trees varies considerably depending upon the species   varieties   condition of the tree   duration of cold period and other accessory climatic conditions   any temperature below freezing (0ºC) is dangerous   especially when it persists long enough. Thus the tree and fruit might endure a very low temperature (   7ºC or less) for a short period without showing injury   whereas if temperatures from   3º to    4ºC continues for a longer period they are considerably damged. Flowers and young fruits are more sensitive to frost conditions and shed in even very short periods of low temperatures (even slightly below 0ºC). Dormant trees are less prone to frost damage than those which are in active growth phase. Graft and budding areas are more vulnerable to frost.

Frost injury: Webber lists the various Citrus species in a descending order to frost sensitivity thus: Citrus medica (citron) C. aurantifolia (acid lime)   C. limon (lemon)   C. paradisi (grape  fruit)   C. grandis (pummelo). C.sinesis (sweet orange)   C. aurantium (sour orange)   C. reticulata (mandarins)   Fortunella spp. (Kumaquats) and Poncirus trifoliata (Trifoliate orange). The range is thus from the citron of the tropics to trifoliate orange of temperate zone. However   the difference from the species to another is very small   but all are seriously injured if the temperature falls to below   9ºC (3). Even trifoliate orange which is said to be hardiest in most winters   may seriously be injured by early freezes preceded by unusual high temperatures in the early fall. Trifoliate orange requires low temperatures to enter dormancy and high temperatures to break dormancy. Thus it escapes from spring frosts and late winter frosts. Kumquats follow the trifoliate orange. While others like grapefruits   sweet oranges   mandarins and sour oranges get injured by late winter and early spring frosts due to their tendency to start bud growth following a few days of warm weather. Lemons and limes   due to lack of dormancy even   in the winter   are readily subjected to winter injury   as they have new foliage   flowers   and young fruits at almost any time.

The seedlings of sweet orange are able to endure more cold after they have reached bearing age than budlings of the same age. It has also been noted that seedless cultivars are more cold hardy than seedy cultivars. This is attributed to a nutritional phenomenon wherein mineral nutrients are translocated to the developing seeds   thereby leaving the twigs somewhat deficient temporarily.

Very tender foliage or flowers are injured by low temperatures below 0ºC. As the leaves mature   they become less prone to frost injury   probably due to accumulation of mineral nutrients and photosynthates in the leaf tissues. When the tissues reach the freezing point   the fruit gets damaged. They show injury after exposure for shorter periods about two hours to air temperature   2ºC. However   individual fruits vary wildly in this respect depending upon size   location on the tree   rind thickness and initial warmth of the fruit.

Mature and dormant trees have been reported to survive an exposure of 10 hours to low temperature below    4ºC and of one and half hour to   9ºC. Young trees may be killed outright by a single severe cold spell because of their thinner bark and low degree of tissue maturity. Healthy trees   free from mineral deficiencies   pests and diseases   endure cold much better than the unhealthy and weakened ones.

Growth temperatures: The temperature range within which the citrus tree is able to grow   develop and fruit   is 14  40ºC. However   the best growth and performance occurs around 32ºC or within 29  35°C. Fruit maturation   including production of sugars and development of rind colour reach its highest perfection in the lower range of growth temperatures.

The minimum growth temperature required by different species of Citrus varies considerably. Grapefruits require less minimum growth temperature than Calamondin   trifoliate orange   and Citranges. At a maximum temperature of 38ºC   grapefruits performed poorly indicating this temperature as lethal to grapefruits. No growth of any part of the tree occurs at and below the vital temperature viz. 13ºC.

Under more uniform temperatures limes and lemons flower throughout the year with varying intensities   particularly in the coastal areas. However   this tendency is evidently inhibited by high temperatures in the hot interiors.

The amount of heat received during the growth season is more vital than the maximum temperature. A heat unit is taken as a degree above 13ºC daily mean temperature.

If the average daily temperature for a month is 13.3ºC   when the vital temperature of 13ºC   is subtracted from this   0.3ºC is left as a remainder   which on multiplication by the number of days in the month gives the index of total available heat for that particular month. Similarly the heat index is obtained for each month and these added together give the available heat index for the entire growing season of the year.

Heat indices of the growing season have been calculated for some areas in United States as follows: Grapefruit: 5  617  6  781   Washington Navel oranges: 2  706  3  462   Valencia oranges: 2  672   lemons: 1  854. In India no such heat indices are calculated so far except for Allahabad. Allahabad probably has about 5  700 heat units in the warmest six months. While determining the most satisfactory regions for certain varieties   the indices of available heat may be employed.

Relative Humidity

Atmospheric humidity has a greater role in the performance of citrus. In general low humidity gives good colour and external appearance   whereas high humidity favours thin skinned   juicy fruits   which are smaller in size   but high in quality. Citrus fruits grown in partial shade excell those grown without shade in their uniformity in size   smoothness   texture of skin and attraction. Fruits grown near coastal areas tend to be more spherical than those grown in the interior (12). Low humidity promotes transpiration and loss of water   resulting in fruit abscission.

Disease infection is favoured by high humidity. As such desert areas are remarkably free from diseases like gummosis   canker etc.

Rainfall

Proper distribution of rainfall is more important than the total rainfall. An annual rainfall of 500 mm is considered inadequate   while 700 mm rainfall is said to be adequate provided it is favourably distributed. An annual rainfall of 1250 to 1850 mm is generally regarded as sufficient   Unevenly distributed rainfall may be supplemented by additional irrigation despite heavy rainfall. Best quality fruit grows in semiarid   subtropical regions with less than 500 mm of rain   when orchards are irrigated. Under such conditions   especially with warm days and cool nights   the fruit acquires a good colour   even on the tree itself whereas in the humid tropics even ripe fruit remains green. However   heavy rainfall in the two months before harvest influences the quality of citrus fruits by reducing T.S.S. and acidity   as observed by Sanchez in the case of Clementines.

Winds

Exposure to strong winds   whether hot or cool is harmful. Therefore   wind breaks should be provided in windy districts. Heavy gales are harmful to citrus trees and flowers and young fruits are easily blown off   therefore shelter belt trees should be planted in regions where stormy winds are prevalent.

Altitude

Altitude   in general is of importance only as it influences temperature. The great commercial citrus areas of the world are located mainly at moderate elevations ranging from slightly above sea level to 450  750m. In India citrus fruits are grown from sea level to an elevation of 1500 m   in California 700 m   in Spain upto 250 m although in South East Asia trees flourish at altitudes upto 2000 m. Although citrus fruits in tropical countries may be grown at altitudes from sea level upto 1800 m or more   the culture becomes hazardous at such higher elevations.

Climatic Requirements of Different Citrus Species

In general citrus fruits can be grown from temperature to tropical regions under moderate temperatures and rainfall upto an elevation of 2000 m above sea level. However   there is considerable variation among different Citrus species with respect to their climatic requirements.

Sweet Oranges (Citrus Sinensis Osbseck)

Sweet oranges require a dry and arid conditions coupled with distinct summer and winter seasons   with low rainfall   like those available in Punjab   U.P.   Deccan regions of Maharastra   some parts of Gujarat   northern districts of Andhra Pradesh. Under these conditions superior quality of sweet oranges are produced. In an atmosphere of high humidity and heavy rainfall   the sweet oranges produced are of thin and smooth skinned with abundant juice. Such fruits have poor keeping quality and inferior taste. Further under heavy rainfall areas trees are prone to the attack of various diseases and pests. Therefore   the cultivation of sweet oranges should be recommended in the drier and arid regions of India   with a rainfall well under 700  750 mm   with well defined winter and summer seasons and fairly wide variation between the day and night temperatures   for under such conditions the trees grow well and yield fruits of excellent quality.

Mandrin Oranges (Citrus Reticulata Blanco)

Mandarin oranges (Santras) prefer slightly higher elevations and tracts with relatively higher humidity. They grow well in submontane tracts with elevation from 600  1050 m   and rainfall ranging from 75  250 cm. They also grow and fruit well along with sweet oranges in the dry tracts of Deccan at altitudes between 450  750 m   with a rainfall range of 50  75 cm and temperature range of 5  45ºC. One of the largest and most important centres of santra cultivation in India   lies in this area. However   santra does not grow well in the humid plains of South India   Bengal and Bihar at attitude below 300 m. Except in heavy rainfall areas such as Assam   Coorg etc. santras elsewhere are invariably grown under artificial irrigation. Santras tolerate more humidity in summer and winter season than sweet oranges. So they can be grown successfully in all tropical parts of India   as well as   in peninsular India   in the submontane regions of North and Eastern India at elevations between 600 and 1050 m with a rainfall ranging from 75  250 cm.

Acid Lime (Citrus Aurantifolia Swingle)

Acid lime (sour lime   Kagzi lime   Mexican lime) being tenderer to frost than most other citrus fruits   requires tropical climate for its successful performance. Situations which are warm   moderately humid   free from strong winds and frost are ideally suited for its cultivation. It grows successfully even upto elevations of 900 m above sea level   provided the humidity in these regions is not high. In the more humid areas of Assam and West Bengal where the rainfall is above 125 cm   the lime becomes highly suceptible to citrus canker   which makes the trees unproductive and short lived. Commercial cultivation of acid lime becomes risky in Northern India   where the temperatures occasionally fall below the freezing point. Acid limes thrive well in West and South India   where frosts are unknown and the annual rainfall does not exceed an average of 75 cm.

Sweet Lime (Citrus Limettioides Tanaka)

Unlike acid lime   sweet lime can be grown under a wide range of climatic condition. It is more hardy than acid lime and can withstand frost conditions better. It grows well under drier conditions of Northern India than under the equitable climate of South India. It can also be grown successfully at higher altitudes in Assam. Sweet lime is commercially grown in Punjab and Madras while in other parts of India it is limited to home gardens only.

Type of Soil

Soil is an important natural factor which determines the success or failure of a crop. Besides providing anchorage to the plant   soil furnishes water and nutrients for its growth and development.

For good performance citrus requires a deep   well  drained soil   free of excess salts with fair humus content. Though citrus can be grown on practically all types of soils   however   in view of the high oxygen requirements of its roots   light sandy to medium loam soils are considered best.

The effect of following properties of soil on the growth and development of citrus will be helpful in selecting the proper soil for citrus cultivation.

Water Drainage

The citrus may be grown on various types of soils provided the sub  soil drainage is good because water drainage is more important than any other factor   for citrus roots have high requirements of oxygen because of lack of root hairs and accumulation of free water in the root zone results in poor aeration   hindering the root  lets to function. Under prolonged conditions of poor drainage   progressive injury and death of roots occur   leading to decreased performance of the tree as a whole. Resistance of the roots to root  rot and other adverse soil conditions also gets reduced under poor drainage conditions. On the other hand   the performance of citrus is exceedingly well in sandy soils due to good drainage conditions   provided sufficient nutrients are supplied. Sticky heavy soils through which water does not readily percolate should be avoided. Soils situated at lower levels adjoining the banks of irrigation canals   rivers   tanks etc. and those having a higher ground water table within a meter of the surface soil should also be avoided.

Depth of the Soil

Soils for citrus should be quite deep for easy penetration and spread of the root system. Studies have revealed that the roots of orange trees penetrate into the soil quite deep   while most of its feeder roots are situated in the first meter of the soil. As such any soil less than 2 to 3 metres in depth should be discarded. Deep well drained soils with no impervious layers   allow good depth for root development producing trees of standard size   heavy yields and long life. Conversely shallow soils   whether shallow because of hard pan layers in the subsoil or of water table produce substandard trees with short life span and poor yields. At the same time the soil should permit penetration and retention of water upto a depth of 2 meters. Molenaar gives 120 cm as the depth to which citrus will extract available soil moisture from deep well drained soil.

Nature of the Subsoil

Hayes noted that nature of the subsoil is more important than that of a surface soil   because it effects the depth   drainage and fertility of the soil and ultimately the performance of orchard trees.

Soils   with hard pan within 2 metres of the subsoil due to either calcium carbonate concretions or clay should be avoided   as they affect both the permeability and aeration of soils. The depth of the hard pan in the soil often decides the depth of active root system and also the age to which the tree decline starts. Greater the depth of the impregnated layers less is the tree decline. The existence of hard pan or calcium carbonate concretions in the subsoil is responsible for the tree decline in most of the soils of Andhra Pradesh and Punjab. High proportion of calcium carbonate and the presence of hard pan layers are therefore   hazardous for successful citrus cultivation. However   the heavy soils of Nagpur underlaid with a murrum (partly disintegrating rock) layer   which provides a good drainage are quite suitable for citrus cultivation   especially for Nagpur Santra.

Presence of lime in moderate amounts is good for citrus cultivation   as it is though that this helps to the success of orchards. Lime   in moderate amounts as found in orange growing soils of Madhya Pradesh and Deccan   makes the clay soils more friable and fertile. However   soils with large amounts of lime as found in some parts of Deccan   being toxic and harmful to the citrus especially orange trees   should be avoided. A high content of calcium carbonate in citrus soils of Punjab is believed to be an important contributing factor for deficiencies of zinc   iron and manganese. Soils   containing more than 5 per cent per lime in any of the horizon upto 2 metres depth should not be selected for citrus.

Soil reaction

According to experiments conducted in California   a pH value of 5.5 to 6.0 is considered to be an optimum for citrus cultivation   as lower levels tend to increase leaching of lime and magnesium and higher levels are likely to reduce the availability of trace elements. Nevertheless   citrus orchards continue to flourish on soils with pH values of 4.0 to 8.5 and even higher. Haas claims that citrus grow better in an acid than in an alkaline medium. However   it is advised to apply sufficient liming material to prevent the pH value falling below 5.5. It is also advised that the sail pH value of every citrus orchard should be determined once a year.

Salts

Citrus tree health is adversely affected and it succumbs within a few years of planting as a result of malnutrition due to excess salts in the soil. Therefore   soils in which the total concentration of salts exceeds 1000 ppm should be discarded for citrus cultivation. Even irrigation water some times contains high content of salts. So both soils and irrigation water should be tested for their suitability before selection. Kanwar found that soil salinity is one of the important causes of chlorosis in Punjab. Therefore   before planting the trees it would be desirable to have the suitability of the proposed soil tested and appropriate reclamation measures be taken wherever necessary.

Type and Fertility of the Soil

Type and fertility of the soils are not as important as the aforementioned factors in citrus cultivation   so long as the plant nutrients are supplied readily and frequently. However   very light soils lacking fertility and water holding capacity should be avoided. Sandy and gravelly soils are suitable in the higher rainfall areas like the Khasi hills of Assam and Darjeeling for they provide good drainage. Heavy soils   if well drained may produce good crops   but increase the difficulty in cultivation. But stiff   deep black cotton soils of fine texture which crack during summer are not suitable. Presence of high humus content in the soil is also necessary for the effective combination of mycelia and citrus root as they lack root hairs.

The only actually unsuitable soils are heavy clayey soils   extremely dry soils (except   of course   where irrigation is practicable) and most soils with impermeable underground strata retaining stagnant water.

Soils requirement of different citrus species

Sweet oranges and acid limes grow well on a wide variety of soils from heavy clay to very light soils. Heavy soils under good drainage yield bumper crops   while very light soils   on the contrary   due to lack of fertility and moisture produce low yields. In shallow soils the trees remain stunted and die in their prime due to malnutrition. Trees are particularly more sensitive to higher concentration of salts and cannot stand waterlogged conditions for any length of time. The ideal soil thus seems to be a medium or light loam with a slightly heavier subsoil   with a depth of 2  3 meters and pH of 6.0 to 8.0.

Lemons grow and bear well in comparatively shallow soils. However   good aeration upto a depth of a metre or more is more essential for its successful cultivation.

Sweet lime can be grown on a variety of soils and is rather tolerant to defective soil conditions. However   it does best on well drained   deep loam soils.

Other citrus fruits like   grapefruit pummelo grow well on deep well drained   free working sandy loams   loams and silt or clay loams   with the chief preference being for loose   open   sandy loams   with good physical conditions. But heavy soils containing high percentage of clay which have a tendency to drain poorly and insufficient aeration are not suitable.

The most distinctive feature of pummelo is its relatively high tolerance to saline conditions   which has been exploited in Thailand   wherein pummelo is cultivated in unproductive coastal low lands around river belts and brackish marshy areas. It is believed in Thailand that the flavour and the quality of the fruit are enhanced by the salt   though lacks experimental proof. This must be investigated and if found true   then pummelo becomes a potential crop for coastal low lands   particularly in tropical countries   where climate   moisture and salinity prevent the cultivation of other citrus fruits.

Mandarins grow on a wide variety of soils   but ideal soil seems to be a medium or light loam with a slightly heavier subsoil. Shallow soils should be avoided. Rain fed santras tolerate more soil acidity upto pH4 but a range of 5  8 is more ideal.

Citrus soils of India

Citrus fruits are grown on a variety of soils throughout the length and breadth of India   right from sandy soils on the coastal areas to deep black soils of interior   alluvial soils of Indo  Gengetic plains to laterite gravelly soils on hill slopes of Assam   Coorg and Wynad.

In Nagpur area mandarins are grown on a variety of soils. The typical black clay soils   which crack on drying are quite common. The other types are medium black to brownish in colour with different textures. The soils in general are very shallow   with a depth varying from a quarter of metre to more than a metre and are underlaid with a porus subsoil of murrum. As the soils are shallow   frequent application of manures and fertilizers is highly essential to maintain high productivity levels. Evidently   the world famous Nagpur Santra performs excellently under such soil and subsoil conditions   under which conditions the tight skinned oranges perform poorly due to micronutrient deficiencies. The pH of the soil ranges from 7.0 to 9.0.

In Coorg and Wynad tracts of South  India   Santras flourish well in deep but well drained black and red loamy soils.

In Assam   Khasi orange is grown in valley lands of submountane areas where the soils are of alluvial types and on the hills   where the soils are mostly lateritic. Major citrus growing belts of Assam are sandy loam or clayey loam soil with pH 4.5 to 6.0 and with high organic matter content.

In punjab and western Uttar Pradesh the citrus fruits are grown on Indo  Gangetic alluvial soils ranging from light to heavy.

In Andhra Pradesh   citrus fruits  mainly sweet oranges and acid limes are grown on a variety of soils   on deep and shallow soils with rock or hard pan at subsoil level. The pH ranges from 6.5 to 8.8. The soils are poorly drained and have other setbacks. Citrus is grown even under unfavourable conditions   e.g. in Kurnool district. Although Naik condemned this area as unsuitable for citrus   many growers feel that citrus in this area is more remunerative than any other crop. The same trend is followed in Anantpur district   where citrus is indescriminately planted in all types of shallow soils   with meagre water sources. Yet many grower make reasonable profits from citrus orchards in these areas.

Citrus Soils of Flsewhere

In California the soils of different section are variable ranging from light sandy to heavy clay loams and in general are fairly productive. In Florida citrus fruits are grown on fine sandy loams which were originally occupied by native forests of hard woods   oaks etc. (Hammocks) and are frequently on the banks of rivers and lakes   on very sandy soils ranging from fine sands and sandy loams to coarse sands underlaid with clay (high pine lands) and on soils which are very shallow and underlain with lime stone rock (flat woods). In general the soils of Florida are acid.

In china   citrus soils in general are sandy loams varying to clay loams. In locations   where the soils are well drained   the trees suffer from drought in the dry season. In other locations on level lands the trees are often planted on raised beds with drainage ditches between the rows to remove the excess water during heavy rains. The principal part of commercial citrus crop in china is produced in low lands   adjacent to rice fields and sea where the tide water fills the ditches between the rows   with very high water table.

In Japan most of the citrus orchards are on hill slopes. The nature of the soil varies from sandy soil of granite origin to clay soil. With low natural fertility   soil are acidic in reaction. To offset coldness in winter   citrus fruits are grown on shallow and poor soils   under heavy fertilization.           

When compared to other countries like U.S.A.   USSR etc. the citrus breeding in India has started late and the work so far has not given any considerable success as in other countries.

Work done in India

At Poona   College of Agriculture   first attempts were made at hybridization in 1912   1914 and 1918   however   no success both for stock and scion   for soil and climate adoptability   was obtained. Afterwards   there was a long gap in citrus breeding in India. However   it was again initiated somewhere in 50  s. But no published information on the objectives   progress and achievements of citrus breeding in India are available   except sporadic references here and there.

In order to achieve the above objects   crosses between cultivars (local and exotic) of same species   between different species (sweet orange and pummelo and lemon   lime and lemon) and between different genera (C. sinensis and Feronia limonia   Atlantia monophylla Fortunella spp.) were affected.

A large number of hybrid progenies were obtained as a result of the above crosses and these hybrid progenies were planted in the main field for studying their performance.

Among the lemon hybrid progenies which came to bearing within 2  3 years from planting 5 hybrids were described by Rangacharlu. However   afterwards there were no published reports about the performance of the hybrid progenies   not any indication of continuing the citrus hybridization programme at Kodur.

Bindra reported that out of 10 root  stocks screened against citrus nematode Tylenchulus semipenetrens   trifoliate orange and Savage orange   (a hybrid between Poncirus trifoliata × Citrus sinensis) proved best.

At Citrus Experiment Station   Chetheli   Coorg   work on breeding for rootstock improvement is being carried out. From screening of Citrus germplasm   trifoliate orange and sour orange appeared to be resistant to Phytophthora. Crosses were made taking Rough Lemon   Rangpur Lime   Cleopatra mandarin  . Kodai Kitheli   Kichili and Coorg mandarin as seed parents and Poncirus trifoliata as pollen parent. On screening of the hybrids and nucellar seedlings it was observed that all hybrids were resistant to Phytophthora while nucellar seedlings showed different degrees of susceptibility upon seed parents   thereby showing that trifoliata imparts resistance to hybrids. At Saharanpur   experiments conducted for the last two decades revealed that the Hill lemon rootstock proved most compatible for Mosambi   pummelo for Kagzi lime   Italian 76 for Hill and Florida Rough for Rangtra mandarins.