1. ORIGIN, EVOLUTION, HISTORY AND SPREAD OF POTATO
Introduction, Origin, Archaeological Evidence, Historical Evidence, Evolution, History, Early History, Spread in Europe, Spread in Asia, Africa, etc., Spread in India

2. BACTERIAL DISEASES OF POTATO AND THEIR MANAGEMENT
Bacterial Wilt/Brown Rot, Distribution, Etiology, Diagnostics and Detection, Management, Avoidance, Soft Rot or Black Leg

3. POST HARVEST HANDLING OF POTATO
Significance, Post Harvest Losses, Enhancement of Shelf-Life of Potato Tuber, Avoid Mechanical Tuber Damage Including Internal Bruising, Sorting and Grading of Tubers, Wound Healing and Curing, Weight Loss, Dormancy, Storage Temperature, Treatment of Tubers Against Diseases and Insect, Use of Growth Regulators Against Sprouting, Regulation of Sprouting in Stored Potato, Pre-harvest Application for Sprout Suppression, Post Harvest Application for Sprout Suppressions, Mode of Application, Storage, Controlled And Modified Atmosphere Storage of Potato, Other Storage Methods of Potato, Improvised Country Storage, Low Cost Zero Energy Cool Storage, Kucha Mud House or Room Storage, Pit Storage, Viability of Stored Potato Seed, Gamma-Irradiation, Change in Composition During Storage, Percentage Dry Matter, Carbo-hydrates, Phenolic Compounds, Glycoalkaloids, Vitamins, Processing, Morphological Characters, Chemical Composition, Dry Matter, Reducing Sugar Content, Varieties for Processing, Practical Aspect of Potato Processing, Grading, Cleaning, Peeling, Cutting/Slicing, Blanching/Cooking, Frying, Dehydra-tion, Cooling/Freezing, Sterilization, Packaging, Popular Potato Products, Potato Flakes and Granules, Potato Dice, Potato Chips, French Fries, Canned Potatoes

4. BIOTECHNOLOGY FOR PRODUCTION OF QUALITY PLANTING MATERIAL
Meristem Culture, Thermotherapy, Chemotherapy, Electrotherapy, Virus Detection and Diagnosis, Micropropagation, Micropropagation in Virus-Free Potato Seed Production, Conclusion

5. BREEDING FOR PROCESSING VARIETIES
Potato Products, Quality Requirements for Processing, Morphological, Size and Shape, Defects, Biochemical, Dry Matter, Reducing Sugars, Phenols, Inheritance, Morphological Attributes, Tuber Shape, Growth Cracks, Hollow Heart, Internal Rust Spots, Greening, Biochemical Attributes, Glycoalkaloids, Dry Matter, Reducing Sugars, Enzymic Browning, Development of Varieties for Processing

6. TRUE POTATO SEED TECHNOLOGY
Role of TPS Populations, Potential and Advantages of TPS Technology, Constraints/Shortcomings in the Adoption of TPS Technology, Early History, Priority Areas for TPS Dissemination, Economics of TPS Technology, Agronomy of True Potato Seed (TPS), Utilization of TPS for Potato Production, Substrate Composition and Preparation of Nursery Beds, TPS Sowing, Production of Seedlings for Transplanting, Production of Seedling Tubers, Field Preparation, Crop from Seedling Transplanting, Crop from Seedling Tubers, Crop from Seed Broadcasting, Identification Of Suitable TPS Families, Breeding of TPS Populations, Breeding Requirements for TPS, Parental Lines, Flowering, Production and Fertility of Pollen, Berry/Seed Formation, Production of Hybrid TPS, Planting of Hybridization Block, Hybridization, Harvesting of Berries and Seed Extraction, Processing, Packaging And Storage of TPS, Dormancy in TPS, Evaluation and Selection of TPS Populations, Utilization of TPS for Potato Production, TPS Populations Released, Future Strategies

7. SEED PRODUCTION
Seed Potatoes, Variety, Diseases, Degeneration, Seed Plot Technique, Selection and Preparation of Field, Seed, Thermotherapy, Planting, Seed Size and Spacing, Time of Planting, Fertilization, Irrigation, Weed Control, Roguing and Inspection, Haulm Cutting, Aphid Management, Disease and Pest Management, Harvesting and Storage, Seed Treatment, Impact of the Technique, True Potato Seed (Botanical Seed), Production of Hybrid TPS, Hybridization, Seed Extraction and Storage, Crop Production Through TPS, Nursery, Development of Virus Free Seed of Potato and Testing for Viruses, Selection of Healthy Seed, Sanitation, Meristem TIP Culture, Chemical Treatment, Reduction in Vector Population, Testing of Potato Viruses, Conventional Methods, Advanced Methods, Elisa Test, Advantage of Elisa, Maintenance of Virus Tested Foundations, Potato Biotechnology, Elimination of Pathogen through Meristem Culture, Potato Meristem Culture, Establishment of in Vitro Cultures, From Infected Plants, from Infected Tubers, Steps involved in Potato Meristem Culture, Meristem Tipculture, Micro Propagation of Mericlones:, Micro Tuber Production, Production of Micro Tubers, Production of Normal Tubers, Synthetic (Artificial) Seed, Seed Certification, Methods of Inspection for Certification, Tagging, Content of Breeder Seed Bag, Seed Certification Standards, Quality Control, Objective, Sampling, Procedure of Grow Out Test

8. PHYSIOLOGICAL DISORDERS
Tuber Cracking, Tuber Malformation or Deformities, Surface Abrasions or Feathering, Hollow Heart, Greening, Black Heart, Low Temperature Injury, Sunscalding, Aerial Tubers

9. FAVOURABLE CONDITIONS OF GROWTH FOR POTATO
Climate, Rainfall, Temperature, Light, Soil, Topography, Economical Condition, Capital, Labour

10. CULTIVATION
Land Preparation, Preparatory Tillage, Primary Tillage or Ploughing, Country Plough, Mould Board Plough, Bose Plough, Disc Plough, Spade, Tractor, Power Tiller, Secondary Tillage, Ladder or Plank, Harrow, Cultivator, After Tillage, Planting of Potato, Sowing Time, Selection of Seeds, Source of Seed-Tubers for Commercial Use, Seed Stored in Country Cellers, Seed Stored in the Cold Storage, Seed Produced in the Hill Areas, Dormancy of Seed Potatoes, Varieties with Short Dormancy Period, Varieties with Medium Dormancy Period, Varieties with Long Dormancy Period, Breaking of Dormancy, Mechanical Method, Heating of Seed Tubers, Cutting of Seed Tubers, Peeling of Seed Tubers, Chemical Method, Correct Size and Weight of Seed Tubers, Seed Treatment, Seed Rate, Method of Planting, Flat Bed Planting, Planting in Furrows, Planting on Ridges, Pit Method, Spacing, Potato Planting Equipments, Tractor Drawn Fertilizer Drill Cum Line Marker, Tractor Drawn Potato Planter Cum Fertilizer Application, Two Row Space Marker-Cum-Ridger, Potato Planters, Hand Fed Potato Planter, Corrective Type Potato Planter

11. MANURING
Manures, Compost, Rural Compost or Village Compost, Urban Compost or Town Compost, Farm Yard Manure (F.Y.M.), Oil Cakes, Edible Oil Cakes, Non-edible
Oil Cake, Green Manure, Fertilizers, Nitrogenous Fertilizers, Phosphatic Fertilizers, Potassic Fertilizers, Role of Nutrients in Potato, Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulphur, Zinc, Iron, Manganese, Copper, Micronutrient, Doses of Fertilizers, Method and Time of Application, For the Hills, For the Plains, Autumn Crop, Spring Crop

12. HARVESTING
Early Crop, Main Crop, Method of Harvesting, Animal Drawn Single-row Potato Digger, Two-row-tractor Mounted Potato Digger, Potato Elevator Digger, Potato Spinner Digger, Grading, Marketing, Transport, Storage, Method of Storage, Country Method of Storage, Room Storage, Pit Storage, Heap Storage, Factors Influencing The Storage Behaviour, Variety, Time of Harvest,
Size of Tubers, Cultural Practices, Cold Storage, Physiological Changes During Storage, Periderm Formation, Starch-Sugar Balance, Sprouting, Yield

13. FUNGAL DISEASES AND THEIR MANAGEMENT
Late Blight, Symptoms, Distribution And Losses, Pathogen, Variability, Survivability, Genetics and Cytogenetics, Epidemiology, Sources of Inoculum, Environment and Disease, Disease Spread and Build Up, Management, Chemical, Cultural Practices, Early and Phoma Blight, Symptoms, Distribution, Epidemiology, Management, Cercospora Leaf Spots, Symptoms, Distribution and Crop Losses, Epidemiology, Management, Soil and Tuber Borne Diseases, Black Scurf and Stem Canker, Symptoms, Pathogen, Epidemiology, Management, Powdery Scab, Symptoms, Pathogen, Etiology and Epidemiology, Management, Charcoal Rot, Wart, Minor Diseases, Fungal Wilts, Tuber Rots, Storage Diseases, Dry Rots

14. LOW INPUT TECHNOLOGY FOR POTATO   PRODUCTION
Input Intensiveness of Potato Cultivation, Seed, Cultural Operations, Manures and Fertilizers, Weed Management, Towards Low Input Technology for Potato Production, Tillage, Seed, Fertilizers, Irrigation, Weed Control, Pests and Diseases Control, Organic Farming as a Method of Low Input Technology

15. MICRO-NUTRIENT REQUIREMENTS OF POTATO
Effect of Micro-nutrients on Growth and Yield of Potato, Diagnosis of Micro-nutrient Deficiencies in Soils and Plants, Visual Diagnosis, Deficiency Symptoms, Iron, Manganese, Copper, Boron, Molybdenum, Plant Analysis, Soil Analysis, Micro-nutrient Deficiency in Potato Growing Areas, Response of Potato to Micro-Nutrients, Factors Affecting Response of Potato to Micro-nutrients, Root and Shoot Parameters of Cultivars, Micro-nutrients and Quality of Potato Tubers, Amelioration of Micro-nutrient Deficiencies, Methods of Micro-nutrient Application, Time of Application, Sources of Micro-nutrients

16. WEED MANAGEMENT
Methods of Weed Management, Non-Chemical Methods, Crop Rotation, Summer Polughing, Placement of Fertilizers, Mechanical Control, Chemical Methods, Efficient Use of Herbicides, Calibration, Calculation of Herbicides for Application, Integrated Weed Management, Mulching, Effect of Herbicides on Quality of Potato, Dry Matter, Starch, Protein

17. ORGANIC FARMING
Concept, Definition and Components, Value of Organic Amendments and Soil Conditioners, Bulky Organic Manurers, Green Manures, Concentrated Organic Manures, Crop residues, Bio-fertilizers, Vermicompost, Crop and Soil Management, Legume based Crop Rotations, Phytosanitary Crop Rotation, Green Manuring, Agricultural Waste Incorporation in Soil, Agricultural Biopesticides, Sustainable Integrated Nutrient Management, Chemical Fertilizers, Organic Manures, Bio-fertilizers, Green Manuring, Crop Yield and Quality
18. CROPPING SYSTEMS
Sustainable Systems, Potato in Relation to Goals of Sustainable Cropping Systems, Strengths of Potato in Multiple/Inter-Cropping Systems, Potato Based Cropping Systems in Different Agri-zones, North-Western Plains, Western and Central Indo-Gangetic Plains, Eastern Gangetic Plains, Plateau Region, North-Western Hills, North-Eastern Hills, Southern-Hills, Implications and Future Thrusts

19. BIOLOGICAL AND SEROLOGICAL DIAGNOSIS OF POTATO VIRUSES
Chloroplast/Slide Agglutination Test (Sat), Micro-precipitin Test, Agar Double-Diffusion Test, Latex-agglutination Test, Enzyme-linked Immunosorbent Assay (ELISA), das-ELISA, Indirect ELISA, Dot-ELISA (dot Immunobinding ELISA), Tissue Blotting and Tissue Squashes, Immuno Electron Microscopy (IEM)

20. POTATO PESTS AND THEIR MANAGEMENT
Soil Pests, Cutworms, Distribution, Nature of Damage, Population Dynamics and Biology, Management, Cultural and Mechanical, Chemical, Biological, Integrated Management, White Grubs, Management, Minor Soil Pests, Foliage Feeders or Defoliating Pests, Defoliating Caterpillars, Distribution, Nature of Damage, Population Dynamics and Biology, Management,
Epilachna Beetles, Minor Defoliating Pests, Sucking Pest or Sap Feeders, Aphids, Management, Cultural and Mechanical, Leaf hoppers, Broad Mite, Other Minor Sucking Pests or Sap Feeders, Storage Pests, Potato Tuber Moth, Nematode Pests of Potato, Potato Cyst Nematode (PCN), Root Knot Nematode, Cultural Practices


21. POTATO STORAGE
Dormancy, Post-harvest Losses, Physiological Losses, Effect of Temperature, Effect of Relative Humidity, Pathogenic Losses, Storage Methods, Refrigerated Storage, Non-refrigerated Storage of Potatoes, Evaporatively Cooled Potato Store, On-Farm Storage, Sprout Inhibitors, Tetrachloro-Nitrobenzene (TCNB), Maleic Hydrazide (MH), Isopropyl-N-3-Chlorophenyl Carbamate (CIPC), Natural Substances as Sprout inhibitors, Irradiation, Biochemical Changes during Storage, Changes in Carbohydrates, Changes in Nitrogen Fractions, Changes in Enzyme systems, other Biochemical Changes

22. POTATO PROCESSING
History, Areas Suitable for Growing Processing Potatoes, Processing Quality of Indian Potato Varieties, Processed Potato Products, Dehydrated Products - Village Level, Potato chips, French Fries and Flakes - Commercial Production, Grading, Sorting and Washings, Peelingr, Washing, Sorting and Trimming, Chips, French Fries, Flakes, Starch, Other Edible Products, Potato Custard Powder, Soup or Gravy Thickener, Potato Biscuits, Potato Papad, Potato Sticks or Shreds, Chakali, Vada, Alu Bhujiya,

23. STACKABLE POTATO CHIPS TECHNOLOGY
Introduction, Experimental Work, Main Raw Material Characterization, Press Releases, Viscosity Profiles, Dosing Step, Mixing Step, Sheeting Step, Cutting
and Rework Handling, Experimental Work Conclusions, Other Process Steps, Frying and Moulding, Seasoning Device, Portioning and Packaging:

24. POTATO
Scientific Name and Introduction, Quality Characteristics and Criteria, Horticultural Maturity Indices, Grades, Sizes and Packaging, Optimum Storage Conditions, Controlled Atmosphere (CA) Conditions, Retail Outlet Display Considerations, Ethylene Production and Sensitivity, Physiological Disorders, Postharvest Pathology, Quarantine Issues, Suitability as Fresh-cut Product, Special Considerations

25. TREATMENT AND DISPOSAL OF POTATO WASTES
Pollution, Terminology, Testing, Regulations, History, Characteristics of Processing Plant Effluents, Components of Potato-Processing Waste, Effect of Process, Design of Effluent Treatment Facilities, Waste Treatment Processes, In-Plant Treatment, Screening (Pretreatment), Primary Treatment, Secondary Treatment. Biological Filters, Anaerobic Systems, Solids Disposal, Advanced Wastewater Treatment, Filtration, Other Treatment Methods, Application in Potato-processing, Municipal Treatment

26. ADVANCED THERMAL APPLICATIONS IN POTATO PROCESSING
Storage, Peeling, Preheating, Blanching, Dryers, Rotary Drum Using Radial Nozzles, Convection Drying, Impingement Roaster, Conveyor Dryers, Spray and Flash Drying, Fryers, Vacuum Frying, Radio Frequency, Freezing Technology, Adsorption Chiller, Waste Treatment, Sanitation, Energy Recovery, Belt Cooker, For Steam-cooking of Potatoes and Roots


27. SNACK CHIP DEEP FAT FRYING
Process Description, Emissions and Controls, Emissions, Controls

28. TROIKA POTATO CHIPS
Business Plan, Summary, The Enterprise, General Information, Contributed Capital, Appraising Market Value of Stockholders’ Equity, Decision Making,
Profit Sharing, The Product, Analysis of Market and Competition, Marketing and Pricing Strategy, Organization of the Production Process, Risk Factors, Financing and Distribution of Profits, Financial Planning, Appendix, Cultural and Sociological Notes, The Russian Sense of Time, Openness Versus Secrecy, Obedience Versus Autonomy, Attitude toward Law and Contracts, The Importance of Relationships, Organized Crime, Working with Russian Partners

29. MANUFACTURE, STORAGE AND TRANSPORT OF FROZEN FRENCH FRIES
Importance of Frozen Potato Products, Types of Frozen Products, Desirable Characteristics of Processing Potato Varieties, Effects of Crop Production Inputs on Processing Quality, Harvest, Storage, Processing, Frozen Product Storage,
Transportation, Preparation for Final Cooking and Consumption

30. GRADING MANUAL FOR FROZEN FRENCH FRIED POTATOES
For Frozen French Fried Potatoes, Areas of Production, Varieties, Receiving, Determining the Quality and Condition of Raw Potatoes for Frying Purposes, Determining the Quality and Condition of Raw Potatoes for Frying Purposes, Manufacture, Washing, Manufacture, Peeling, Trimming, Slicing, Sizing, By-Products, Desugaring, Blanching, Frying, Fat or Oil, Time and Temperature, Packaging, Inspection During Packing Operations, Inspecting the Product, Sample Unit Size, In Retail Type , In Institutional Type, Fry Color, Fry Color of the Individual Units, Fry Color of the Sample Unit, Fry Color Designation of a Sample Unit, Re-fry Color, Re-fry Color of the Sample Unit, Re-fry Color Designation, Types, Styles, Strips, Length Designations, Determining the Length, Minimum Equipment for Inspecting Frozen French Fried Potatoes, Preparation of Sample, Quality Evaluation, Grade Factors Which are not Scored Flavor, Color Designation of a Sample Unit, Grade A, Good Color, Grade B Reasonably Good Color, Substandard, Uniformity of Size and Symmetry, Grade A, Grade B, Considerations, Defect Tables in the Standards, Assigning the Score for Defects Procedure, Texture, Heating the Product, Oven Method, Deep Fat Method, Sogginess, Hardness, Pull Away, Crisp Outer Surface, Sugary Ends, Excessive Oiliness, Score Points, Scoring Procedure, Certification, Special Instructions, Fry Color Classification, Type, Style, Length Designations, Requests for Specific Certificate Information, Procedure

31. PERFORMANCE ENGINEERED FRYING AND FILTRATION SYSTEMS
SF Series Oil Filter, Consumers Love Coated, Proven Fryers and Filters, Maintaining Cooking Oil Quality, Long-Term Process Productivity, LINK is Comprised of Four Distinct Modules, Productivity Relies on Effective Filtration, An Unlimited Menu of Coated Products, Fryer Heat Method Comparison Analysis, Direct Heat - Direct Fired, Key Advantage, Key Disadvantages Direct Heat- Indirect Fired, Key Advantage, Key Disadvantages

32. COST EFFICIENCIES IN SNACK
FOOD PROCESSING
Highlights, Sector Overview, Company Description, The Situation, Audit Findings, Humpty Dumpty’s Path to Innovation and Profitability, 2nd Stage R&D Study, Implementation Status, Drivers for Change, Implications to the Food Sector, Food Industry Cost Reduction Program, Ontario Ministry of Agriculture and Food (OMAF)

33. LATEST RADIX POTATO FLAKE SORTER
INSTALLATION EXCEEDS EXPECTATION”

34. T H E R M A L P R O C E S S I N G S Y S T E M S F O R   P O T A T O E S
The Experience You Need, The Excellence You Deserve, Satisfying Customer Performance and Profit Objectives, Testing and Research, Computer Aided Design and Manufacturing, Turnkey Installation, A World Renowned Service Organization, Choose From these Accessories & Options to Customize Your National Installation, Apron Cleaning Devices. Feed/Discharge Equipment, Other Options, National Offers a Complete Line of Thermal Processing Equipment to Meet the Needs of the Potato Industry, Conveyor Preheater, Two-Stage/ Tri-Mode Belt Blancher, Bi-Mode Dextrose System, Conveyor Dryers & Equilibration Systems, The Seal-Welded Modular Dryer(SWMD)

35. THE POTATO SYSTEM IN WEST JAVA, INDONESIA
Abstract, Acknowledgments, The Potato System
In West Java, Indonesia, Introduction, General Considerations, Methods and Procedures, Potato Production, Present Situation and Trend in production, Cultural Practices, Cost and Benefit, and Institutional Aspects, Conclusions and Issues for Further Research, Potato Marketing, General marketing Situation and Trend in Price of Potatoes, Marketing of Ware Potato, Potato Seed, and Processing Potato, Ware Potato Marketing, Sorting and Grading, Marketing Channels, Field Petty Assembly Traders, Contract traders, Rural Assembly Traders, Regional/Inter-Regional Traders, Wholesalers, Retailers, Marketing Margins, Potato Seed Marketing, Marketing Channels and Marketing Margins for Potato Seed, Marketing of Potatoes as Raw Material for Chips, Conclusions, Potato Processing, Large-Scale Potato Chips Processing, Small-Scale Potato Chips Processing, Conclusions, Consumer Preferences for Potato Chips, Consumer Preferences by Income Group: Results of a Household Survey, Panel Survey of Acceptance of Several Potato Chip Products, Conclusions, Conclusions and Recommendations

36. SCREW BLANCHER FOR POTATO PROCESSING
The equipment, The advantages, Technical Data Screw Blancher

37. PREWASHER WITH CYCLONE DESTONER
FOR POTATO PROCESSING
The Process, The equipment, The advantages, Technical Data, Prewasher

38. BATCH FRYER
Automatically Produce Consistently Uniform Kettle Style Potato Chips, Up to 360 lbs/hr or More, Superior Oil quality, Oil Level Control, Ready to Run, Automatic Slice Stirring, Full PLC control, Easy Cleaning, Optional Features

39. BOOSTER HEATER
Utilize Wasted Exhaust Heat, Boost Output & Save Fuel, Uniform Heat Transfer, Self-Cleaning Tubing, Multi-Layer Insulation, Rugged Construction, Booster Heater Model BH

^ Top

 

Origin, Evolution, History and Spread of Potato 

INTRODUCTION

Potato rightly called, “the vegetable that changed history” provided both the spark and the fuel for centuries to the social change. While conquering the world, it was banned and lauded, cursed and praised, feared and loved until humanity welcomed it into its home and hearth. Today, as one of the world’s major non-cereal food crop, potato is grown in more than 148 countries in a wide variety of soils and climates surpassed only by wheat, rice and maize in total production. Yet till 16'h century it was unknown to the people of Europe, Asia, Africa and North America. The crop has a fascinating history of its origin, evolution and spread in the world, stretching to nearly 7000 to 9000 years back. Some of it is well documented while other has been chronicled from the archaeological remains and historical evidences.

ORIGIN

The potatoes of the South America, where it grows wild in nature, present the widest diversity of forms in tuber shape, size, colour, taste, etc. indicating its origin in South American continent. The main cultivated potato species Solanum tuberosum L., a tetraploid (2n=4x=48) is believed to have originated from Andes of Peru and Bolivia in South America, more specifically in the basin of lake Titicaca on Peru-Bolivian borders, from its wild diploid ancestors many of which may be extinct now. Two main centres of diversity of tuber bearing Solanum species are Central America and Andean region of north-western Argentina. Peru and southern Bolivia. The species grow in a wide variety of habitats from semi-desert conditions of northern Argentina, southern Bolivia and Mexico to the high rainfall subtropical forests of Central and South-America. Thus potato shows a wide adaptation to altitudes right from the sea level to nearly 5000 masl.

Archaeological evidence

Spectacular and beautiful ceramics were excavated dating from the Moche cultures in northern Peru (c. AD 1-600) and the Chimu peoples (c. AD 900-1450), as well as. Huari or Pacheco urns from the Nazca valley in southern Peru (c. AD 650-700). These ceramics, depicting many forms of potatoes, were from coastal areas. Therefore, it is presumed that the potters obtained potatoes by barter or other means from farmers in the highlands where potatoes were actually ‘cultivated’. Surprisingly these ceramics are restricted to Peru, and none was recovered from Colombia. Ecuador, Bolivia, Argentina or Chile, even though the potato is certain to have been an ancient crop in these countries also. Actual remains of the potatoes were also recovered infrequently from tombs, dwellings and rubbish heaps including chuno or tunta, from some archaeological sites. Archaeological remains of potatoes from the Chilca valley near Lima have been radiocarbon-dated to 7000 years before present. There is much later evidence from rubbish heaps, graves and food stores of potato cultivation at 4500 to 3500 years before present.

The Chilca valley evidence based on excavations in Mexico and elsewhere takes the origin of potato cultivation back to an age when maize first became cultivated crop in Mexico and places it with the approximate time of agricultural origin in the New World. From studies between these old potatoes and the distribution of existing primitive cultivated potatoes and the wild species most similar to them, it seems highly probable that the first ever potatoes were cultivated in the northern Bolivian region of Lake Titicaca/Lake Poopo.

Historical evidence

The conqueror of Peru, Francisco Pizarro, may well have been the first European to see potatoes in 1533, but there is no actual (historical) record of this event. The first historical record is of 1537 when a band of Spaniards led by Jimenez de Quesada penetrated into the highlands of what is now Colombia. This was followed by accounts of Lopez de Gomara for potatoes in southern Peru and by Pedro Cieza de Leon in the area of what is now southern Colombia and northern Ecuador. Potatoes in Chile received first mention by Sir Francis Drake in 1578.

The native names of the potato also indicate its ancient and widespread cultivation, since they differ completely from the main Red Indian languages that were spoken in the areas where the potato was first growing. Thus in the Chibcha language of Central Colombia the names iomza, iomuy, etc. were used: in Quechua, the language of the Inca Empire, the usual name was papa. In Bolivia, the Aymara Indians used the words amka and choque, whilst in Chile, the Araucanians gave it the name poni. The Spaniards adopted the name papa for the potato, which was used throughout their south American colonies. In Europe, neither batata nor papa for potato was ever adopted because the Spaniards first encountered sweet potato, and not having a name for a similar tuber, they used the Indian word batata. Subsequently, other tuberous plants that they found in their American colonies were given the same name. Potata and potato are clearly cognate forms of batata, consequently, the word papa, which is still in vogue in whole of  the Spanish Latin America, never spread outside this area, even though the plant itself is now grown in most parts of the world. We can say with some certainty that the historical evidence clearly corroborates archaeological evidence about the origin of the cultivated potato from the Andes of South America.

EVOLUTION

The wild potatoes occur only in the Americas. They seem to have evolved by means of geographical and ecological isolation rather than by genetic incompatibility. The picture regarding the evolutionary relationships of various species is not very clear. However, the cultivated species were at one time confined to the Andes of South America and the lowlands of southern Chile, in both cases being adapted to the cool temperate climates of these regions. The related wild species are much more widespread. There are seven cultivated tuber bearing Solanum species, vie. S. stenotomum, S. ajanhuiri, S. phureja, S. chaucha, S. juzepezukii. S. tuberosum ssp. andigena, S. tuberosum ssp. tuberosum and S. curtilobum, occurring in a polyploid series with a basic chromosome number of 12 and ranging from diploid to pentaploid. Several of them are fairly similar to each other and for that reason were classified by Dodds as ‘groups’ of S. tuberosum rather than distinct species. Their probable evolutionary relationships are shown in Fig. 1.

The diploid species, S. Stenotomum is grown from central Peru to central Bolivia and is believed to be the most primitive, probably having been derived from the diploid wild species, S. leptophyes, or possibly S. canasense, both of which still occur in the central part of its distribution area. At least four wild potato species are widely believed to be involved in the process of evolution.  Evidence indicates that hybridization of S. stenotomum with the weedy species S. sparsipilum and subsequent chromo-some doubling produced the tetraploid S. tuberosum subsp. andigena in the central Andes. Some workers, however, consider that the tetraploid Andean potatoes are derived from S. stenotomum by simple chromosome doubling. This tetraploid sub-species was carried by ancient people into southern Chile, where it became adapted to the long day length, to evolve into subsp. tuberosum. A similar process in Europe caused the same development to take place under the long day conditions. However, it may also be stated that certain authors believe that subsp. tuberosum from Chile and Europe differ from subsp. andigena by certain cytoplasmic factors that it may have acquired from some wild diploid species, such as S. chacoense.

In pre-conquest days, the cultivated diploid species S. phureja evolved from S. stenotomum through a process of artificial selection by Andean farmers in lower, warmer eastern valleys and acquired shorter dormancy so that three crops could be grown in a year.

In contrast, natural hybridization of 5. stenotomum with the wild frost-resistant species S. megistacrolobum gave rise to the diploid S. ajanhuiri. The F hybrid produced the ‘Yari’ group of varieties and a probable back cross to the cultivated parent gave rise to the ‘Ajawiri’ group of varieties. Similarly the F cross from a series of hybridizations between S. stenotomum and the wild tetraploid species S. acaule gave rise to a highly sterile triploid S. juzepczukii, which incorporated the strong frost resistance of  S. acaule. A further natural cross between S. juzepczukii and S. tuberosum subsp. andigena produced the only slightly less frost-resistant pentaploid species S. curtilobum. This evidently involved a 2n gamete from S. juzepczukii and a normal gamete from S. tuberosum subsp. andigena. A series of crosses between S. stenotomum and subsp. andigena have given rise to the triploid hybrids named S. chaucha.

We thus have a network of cultivated species or species groups, which evolved chiefly in the central Andes of Peru and Bolivia, involving four original wild species, viz. S. acaule. S. sparsipilum, S. leptophyes and S. megistacrolobum. All but two of these cultivated potatoes have always been confined to that central area. However, the diploid S. phureja has extended northwards into Ecuador, Colombia and Venezuela, whilst the tetraploid S. tuberosum spread into southern Chile.

HISTORY

Early history

In South America, potato was the most productive source of main food for centuries for the people in the high Andes and southern Chile. Potatoes were dried by Andean Indians to make chuno for use during food shortage between successive crops caused by frost or other unfavourable growing conditions. Chuno is a freeze dried potato powder of the bitter, frost resistant potatoes grown at 3,600 to 4,400 masl. The process requires a dry climate with high day and very low night temperatures allowing freeze drying of potatoes for  several  nights followed by thorough washing for many days in running water. The long lasting chuno is finally prepared by thorough trampling of such potatoes by men and women folks to sqeeze water out of them and finally dehydrating them in hot sunny days and freezing nights for many days. Still an important food in the highlands of Peru, chuno has been aptly extolled for its virtues in an ancient Incan adage, “Stew without chuno is like life without love”.

The Spanish conquerors found potato being very widely cultivated in what are now Colombia, Ecuador, Peru and Bolivia and the Araucanian region of Chile. Following the conquest of Peru, the Spaniards introduced potatoes in Spain and further spread it to many European countries including Italy, Belgium, Germany, France, Switzerland, and Holland by the end of the 16th century. Initially, potato was grown only as a curiosity in the Europe’s botanical gardens and remained a shunned plant-at best food for swine and country bumpkins2 for next two centuries. It bore the wrath for causing war and lust to tuberculosis, rickets, syphilis and obesity.  Often it fell victim to its lineage being member of Solanaceae and having hallucinogenic and narcotic cousins as mandrake and deadly nightshade (Atropa belladonna) containing scopolamine and atropine like poisonous alkaloids used in ointments said to give witches the power to fly. Potatoes were banned being unworthy of  human consumption by the Scottish clergymen as they were not mentioned in the Bible. Possibly the word “spud” (present day English nickname of potato) got its name being acronym for the Society for the Prevention of an Unwholesome Diet, a 19th century activist group dedicated to keeping the potato out of Britain. The first edition of the Encyclopedia Britannica referred to the potato as a “demoralizing esculent”, esculent being an ostentatious word for food. Russians referred it as “Devil’s apples”, while in  France potatoes were thought to be fit only for animals and poor people. The potato’s struggle for acceptance in Europe took place at every level, from King’s kitchens to slum street corners, from the hallowed halls of parliaments to the battlefields of Seven Years’ War. Resistance to eating potatoes was so strong in parts of the continent that willing rulers virtually had to force potatoes down their subjects’ throats. In 1651, Frederick William of  Prussia even issued an edict to cut off the nose and ears of any one refusing to plant potatoes. Frederick the Great, still facing resistance more than a century later, sent a wagonload of tubers to peasants in a famine-stricken area, only to receive a petulant reply. The things have neither smell nor taste, nor even the dogs will eat them, so what use they are to us?’ forcing, the great leader to hold an open-air banquet where potatoes were served to prove that they are not only edible, but also fit for royalty. French potato enthusiast Antoine Auguste Parmentier even had to trick peasants into stealing tubers from Louis XVI’s Royal Gardens to convince them of the potato’s virtues.

The crop remained a botanical curiosity till about the mid-18th century, and was not grown in any western European country except Ireland, where potatoes became the most profitable new crop, mainly for human consumption, and for pigs thriving well on potatoes. In Ireland, the situation was very different where in the 16th century religious differences were cause for the feuds and unrest between the Norman-Irish aristocracy and the English people. The common people, depending and devoted to peaceful agriculture for livelihood, were the chief sufferers when their cattle were driven off or slaughtered by one side or the other and their land and crops ravaged either by the Irish or English. During these years the miserable peasantry on the brink of starvation was driven to rely more and more on the potato as source of food. However, when cattle, food stores, and standing crops were used or destroyed, potatoes being underground escaped destruction. People realized this and did not harvest and store potatoes, but dug them up as and when required with sufficiently leftover to serve as “seed” for the next crop. Thus the potato became the “chief food” of the people. In 1780, Young recorded that a barrel of potatoes containing 127 kg would last an Irish family of six persons for 6 days indicating on an average consumption of over 3.5 kg per person per day.

Throughout the 18'h century, none seems to have been aware of the danger to the economy of a nation dependent on a single crop. The warnings of Wakefield and by Curwen went unheeded till August 1845, when suddenly one warm, rainy day in August, an unknown malady (late blight) struck the Irish potato fields.

Potatoes quickly rotted in the fields, sending an unbearable stench across the countryside and repeating the same scene across whole of  Europe. This was also true in 1846, 1847 and 1848 resulting in famous famine and death of nearly 2.5 million and migration of one million Irish including the famous Kennedys and Reagans to North America.

One of the wars during the Hundred Years War in Europe was christened “Kartoffel Krieg”, or the potato war between the Prussians and the Austrians acquiring its name when the contending armies ate up all the potatoes along the battle lines in Bohemia and then called off the fighting.

Bacterial Diseases of Potato and their Management

The potato crop is prone to many diseases caused by pathogenic fungi, viruses, mycoplasmas and bacteria. Bacterial diseases reported on potato are: 1) bacterial wilt, Ralstonia solanacearum 2) soft rot of stem and tuber, 3) common scab, 4) pink eye and 5) ring rot sepedonicus Devis et al.  In India ring rot and pink eye do not occur. The leaf spot is a minor disease. Therefore, the following chapter pertains to only two economically important bacterial diseases, i.e. bacterial wilt and soft rot.

BACTERIAL WILT/BROWN ROT

Bacterial wilt/brown rot is the most destructive bacterial disease of potato. Besides potato, the pathogen Ralstonia solanacearum (formerly Pseudomonas solanacearum and more recently, Burkholderia solanacearum) also causes lethal vascular wilt diseases in more than 200 plant species belonging to at least 50 different plant families including several crops like potato, tomato, chilli, brinjal, pepper, ginger and others. In India alone more than 130 plant species belonging to 47 genera have been reported to be infected by this pathogen. It is the first bacterial disease recorded in India from Pune district of Maharashtra in 1892. In different countries it is known by different local names such as bacterial wilt, brown rot, Granville wilt, ring disease, slime disease, southern bacterial wilt. etc. In India it is widely known as ghera and uktha, bangle blight, bangdi or paryya. The disease has a history of changing cropping pattern in some parts of the world. Potato cultivation was abandoned in Ranchi district of Bihar due to severe bacterial wilt infestation forcing the farmers to shift to the cultivation of other crops. The disease is unpredictable as evidenced by recent outbreaks of bacterial wilt of potato in Europe. Resistance against bacterial wilt in potato is scarce and thermo-sensitive in nature. Therefore, it is apprehended that the disease might become more problematic, particularly in the event of changes in cultivated varieties and global warming.

Distribution

The disease is wide spread in tropical, sub-tropical and warm temperate regions and has been reported from six of the seven continents. It is endemic in South Asian, East Asian, Southeast Asian, and even in some central Asian countries. It is widely distributed throughout the Indian sub-continent including India, Pakistan, Nepal, and Bangladesh. In India R. solanacearum is prevalent in all the states excluding Punjab, Haryana, western part of Uttar Pradesh and Andhra Pradesh. The wide distribution of this pathogen is a reflection of its evolutionary success, which is correlated with the extent of genetic diversity within a species. In fact, the bacterium is notorious for its phenotypic diversity in respect to colony morphology, races and biovars, disease symptoms and host range. Modern techniques of molecular genetic analysis suggest that this bacterium probably originated from a common ancestor, possibly at a single location near the equator. Further evolution of the bacterium then occurred with several wild hosts, possibly in forest eco-systems in geographically isolated areas, creating plenty of diversity within this species.

Wilt incidence and economic losses vary from place to place, season to season and the stage of crop damaged. Crop loss up to a maximum of 75% has been reported in potato from India.

Etiology

The etiology of the disease was first established by Erwin Frink Smith in 1896 and the bacterial entity was christened as Bacillus solanacearum nov. sp. and later as Pseudomonas solanacearum. The bacterium belongs to beta subclass of the Proteobacteria. With the introduction of molecular techniques, generic nomenclature of the wilt pathogen underwent rapid change from Pseudomonas to Burkholdena to Ralstonia. Yabuuchi et al. 1992 proposed the new genus Burkholderia to accommodate RNA homology group II, including Pseudomonas solanacearum with P. cepacia as type species. Later work based on 16S rRNA genes and polyphasic taxonomy showed dichotomy in genus Burkholderia hence a new genus Ralstonia was proposed with R. picketti as type species.

R. solanacearum is a Gram negative rod measuring approximately 0.5-0.7 x 1.5-2.5 mm. Virulent isolates are mainly non-flagellated, non-motile and are surrounded by extracellular slime. Avirulent isolates are devoid of any extracellular slime, usually bear 1-4 polar flagella and are highly motile. Polar fimbrae are present which are associated with twitching motility and spreading growth on solid media. Cells contain inclusion of poly (b-hydroxybutyrate which are sudanophilic and refractile under phase microscope and commonly show bipolar staining. It is a chemoorganotroph with aerobic respiratory metabolism; catalase and Kovac’s oxidase positive; the optimum temperature for growth varies from 27-37°C depending on the strain, and nitrate is reduced to nitrite. R. solanacearum usually shows low level of salt tolerance, growth is often inhibited by 0.5 to 1.7% NaCI. The bacterium lacks fluorescence, phenazine and carotenoid pigments. A brown to black diffusive pigment is often produced on variety of agar media containing tyrosine.

Studies on host range, physiology, serology, membrane protein pattern, numerical taxonomy and bacteriophage susceptibility of the bacterium established highly hetero-geneous composition of this species. However, from a pathologist’s point of view R. solanacearum has been delineated into five races on the basis of host range (Table 1), and five biovars on the basis of ability to use disaccharides and hexose alcohols (Table 2).  Recent studies established existence of two broad RFLP divisions having only 13.5 percent similarity. In future, creation of more RFLP groups can not be ruled out. Marked differences in geographical distribution of races and biovars is observed. Race I/biovar III and IV is most predominant in Asia. Race 3 biovar II is restricted to cooler region of the world including tropical highlands.

Table 1.

Diagnostics and detection

The disease can be best diagnosed by observing symptoms. Expression of the disease may start as partial collapse of foliage followed by recovery and subsequent complete death (Fig. 1). Tubers largely do not show any external symptoms but Figure 1. Potato plant showing bacterial wilt symptoms transversely cut tubers from wilted plants show vascular browning and in exceptional cases tubers might ooze out slimy depositions  at eyes (Fig 2). Water soaked lesions on tubers lenticels have also been reported. Incipient infection of tubers Figure 2. Infected tuber showing bacterial ooze in vascular bundlecan be accentuated by incubating them at 30°C for six weeks and then tested for exudation of bacterial ooze in the tuber eyes. This test is advocated by the International Potato Center (CIP), Lima, Peru. Potassium hydroxide (KOH) test is useful to differentiate R. solanacearum infection from C. michiganensis ssp. sepedonicus. Precise diagnosis may be sufficient to take up suitable remedial steps. However, in many cases it needs to be followed by sensitive detection. Detection of the pathogen can be undertaken based upon the purpose, need, time, and the cost. This involves isolation and culturing on SMSA medium followed by metabolic profiling (Biolog system) and proving the Koch’s postulates (host test), using serodiagnostics (ELISA, Immunofluorescence) and confirming through molecular methods (PCR, Nucleic Acid Hybridization). Isolation of the pathogen in pure form can be avoided by adopting molecular detection techniques. Each of the above detection techniques has specific advantages and disadvantages in respect of specificity, sensitivity, time and cost. Each technique has a threshold level of bacterial population that can be detected

(Table 3).

Table 3. Sensitivity of the different techniques used for detection of R. solanacearum from potato Method Detection level Remarks (cells/ml)

Post Harvest Handling of Potato

1. SIGNIFICANCE

The unawareness about post harvest handling practices accounts for about 10-15% wastage of tubers. Nearly 10 per cent of the total production is used as seed tubers. There is a large gap between the existing storage facilities and the actual requirement thereof in the country. At present the cold storage capacity in the country is about 10.3 million tonnes, whereas the production of tubers is around 18 million tonnes. The post harvest losses can be minimised by generating appropriate techniques of tuber handling and storage. Public agencies and research organizations are engaged in reducing some of the problems associated with post harvest handling of potatoes.

Potato production in India has been increasing steadily during the last fifty years and the total production was 18 million tonnes in 1997-98. During the years of over production, we are unable to store or utilize the surplus potatoes available in the country. Consequently, we witness gluts at regular intervals, which means economic loss to the grower and wastage of precious food. Realising the importance of storage and processing for better post harvest management of potatoes, attempts were made at CPRI to study and understand the problems of potato storage during the hot, humid summer months and the problems related to potato processing in India.

Post harvest improvement such as fast and cheap transportation, storage and processing will help to make potato production more profitable for farmers by improving their access to markets, raising local value addition, and promoting greater competition among middlemen. The perishable nature of potatoes combined with the inadequate and expensive refrigerated storage facilities and their uneven distribution, difficulties in transportation, the adverse environmental conditions prevailing during the main storage and lack of significant processing of potatoes create market gluts around harvest time.

2. POST HARVEST LOSSES

The proper techniques during post harvest handling and storage should be used so that the losses due to physical causes like damage during digging, transport to storage etc. and physico-chemical changes like conversion of starch into reducing sugars, shrinkage and weight loss due to transpiration and respiration, rotting of tubers due to infection by micro organism etc. could be minimized. Post harvest losses result partly from insect damage and physical injuries like cutting by spades during harvest. Khatana et al. reported 6% wastage in the field, however wastage may vary from 2-25% depending on the weather which governs insect infection.

Physiological disorders like black heart and low tempera-ture injury are also a result of mal-storage practices. It renders tubers inconsumable thus causing great loss to grower.

3. ENHANCEMENT OF SHELF-LIFE OF POTATO TUBER

1. Avoid Mechanical Tuber Damage Including Internal Bruising

The damage can be controlled by reducing external forces imposed on the tubers during lifting and at various stages of handling by proper design and use of mechanical lifting and handling techniques. When the potato tubers get matured they are removed by digging with the help of spade or kudali due to which bruising is caused and skin is damaged. Splitting of tubers can be avoided by taking care during these operations. In prolonged storage internal bruising is caused by the pressure spots developed inside the tubers. The drizzling of rains, on hills during digging make the harvested tubers more susceptible to rot by organisms like Pythium, Phytopthora and Erwinia species. In the plains, late digging of potato, where temperature rises 25°C, the injury get prone to cause bacterial soft rot and charcoal rot (Macrophomina phaseolina).

2. Sorting and Grading of Tubers

Sorting is necessary to remove diseased and damaged tubers. The storability is inversely related to size of the tubers, so grading is essential. The tubers weighing more than 75g may be graded in to table purpose category. However, the small size tubers about 13-31 mm diameter are preferred for seed purposes which can economically be kept under country storage. Seed tubers below 25 mm size are categorized as under size and more than 65 mm as over size. Suitability for processing of potato tubers is decided according to its shape, size and depth of eyes and chemical constituents like tuber dry matter and reducing sugar content. Round to round oval potatoes are used for the preparation of chips while small sized tubers are used for canning, large grade tubers (40-60 mm. diameter) are preferred for chipping and for preparation of French fries.

3. Wound Healing and Curing

Wound healing in potato tubers has an important bearing on storage losses. Potatoes have relatively tender skin at harvest and some damage occurs invariably, wounds, if not properly healed soon after harvest, can result in excessive shrinkage and rotting during storage. Wound healing involves deposition of suberin. Wound healing is faster at higher storage temperatures. The process is slowed down at low temperature, increased CO2 concentration or by sprouts inhibitors used at the time of storage. Wound heating at 18°C is faster and it takes about 15 days whereas about 30 days are required at 12°C and at 10°C it is almost nil. For the formation of wound periderm, initially the cells at the cut surface become suberized followed by the development of meristematic layer called phallogen or cork cambium a few layers below the cut surface. The cut off layers towards the out side by division in the phallogen become suberized cork cells making the periderm a barrier for evapouration to water and entry of micro-organism.

For proper wound healing and curing potatoes after harvest are quickly dried, kept outdoors in heaps in the field or under the shade of trees or in sheds, undisturbed for some time. Heaps are covered with straw to protect them against frost and rains. The heaps may be 1-1.5 m high and 3.35 m wide at the base. Period of 10-15 days is sufficient for proper curing.

Thomas observed the effect of temperature and gamma irradiation on wound healing in the variety Kufri Chandramukhi and concluded that the major cause for the bacterial soft rot in tubers when they are stored under high tropical ambient temperatures or when irradiated for sprout inhibition is the impairment of wound periderm formation.

4. Weight Loss

Weight loss consists of starch and moisture loss through evapouration. Harvested potato tubers are living organisms who breathe in oxygen and give out carbon dioxide, water and heat as waste products from the organic process. This process is at the expense of stored starch in potato. The higher the temperature of the potato, the greater the loss of starch and the potatoes age. Starch loss is responsible for 10% of the total weight loss of healthy potatoes after storage. Damaged potatoes age more rapidly and loss moisture. Stored potatoes lose weight mainly due to two physiological processes- transpiration and respiration which can be reduced by increasing the relative humidity and reducing the temperature of storage atmosphere, respectively. These losses are generally low as long as potatoes remain dormant. When dormancy is over, there is an increase in these losses due to sprout growth. Higher weight loss is caused under the non refrigerated storage.

Transpiration was found to be the major source of weight loss during storage (18-30°C, RH 80-90%) for a period of 4 months. Contribution of respiratory carbon loss to total weight loss was slight (3.96 - 6.07 %) Respiration rate measurement with infra red gas analyser showed higher rate of weight loss in sprouting tubers as compared to dormant one’s while Mehta and Kaul reported that there was no correlation between respiration rate and weight loss during storage up to 10 weeks.

5. Dormancy

When freshly harvested potato tubers are placed under environmental conditions favourable for sprout growth, sprouting does not normally occur. The time of onset of sprouting is determined by the length of the dormant period of the tubers. Long dormancy may be considered as an important component of good keeping quality. However, storage trials conducted at Patna showed that the long dormant variety Kufri Sindhuri suffered maximum rotting and therefore it is not necessary that a long dormant variety should have a good keeping quality. An association between short tuber dormancy and earliness has been reported by Kaul and Mehta. Since weight loss and rotting tend to be higher in sprouted than in unsprouted tubers, therefore, long dormancy may be considered as an important component of keeping quality.

6. Storage Temperature

The temperature of storage is an important factor that determines the break of dormancy and the onset of sprouting. Storage trials carried out at Patna on various types of storage structures in decreasing order of temperature. Ordinary kutcha store, a double walled insulated store (27-30°C). An underground cellar and a pre-cooling room of a cold store (16-18°C) indicated that high storage temperature tend to retard sprouting. In the case of loose stored potatoes, the difference in temperature between the potatoes at the bottom and the potatoes at the top must not exceed 0.8°C. Greater differences in temperature may give rise to condensation and germination in the potatoes at the top.

7. Treatment of Tubers Against Diseases and Insect

Potato tubers may carry various types of disease inoculums and nematodes. For disinfecting the tubers, the fungicides (bavistin and benlate etc.), antibiotics (Streptocycline, tetracycline etc.) and insecticides, which are safer, should be used. Nagaich and Upreti eradicated the leafroll and yellow diseases by keeping tubers in hot air at 40°C for two hours daily for 6 weeks. Chemicals like H2SO4 (1.75%) (Dutta and Thaplyal, 1978) and boric acid 10%  have been reported to be effective in control of black scurf and scabs. These diseases can also be controlled by treating seed tubers with organomercurial compounds.

8. Use of Growth Regulators Against Sprouting

Tubers are living entities as they respire. The respiration rate is influenced by temperature and O2/CO2 ratio. It regulates the process of sprouting. The respiration of potato causes breakdown of starch into simple sugars which supplies food material to buds during sprouting. Energy and simple sugars also encourage cell division of buds.

Growth regulators synthesised during respiration are involved in the process of sprouting. The relevance of GA, Auxin and ABA during sprouting has been reported by various workers. Hemberge reported that the extract from dormant potatoes inhibited the coleoptile and inhibition activities remained higher during bud dormancy in treated coleoptile and decreased prior to sprouting. The compound was named as P inhibitor by Bennet Clark and Kefford. Later on Abscissic acid which was recognised as active component of the beta complex inhibitors has been isolated from potato tubers and confirmed its involvement in inhibition of sprouts. The mode of action of endogenous GA, other growth promoters and Abscissic acid in regulation of sprouts is well established fact where GA activates the buds while ABA was found associated with dormancy of tubers. Finally, Burton confirmed the involvement of ABA. The level of endogenous GA3 increases during termination of dormancy however, various experiments have shown that not only ABA-GA mechanism is associated with regulation of dormancy, but other chemicals are also taking part in this phenomena.

9. Regulation of Sprouting in Stored Potato

Suppression of sprouting in the storage should be emphasized to maintain the tuber quality and to prolong the shelf life of ware tubers. The spray of various growth inhibitors like MENA, 2,4,5-T, Maleic hydrazide and CIPC etc. are useful for sprout suppression in storage.

10. Pre-Harvest Application for Sprout Suppression

Maleic hydrazide (MH) has been found effective as sprout suppressant for table potatoes. The foliar spray of MH at the rate of 3000 ppm (approx 2 lit a.i./ha) remains effective during storage.

Spraying of MH 2000 to 3000 ppm (2-3 g/lit of water) at 2-3 weeks before harvesting has been reported to be effective in controlling the sprouting in storage at CPRI, Shimla. At IARI, New Delhi, however it has been observed that the translocation of MH was not uniform to all the tubers and as a result only about 15% of the tubers, showed positive effect on sprout control. MH is the chemical sprout suppressant registered for use in India. Trials were carried out with a liquid formulation containing diethonalamine salt of MH at Jalandhar, Shillong, Patna and Ootakamund. One spray of 0.3% MH equivalent, 2-3 weeks before harvesting did not reduce the yield significantly and resulted in no significant changes in the contents of starch, reducing sugar’s or soluble proteins. The sprout growth was significantly suppressed by MH treatment. The content of MH residues in the tubers was within the permissible limits (30-60 ppm). Hence MH is a risk less sprout suppressant for ware potatoes.

Biotechnology for Production of Quality Planting Material

Biotechnological approaches are now routinely used to obtain pathogen-free planting material in potato. Meristem culture was perhaps the first biotechnological approach successfully employed to produce virus-free potato clones. The technique in combination with accurate and sensitive virus detection procedures has been highly successful over the years in elimination of major viruses from systemically infected potato clones. Methods have also been developed for mass multiplication of virus-free mericlones using micro propagation. Virus-free in vitro plantlets, thus produced are either planted directly in the field for raising commercial crop or used for the production of microtubers in the laboratory or minitubers in greenhouses. These techniques have been successfully integrated in potato seed production programmes in many countries.

MERISTEM CULTURE

Over 30 viruses and virus-like agents infect potato (Solanum tuberosum L.) plants. Potato viruses are systemic pathogens, and therefore, perpetuate through seed tubers. Thus, the losses caused by viral diseases are not only confined to the year when infection occurs, but continue as long as the diseased tubers are used as seed. While plants infected with bacteria and fungi respond to treatments with bactericidal and fungicidal compounds, there is no commercially available treatment to protect virus-infected plants. Being dependent on host for DNA replication and protein synthesis, selective interference of viral multiplication by chemical means without adversely affecting the plant nucleic acid and protein synthesis is almost impossible.

The term ‘meristem culture’ denotes in vitro culture of meristematic dome of actively dividing cells located at the extreme growing tip of the shoot, along with a portion of the subjacent tissue containing one or two leaf primordia (Fig. 1). This piece of tissue is about 0.1-0.3 mm in size. In the absence of chemical control of viral diseases, meristem culture is the only available method to eliminate viruses from systemically infected potato cultivars. This technique is based on the fact that in rapidly growing meristematic tips viruses are either absent or their concentration is very low. Despite the phenomenal success of meristem culture in elimination of plant viruses, it remains still unclear as to why the apical/axillary meristems contain a little or no virus? There are several hypotheses.

Virus particles spread through vascular system but the vascular system is not developed in meristematic region.

Chromosome replication during mitosis and high auxin content in the meristem may inhibit virus multiplication through interference with viral nucleic acid metabolism.

Existence of virus-inactivating systems with greater activity in the apical region than elsewhere.

However, these hypotheses have never been proved unequivocally.

Various factors, like size of the explant, meristem location and cultural factors largely affect the success of virus elimination by meristem culture. In general, larger the size of the meristem, better the chances of its survival in vitro, whereas smaller the size of the meristem, better the chances of its being virus-free. As the distribution of a virus within a plant is uneven, especially towards the shoots tips, meristem of varying sizes are used to regenerate virus-free plants depending on the genotype and virus strain under consideration. It is difficult to excise apical meristems from terminal buds, because they have more rudimentary leaves and leaf primordia than the axillary buds. There is, however, no difference between the apical (axillary meristems and in terms of survival or freedom from virus infection. Therefore, axillary meristems are preferred to apical meristems in many laboratories for virus elimination.

Although it is possible to eliminate viruses from potato plants following meristem culture alone, plant regeneration from meristems takes four to eight months, and sometimes depending on the nature of the virus, the percentage of virus-free plants obtained from regenerated meristems is low. As a result, meristem culture procedure is often combined with thermotherapy and/or chemotherapy to increase the likelihood of obtaining virus-free plants.

THERMOTHERAPY

Growing host plants at higher temperatures significantly reduces replication of many plant viruses by disrupting viral ssRNA and dsRNA synthesis. Higher temperatures (35-37°C) cause disruption in the production and/or activity of virus-encoded movement proteins (MPs) and coat proteins (CPs). MPs are involved in cell-to-cell movement of viruses through plamodesmata and plant vascular system, while CPs play a role in the reconstitution of virus particles from replicated viral nucleic acids. Therefore, thermotherapy of infected plants followed by meristem culture improves virus freedom even from relatively large-size meristems. Reduction in virus titer is higher, if the infected plants are exposed to elevated temperature for longer periods. Current virus elimination programmes involve either growing of whole plants or in vitro cultures at temperatures close to the threshold of normal plant growth. The exact temperature and length of treatment vary with the virus and the heat tolerance of the host plant.

Meristem culture combined with thermotherapy is widely used for virus elimination in potato. The source plants infected with viruses are incubated in a growth chamber under light intensity of 30-50m mol m s at 35-37°C for 2-6 weeks. After respective periods of thermotherapy. the meristems are excised and cultured on nutrient medium for regeneration.

Cold therapy followed by apical meristem culture has also been shown to successfully eliminate several viruses from infected plants. Viroids, some of which are quite resistant to elevated temperatures, have been effectively eliminated by cold therapy. Low temperature therapy (4-7°C) followed by meristem excision and regeneration has been used to eliminate potato spindle tuber viroid (PSTVd) from infected potato plants.

CHEMOTHERAPY

Chemotherapy involves the use of chemicals like antibiotics, plant growth regulators, amino acids, purine and pyrimidine analogues to inactivate viruses or inhibit replication/movement of viruses in tissues. These chemicals can either be sprayed on growing plants prior to excision of meristems or incorporated into tissue culture media. As early as in 1954, eradication of  PVX from potato tissue cultures by malachite green and thiouracil treatments was reported. Of all the chemicals tested for plant virus elimination, synthetic nucleotide analogues like ribavirin (Virazole: 1-D-ribofuranosyl-1, 2,4-triazole-3-3carboxamide) and DHT (5-dihydroazauracil) have been particularly effective in inhibiting different plant viruses. In vitro chemotherapy of meristematic explants with antiviral chemical ribavirin has been found to be most promising for elimination of major potato viruses. Though the exact mode of action of ribavirin on plant viruses is not understood, following possibilities have been suggested:

•          Ribavirin triphosphate, a major derivative of ribavirin, inhibits viral RNA polymerase synthesis.

•          Ribavirin-5-phosphate, a derivative of ribavirin, inhibits IMP-dehydrogenase, and thereby decreases the GTP pool and nucleic acid synthesis.

•          Ribavirin interferes with capping at the 5' end of viral mRNA leading to inefficient translation.

Other antiviral chemicals such as 8-azaguanine, 5-fluorouracil, 2-thiouracil and Para-fluorophenylalanine have also been tested for virus elimination in potato. The concentrations of many antiviral chemicals required during chemotherapy to inhibit virus multiplication are very close to the toxic concentration for the host plant. In addition, there is always a possibility of mutations when the plants are exposed to antiviral chemical. Therefore in vitro ribavirin therapy at low concentrations combined with thermo therapy has been used to eradicate viruses from infected potato cultivars. In such cases simply culturing the shoot cuttings can eliminate some viruses like PVY/A and PLRV in potato.

ELECTROTHERAPY

Electrotherapy of explants of infected potato plants has recently been reported to be an effective means for virus elimination. Potato stems infected with PVX were exposed to 5, 10 or 15 mA for 5-10 minutes followed by immediate culturing of the shoot tips in vitro. The highest efficiency was obtained at 15 mA for 5 min, and about 60-100% of the regenerated plantlets tested negative against PVX. Electrotherapy technique is yet to be tested against other potato viruses.

VIRUS DETECTION AND DIAGNOSIS

Even after taking all precautions to excise small meristem tips and subjecting them to various treatments favouring virus elimination, ultimately very few virus-free mericlones are obtained. Therefore, meristem-derived plants must be tested for virus freedom before using them as mother plants in micro propagation. Accurate, sensitive and rapid detection of potato viruses is critical for identifying virus-free mother plants and their integration into seed production programme. A wide array of serological and nucleic acid-based assays are available for accurate detection and diagnosis of potato viruses.

Enzyme-linked immunosorbent assay (ELISA), dot immunobinding assay (DIBA) and immunosorbent electron microscopy (ISEM) are most widely used methods for detection of plant viruses. Serological assays involve trapping virus particles on a supporting surface to which a specific antiserum has been attached. An ELISA in a microtitre plate or dot blots on a nitrocellulose membrane are used to produce a colour reaction dependent on the virus concentration. In ISEM, the trapped and negatively stained viruses are viewed under the electron microscope. ISEM is used when an available antiserum contains non-specific antigens that reduce ELISA specificity. Protein-A complemented immune electron microscopy (PAC-IEM), a modification of ISEM. makes use of protein-A’s high affinity for IgG to enhance trapping and minimize non-specific trapping of virus particles. Over the years various modifications have been introduced in ELISA systems with increasing availability of monoclonal and polyclonal antibodies to reduce host antigen background reactions.

Nucleic acid hybridization is based on specific pairing between the single standard DNA or RNA and a complementary nucleic acid probe to form double stranded nucleic acid. Thus, either DNA or RNA sequences may be used as probes for detection of plant viruses. Hybridizations are usually carried out on solid support (nitrocellulose or charged nylon) where the target nucleic acids are immobilized and the labelled nucleic acid probe is allowed to hybridize to them. RNA probes specific for Potato spindle tuber viroid (PSTVd) have been synthesized from a full length PSTVd cDNA. and used successfully for PSTVd detection in potato. Improvements in hybridization assays have been made in recent years using non-radioactive detection systems. Nucleic acid probes can be labelled by incorporation of biotin-11-UTP or digoxigenin tagged DTP, and can be detected by streptavidin or anti-digoxigenin antibody-enzyme conjugate, respectively. Biotin-labelled probes have been reported for PVS, PVX and PSTVd. Polymerase chain reaction (PCR) combined with reverse transcription (RT-PCR) has also been used for detecting picogram quantities of viral nucleic acid in infected tissues. With its relative simplicity and high sensitivity, the PCR-based methods will be increasingly used in future to detect and diagnose plant viruses.

MICROPROPAGATION

Micro propagation allows large-scale multiplication of virus-free potato micro plants. Nodal segments of virus-free potato microplants are cultured on semisolid or liquid medium under aseptic conditions for obtaining new microplants. Murashige and Skoog’s (MS) medium supplemented with 2.0 mgl D-calcium pantothenate, 0.1 mgl GA 0.01 mgl NAA and 30-gl sucrose is best suited for propagation of potato microplants in vitro. Cultures are usually incubated under a 16-h photoperiod (50-60m  mol m s light intensity) at 24 °C. Usually, three nodal cuttings (1.0-1.5 cm) are inoculated per culture tube (25x 150 mm), and the tubes are closed with cotton plugs. Within 3 weeks the axillary/apical buds of these cuttings grow into full plants. These plants can be further sub-cultured on fresh medium. At an interval of every 25 days of sub-culturing, theoretically 3 (14.3 million) microplants can be obtained from a single virus-free microplant in a year.

Virus-free micro-plants can be used for direct transplanting after hardening, in the fields or nursery beds for production of normal tubers or minitubers, respectively. Alternatively these plants can also be used for the production of microtubers in the laboratory. Microtubers are miniature tubers produced under tuber inducing conditions in vitro. These small dormant tubers are particularly convenient for handling, storage and distribution. Many protocols have been developed for induction of microtubers in vitro. Most of the published work on potato microtuberization is focused on the use of cytokinins, especially N-benzyladenine (BA). Other substances like abscisic acid, chlorocholine chloride (CCC), NAA, triazoles, coumarine, acetic acid and jasmonic acid have also been used for induction of microtubers in potato. MS basal nutrient mixtures are universally used for potato microtuberization. Sucrose is the most effective carbon source, and an increase in its concentration to 8% induces early tuberization, whereas concentrations above 8% are inhibitory.

Temperature and photoperiod are two important physical factors that affect potato microtuber induction in vitro. The optimum temperature for in vitro tuberization is 20°C with a constant temperature being more effective than alternating day-night temperatures. Temperatures below 12°C and above 28°C have been found to be inhibitory to potato microtuber production. In general, optimum microtuberization occurs under continuous darkness during cytokinin-induced tuberization, but a longer photoperiod with higher light intensity is required when cytokinin is not used.

At Central Potato Research Institute (Shimla) microtubers are induced in MS medium supplemented with 10 mgl BA plus 80 gl sucrose, and the cultures are incubated under complete darkness at 20°C. Microtubers begin to develop epigeally 1-2 weeks after incubation depending on the genotype, and are harvested after 60-75 days of incubation. In general, 15-20 microtubers with an average weight of about 100-150 mg can be obtained from each flask/magenta box. Before harvesting, the magenta boxes are shifted under diffused or artificial light at 20-24°C for 10-15 days for greening the microtubers. Thereafter, green microtubers are treated with 0.2% Bavistin, dried at 20°C, packed in perforated polythene bags, and stored under dark at 5-6°C till dormancy release. These microtubers are planted on nursery beds under aphid-proof net houses (50 microtubers/m2) in seed producing areas of the Indian plains. The microtuber crop is allowed to mature in the nursery beds to produce minitubers.

True Potato Seed Technology

Potato, unlike other solanaceous crops such as tomato, brinjal, chilli, capsicum, etc. is traditionally grown vegetatively by planting tubers called seed tubers. Because of ease in planting tubers and other cultural operations, the vegetative or asexual mode of propagation became the standard cultivation practice soon after the ancient farmers domesticated the potato as a food crop. Nearly 2.5-3.0 tons of seed tubers are needed to plant a hectare of potato crop. Seed tubers are bulky containing nearly 80% water that makes their transportation from one place to another difficult and expensive. They, however, degenerate due to infiltration and accumulation of viruses when the same seed stocks are repeatedly used over the years resulting in serious yield losses. This necessitates replacement of old or diseased seed with fresh healthy seed. The production of healthy seed tubers is expensive and the low rate of tuber multiplication (normally 6-8 times) provides only a limited quantity of quality tuber seed. Further, the low aphid areas suitable for producing healthy seed in the country lie in northern plains or higher hills and transportation of seed tubers to distant areas for producing table potatoes adds to the cost of seed and cropping. Therefore, the high cost and inadequate availability of healthy tuber seed are most binding constraints in the production and productivity of potato in the country. To overcome this, an alternate technology of true potato seed (TPS) or use of botanical seed for commercial potato production has shown great promise for producing both disease-free and cheaper seed and thereby, reducing the cost of cultivation.

ROLE OF TPS POPULATIONS

TPS is a sexually reproduced propagule in potato and results from the fertilization of ovules, which develop into tiny seeds inside the fruit called berry. The seed thus produced is called TPS or botanical seed to distinguish it from the conventional tuber seed. True seeds have the potential to develop into full-grown plants and produce tubers.

Potential and advantages of TPS technology

TPS has an edge over tuber seed for various attributes of potato production (Table 1) Thus, it can effectively overcome some of the problems associated with seed tubers and can be used easily by the resource poor farmers to produce healthy planting material in any quantity as and when required. It offers many advantages to the farmers to overcome weaknesses of clonally propagated tuber seeds.

Source of healthy planting material: Except potato virus T (PVT) and potato spindle tuber viroid (PSTVd) no other major pathogen is transmitted through TPS as they are filtered out during pollination and fertilization.

Saving seed tubers for consumption: Nearly 18% of the total tuber produce retained as seed can be used for consumption.

Low cost of cultivation: Cost of planting material produced through TPS is approximately one-tenth of the cost of quality seed tubers.

Easy storage: TPS with 3-5% seed moisture can be stored for many years under ambient conditions in dark with practically no loss in germinability atleast up to 5 years.

Easy and inexpensive transportation: Only 100g of TPS can replace 2-3 tonnes of seed tubers required for planting one-hectare land.

Potato cultivation in non-traditional areas: TPS can be used for potato cultivation in areas deemed unfit for producing quality seed tuber due to unfavourable agro-climate.

Fitness of potato in different cropping systems: TPS can be used to fit potato in different cropping systems when tuber seed of correct physiological age is not available as and when required for planting the crop.

Environment/user friendly: The pathogens unlike in clonally propagated crop are unable to affect the TPS crop due to in-built resistance (multi-line effect) for diseases/pests. Consequently, less amount of pesticides is needed for spraying TPS crop. Thus TPS is not only cost effective but also environment friendly.

Constraints/shortcomings in the adoption of TPS technology

TPS presents following disadvantages, which have been the major bottlenecks in adoption of TPS technology.

TPS produced crop takes about 15-20 days more for maturity compared to that from seed tubers.

Potato seedlings are vulnerable to environmental stress and damage due to insect/ pests and need more care/labour input especially during the initial phases of growth and establishment in transplanted crop.

Crop from TPS populations are less uniform in plant type/maturity, tuber shape, size and dry matter.

Further, true potato seed has a dormancy of about 6 months. Low-quality and dormant TPS usually does not germinate uniformly and produces slow-growing seedlings that are highly vulnerable to transplanting shock. Thus, plant maturity is extended and production of large tubers is delayed or small tubers are produced due to the usually short growing seasons in tropical areas. When high-quality and non-dormant TPS is sown, the seedlings are uniformly ready for transplanting in only 3 weeks, instead of 6 weeks. Seedlings from non-dormant TPS, unlike those from dormant ones, are able to withstand bare-root transplanting shock and grow vigorously soon after transplanting and to a size similar to those of plants grown from seed tubers.

Early history

South American farmers have been using TPS to revive their potato stocks from time to time. However, the idea of exploiting TPS for commercial production of potato was conceived as early as 1949 in India when Dr. S. Ramanujam, founder Director of Central Potato Research Institute (CPRI), carried out field trials on utilizing TPS for ware potato production. The self-pollinated seeds of cultivar Thulwa’, which flowered under natural short pholoperiods during winter season in the eastern plains, were used for growing the commercial crop. Seedlings from self-seeds of Phulwa showed high degree of heterogeneity for most of the traits and resulted in poor yields due to inbreeding depression. This did not encourage the earlier efforts of growing a commercial potato crop from TPS. The programme of raising crop from true seed was resumed in late seventies after CIP was established in 1973. They identified TPS technology as one of their thrust area for the third world countries. The work was started in India at the Central Potato Research Institute, Shimla, and at International Potato Center (SWA Region). New Delhi. The efforts for reducing the problem of segregation in the progenies by developing inbred lines were given up. Instead, the early efforts concentrated on evaluation of open pollinated and hybrid populations developed through bi-parental mating in tetraploid potato for identification of progenies with high productivity and low variability for maturity and tuber characters. Work was also taken up on standardization of agronomy of raising the crop through TPS. The studies were later extended to flowering behaviour, induction of flowering under short photoperiod, techniques of pollination, TPS characteristics, etc. Since 1985. The All India Coordinated Potato Improvement Project through its network of centres all over the country located in State Agricultural Universities (SAUs) has been involved in conducting trials mainly for evaluation of high yielding TPS populations.

Priority areas for TPS dissemination TPS technology has a wider scope for its adoption in areas where quality tuber seed of a variety can not be produced, yields are extremely low due to availability of poor quality seed, seed tuber storage and transportation are expensive, skilled labour is available and consumers do not have any preference for specific tuber characteristics. In the Indian perspective, TPS technology is suitable in the states of Maharashtra, Madhya Pradesh, Orissa, north-eastern hill states (in the first priority) where yields are extremely low (< 10t/ha) due to poor quality seed tubers. Gujarat. South Bihar and West Bengal (in the second priority) where seed tubers of desired health standard can not be produced and are procured regularly from northern part of the country.

Economics of TPS technology

The high cost of potato cultivation in conventional system is mainly due to higher prices and planting rate (2.5t/ha) of tuber seed. The cost of planting material from TPS is merely one-tenth the cost of tuber seed (Rs.25000-30000) for one hectare. Singh and Jee have shown higher net returns for seedling tubers (Rs. 19,552 ha) and seedling transplants (Rs. 19,174 ha) as compared to seed tubers (Rs. 11,566 ha) of a variety under Patna conditions. Another study also indicated higher net benefits (US$ 415/ha) from potato cultivation through seedling tubers than tuber seed due to reduced production costs and improved yields. Seedling tubers are planted at relatively lower rate (by weight) and are resistant to late blight than the existing varieties in the area. Thus the difference between the crops from TPS and traditional seed tubers primarily relate to lesser expenditure on planting material and use of pesticides in TPS raised crop compared to seed tuber crop. The price of seed tubers in India vary with the price of ware potatoes, increasing rapidly as cold-store stocks are exhausted.

Seed Production

SEED POTATOES

Healthy seed potato is an important input needed for harnessing technological benefits of potato cultivation. About 3.3 million tonnes of certified seed is required for the area existing under ware potato in the country 35 q/ha. When various types of seed is used (cut, under size and whole tubers) But if the whole tubers of 30-80 g are used then 4.6 million seed is required for seed and ware potato 35 q/ha for 1.3 million hectare area. To produce this quantity of seed about 2.0 to 2.8 lakh hectare area is needed annually. The major constraints in attaining potato productivity is disease free seed and its higher seed cost.

The first scheme for seed production in India was started in 1941 at Shimla by the Imperial (now) Agricultural Research Institute, New Delhi. Under the scheme, partially disease free seed of exotic varieties used to be produced by intensive roguing in the hills. Lateron, production of quality seed stocks of commercial varieties was taken up by mass selection. The selected apparenly healthy plants were multiplied at Kufri. Because of low aphid population in high hills of Himachal Pradesh, quality seed of potato used to be produced in these high hills. Which become the main source of quality seed for plains. Seed potato posed many problems. These were (1) it became obligatory to have varieties that could perform well under diverse agroclimatic conditions of both temperate and subtropical plains. (2) Dormancy of hill grown seed prevented immediate planting in the plains, (3) mild hill climates harboured many soil borne diseases and the hill grown seed was a potent source of many soil and tuber borne diseases, and (4) due to limitation of land in the hills, the seed produced in the hills was Inadequate to meet the requirement of entire country. To overcome these problems and to reduce the dependence of the country on hill grown seed, a survey was conducted to locate the aphid free zones in the country and it was found that seed potatoes could be successfully grown in many parts of the North and north central Indian plains under low or no aphid conditions, with certain minimum precautions. This led to the development of “Seed Plot Technique”.

With the development of “Seed Plot Technique” a Scientific Seed Potato Production Programme of breeder seed was initiated at the CPRI in 1967 in a phased manner. The breeder’s seed production method consists of selection of clones and indorsing of representative tubers (4 Nos) from each clone for their virus freedom some important points taken in to consideration as stated by Jr. Jan Morrenhof Virus free tubers by indexing and their field multiplications in stage 1 to 4  under strict supervision to protect the seed crop from degenerative diseases. Integration of meristem culture and micropropagation techniques in the initial stages of breeder’s seed production can improve the quality of breeders seed. The breeders seed is further multiplied in foundation and certified seed stage.

As a rule, seed tubers are used for planting. These tubers, basically do not differ from tubers that are used for consumption purposes. Sometimes farmers use part of their own harvest as planting material for the next season. However, in many places, farmers do not use their own produce, but purchase seed from reliable source every year or after a number of years. The reason is that not every potato is suitable to be used as seed and that not every area and every season is suitable for the production of seed. Further more, not every farmer, region or country possesses the skills and or the necessary equipments and infrastructure which are required for the production of good quality seed. The use of quality seed is not only the basis for high production and good quality but also of a sustainable production system. The difference between the use of seed potatoes of good or of inferior quality may express itself in yield differences of 20 to 50%.

Variety : Some varieties can be grown in many places and have a wide range of adaptability; others are meant for very specific purposes or for specific environmental conditions. Apart from production capacity, an important varietal characteristic is the resistance to pests and diseases. Varietal purity is an important requirement for quality seed lots. Admixtures of other varieties will result in varying requirements with respect to agricultural practices like fertilizer harvest time, etc., if rouged out before harvest. They will also affect the marketability and price.

Diseases : It is essential to know which diseases/pests are important under prevailing conditions and the level of risk they impose. It can then be decided whether more or less strictness is required, regarding their persistence in the seed. Relevant tolerance levels are established for each of them. In some cases, the tolerance will be zero, especially in the case of quarantine diseases, which are known to be seed and soil borne, and which are not generally’present in the country or in a certain area. The seed production system should be based on a proper pest risk analysis.

Degeneration : When a crop is infected with virus, its yield will be affected. The rate at which the yield reduction will take place depends on the intensity of the infection, the type of virus and the combination of other yield affecting factors that are present. A crop that is already under stress from other factors, will suffer more from the virus infection. In general, a low infection level will have little effect on the yield, but high infection levels can result in yield losses upto 50% or more in case of dangerous viruses like potato virus Y (PVY) or potato leaf roll virus (PLRV). If proper measures are not adopted to control the spread of the viruses, the infection level will increase progressively from one generation to next when the potatoes are produced. Gradually, or reduction in productivity of the crop is observed in successive generations. This process is called “degeneration”. The degeneration speed and severity is not the same every where, it depends on presence of vectors and sources of infection available. Degeneration rate in warm climate is higher.

In general, the production of the lower seed classes (later generations) is done in the field and follows the same principles every where in the world. Only the number of multiplications and the level of quality maintenance may differ. For the production of basic seed, however, there are some distinct approaches that can be followed. The conventional system is through clonal selection, which fully takes place in the field. Newly developed systems are the rapid multiplication techniques, using laboratories and green screen houses.

In the past, clonal selection was the only system available for the production of basic seed. Typically true-to-type and apparently healthy looking plants were selected to start the cycle. The progeny of one plant formed a clone. The clones were kept separate from the others during three to five years of multiplication.

Simultaneously, in the same year, several clones of several varieties were multiplied side by side, depending on the expectations of the future seed demand. During the whole process, the health and quality characteristics are strictly monitored and in case a single diseased, from the system. After two or three multiplications the individual clones of one variety were bulked and constituted as one lot. The thus produced pre-basic seed was (or has to be) absolutely true-to-type and free of all diseases. Presently, starting a multiplication cycle, absolutely true-to-type and disease free material must be obtained. This is done by growing a meristem culture of shoot tips of true-to-type and healthy plants under sterile conditions in a tissue culture laboratory. From the culture, small plant lets are raised invitro, which are kept in test tubes or small transparent plastic containers. These invitro plantlets can under aseptical conditions be cut into small pieces, each consisting of a piece of stem with one node, which are again placed in tubes or containers on a growing medium. From the bud, present in the node, small shoot will develop, which will develop into small, but complete plantlet. The procedure can be repeated as often as desired. It takes about one month between cuttings and each plantlet can be cut into 5 to 8 pieces. At a desired moment, the plantlets can be transplanted in green houses and allowed to grow into normal size plants, producing normal tubers. As the plantlets are vulnerable, they are normally passed through a hardening process in green or screen houses before entering the open field. Alternatively, they can be planted directly in the field under protective nets.

Instead of using plantlets in test tubes, nodal cuttings can also be taken from bigger plants. When laboratory space is limited, the in-vitro plantlets can be transferred from the tubes to pots in green houses. After some time, nodal cuttings can be made from the stems of these plants, which can be rooted in soil sand and FYM mixture (1:1:1) to be grown into normal plants (either or not via transplanting). With the new shoots, growing from the same mother plants, the process can be repeated two to three times. Then they are left to grow to maturity. Mini tubers are produced from in vitro plantlets after they have been planted at high density (100 plants per m_) in beds in green or screen houses. The plants remain small and consequently small tubers are produced. Mini tubers of 15-25 mm sizes are preferred. The mini tubers thus produced, can be planted directly in the field and enter the seed production chain. When compared to clonal selection, the mini tuber production requires high investment in laboratories and green house, which makes it more expensive. The advantage, however, is the fact that the tubers have been less exposed to infections with diseases than the clones that have already been in the field for a number of generations. This may be of particular importance in places where high degeneration rates prevail or a disease of serious nature occurs in the region.

SEED PLOT TECHNIQUE

Potato seed production on scientific lines in India has been started since 1966 through the technique, which is known as seed plot technique. The main aim of this technique is to exploit the vector (Aphid-Myzos persicae) free period in the Northern plains with adjustment of planting and lifting dates and by adoption of appropriate plant protection management and method of cultivation for disease free seed.

The cultural requirements of the crop grown for seed differ from ware potato production. Different practices followed in seed plot technique are discussed as under -

Selection and preparation of field : The potato crop should not be repeated in the same field. The planting of potato in chilli, brinjal tomato and okra crop rotation is not recommended so that the disease intensity would be lowered down. Adoption hot weather cultivation and 2-3 years crop rotation is recommended to avoid buildup of soil borne pathogens such as black scurf and common scab etc. Minimum isolation distance of 25 metres from the ware crop should be kept.

Field in which potato seed crop is to be grown should be deep ploughed during summer and left as such. This will help in controlling certain pest and diseases and also the weeds.

Seed : Seed should be healthy, essentially free from the viruses, soil borne diseases like bacterial wilt, common scab and nematodes etc. genetically pure and of uniform size. Genetical purity is of great importance in potato seed production programme. The identification of potato varieties at their sprouting stage can be possible. A reliable method has been developed using the sprout grown in the light. Another method employed now a days to draw sample from the seed stocks and plant them under long day conditions where flowering is obtained to determine whether the variety is true to the type or not. The minimum size of seed accepted is 28 to 35 mm and maximum size permitted for seed potatoes can be as large as 80 mm but often not more than 55 to 60 mm. Generally 15 stems per m_ should be there small tubers have less sprouts than bigger ones, but their weight is also lower. Morrenhof  reported that to around 15,00,000 obtain stem per hectare, 60,000 tubers, equivalent to 1500 kg are required when size of 28-35 is used, against 30,000 tubers equivalent to 2700 kg when the size 45-55 is planted under Netherland conditions.

Pre-sprouting of seed tubers before planting increase the number of stems per tuber and also hastens quick, uniform and full germination. The seed stock of early varieties should be withdrawn from cold storage atleast 7 days before planting and that of late varieties 15 days before planting. The number of sprouts from a seed tuber depends on a function of variety, physiological age of tuber and the temperature of the chamber in which the seed is kept for sprouting. An ideal temperature for sprouting is 10-12°C.

Thermotherapy : Several varieties have been completely cured of PLRV by heat treatment at 35°C, for 56 days and at 36°C for 39 days Thirumalchar demonstrated this in the stocks stored in improvised stores under warm conditions at Patna.

Planting

Seed size and spacing : Whole potato tubers of about 45-50 g are used for seed crop. Tuber number is a function of plant density, which depends on the number of main stems. Proper combination of seed size and spacing is therefore, essential to get the number of required stems per ha. About 30 main stems per m yield maximum seed sized tuber. For this, there must be 70,000-80,000 plants per ha. In India, with careful manipulation of sprouting, tuber size, spacing and time of planting, an average of 4.5 stem per plant can be achieved with seed tubers between 20-25 g when spaced at 50 x 20 cm, 50-100 g seed at 60 x 25 cm and 100 g and above at 60 x 30 or 60 x 40 cm. 10-20 g tubers at spacing of 40 x 15 cm seed produced maximum quantity of C grade tubers (>25 g in weight) which are suitable for planting.

Time of planting : In hills the planting time is mid April. It may differ because of temperature variation. In plain, the planting time ranges from first week of October to 1st week of November depending upon the region. The temperature should be ranged between 8 to 28°C during the crop season.

Fertilization : The fertilizer requirement will vary with soil and previous crop taken. In general about 120-150 kg N, 80-100 kg P2O5 and 100 kg K2O per ha may be used in seed crop. Heavy application of nitrogen may delay tuberization, masking of virus symptoms and delay in maturity.

Irrigation : A light irrigation should be given to the crop immediately after planting, if pre-planting irrigation is not given. Pre-planting irrigation assures the uniform emergence. Second irrigation should be given about one week after planting and subsequent as and when required.

Weed control: Full earthing up may be done at planting and pre emergence herbicides are used to control, the weeds and avoid spread of contagious viruses. Weed control through cultural method is generally not advised. Because the frequent entry of man and implements are likely to spread contact viruses like. PVX and PVS. For pre-emergence weed control, herbicides like Pendimethalin, Alachlor, Metribuzin etc. may be used.

Roguing and Inspection : Diseased and off type plants should be pulled out along with mother tuber and newly formed tubers if any as soon as they are identified. This practice should be repeated twice or thrice to avoid the varietal admixture and keep the crop free from viral and phytoplasmal diseases. Inspection of seed crops should be done 3 times at 50, 65 and 80 days during growing season and remove all off types and diseased plants showing symptoms of viruses should be removed.

Haulm cutting : Haulms destruction is a must to prevent the infection/ transmission of virus infection by aphid (Myzus persicae). The aphid population starts building up in the end of December or 1st weeks of January. At this stage haulms should be removed either manually or by using the chemicals. Paraquate Chloride @ 2.5 lit/ha is most effective for killing of haulms. Singh et al. After removing of haulms the field should be inspected periodically and regrowth if any, should be destroyed.

Aphid management : This is one of the most important practices of the Seed Plot Technique. The aphid population should be recorded periodically and when it reaches above the threshold 20 aphids per 100 compound leaves, dehaulming should be practiced. There should be at least 75 days low aphid period or aphid free period so that an economical yield could be obtained from early bulking varieties. In plains, the effective aphid free period is too short. The crop can be escaped from build up of aphids, if it is harvested early. In such areas, reasonably healthy seed with good yield can be produced with the management of aphid population below threshhold level with the use of systemic insecticides like. Phosphomidon, Monocrotophos, Dimethoate

etc. (100-125 ml in 100 litres of water). In case of early appearance of aphids spraying of crop should be done in first week of December.

Disease and Pest Management : The potato, is prone to number of diseases. The seed should be free from seed borne diseases and pest so that the crop is not economically affected in yield and quality. Viral diseases are particularly important in potato seed production programme. The control of fungal, bacterial, namatodal diseases also determine the value of the seeds potato. Use of granular insecticides such as Thimet 10 G (15 kg/ha) at the time of planting is essential in plains to control the aphids. Spray the crop with Endosulfan 1.5 lit/ha or corboryl 2.5 kg/ha is sprayed if leaf catterpillar damage is noticed. Ridges are treated with chloropyriphos 2.5 lit/ha to control the damage of cut worm. One spray of Rogor or Metasystoc in the first week of December will check the aphid and also other sucking type of pests. One or two protective sprays of Dithane-M-45 > 2.5 kg/ha against early and late blights are required. When epidemic of late blight is observed Ridomil Metalaxyl 2.5 kg/ha should be sprayed. Spraying should be done from 3rd week of November at 10 days interval.

Harvesting and storage : Harvesting should be done after 15-20 days of haulms cutting so that the skin of tubers gets hardened. Delay in harvest will spoil the quality due to high temperature in March-April in the plain’s. The harvested tubers should be kept in a cool place for about 15 days for curing. Seed tubers should be graded before transporting to the cold store. The small size tubers should be kept as seed tubers.

Seed treatment : After grading, the tubers are washed with 1% chlorocin solution followed by rinsing in water and dipping in 3% boric acid for 20 minutes. After treatment the tubers are dried in