Potato and Tuber Crops

Rapid Multiplication of Basic Seed

With the aim of reducing field multiplication stages from four in conventional system to 2 or 3 a number of rapid multiplication techniques have been developed for quick potato multiplication (Naik, 1985; Naik and Singh, 1988).

1. Using sprouts, single node cutting
2. Stem cutting
3. Minituber production
4. Micropropagation

1. Multiplication Using Sprouts
• This is a simple rapid multiplication technique and can yield between 40 and 100 plants from a single tuber in a period of 2-4 months if sprouts are repeatedly harvested from mother tuber.
• The multiplication potential can further be increased if the harvested sprouts are cut into pieces, each having one or two nodes.
• Indexed tuber is ideal for multiplication through sprouts because scooping of a apical eye during indexing breaks apical dominance, and can support (nutritionally) growth of number of sprouts emerging from well spaced eyes.
• Using this method, an average of 10 sprouts can be obtained from single indexed tuber (Sarjeet Singh and Naik, 1993).
• Average establishments of about 89 per cent for sprouts in polythene bags and 69 per cent for sprouting in the field can be obtained with the above technology.
2. Multiplication Using Single Node Cutting (SNC)
• The method has tremendous multiplication potential under ideal environment.
• Young plants with 5-6 simple leaves can be obtained from sprouts, test tube plantlets, microtubers or minitubers.
• The stems are cut leaving 1-2 leaves at the base to get regrowth from axillary buds. The cut shoot is then further cut into pieces, each having a node with a leaf.
• Such cuttings are planted in sand beds for rooting and growth of axillary buds.
• Successive stem harvests can be taken from these mother plants in similar manner at 20-30 days interval.
• Within 15-30 days, the SNCs root and grow and by this time they are ready for transplanting in field or in polythene bags.
• The cuttings from polythene bags are subsequently transplanted in field after establishing for 15-20 days.
3. Multiplication Using Stem Cutting
• The method can produce 25-100 stem cuttings from a single mother plant in a period of 2-3 months.
• For getting maximum cuttings, big sized healthy tubers with multiple sprouts are planted shallow in pots and when the shoots are 10-15 cm tall, terminal growing tips are cut (decapitation) to promote growth of lower axillary buds.
• The axillary shoots are harvested after every 10-15 days by taking 4-6 cm long apical segments and leaving 1-2 leaves at the base for regrowth of axillary buds.
• The harvested stem cuttings are rooted on sand beds and then transplanted in field or polythene bags. d beds.
4. Multiplication Using in vivo Minitubers
• Small tubers (minitubers) commonly develop on old sprouted tubers in cold stores or country stores.
• Temperature in the range of 20-25 °C, 70-80 per cent relative humidity and darkness are conditions favourable for the development of minitubers.
• These tubers are like normal tubers and can grow into whole potato plant when planted in soil.
• There are two methods of producing minitubers.
• These are minituber production on sprouted mother tuber, and minituber production on leaf bud cuttings.
1. Minituber Production on Sprouted Mother Tubers
• It consists in producing multiple sprouts on mother tubers under diffused light.
• The tubers with multiple sprouts are then kept in black polythene bags at room temperature (18-24 °C) for 3-4 weeks.
• During this period, tuberization initiates and less than pea-sized tubers are developed.
• At this stage, the mother tubers are buried in moist sand in wooden trays and the trays are covered with black polythene sheet.
• Humidity is maintained by sprinkling water as and when required. After 8 weeks, minitubers of all sizes ranging from 30 mg to 4.3 g are developed on the mother tubers.
2. Minituber Production on Leaf Bud Cuttings
• For obtaining leaf bud cuttings, plants with multiple shoots are grown under long days (14-16 h light).
• The senescing plants are exposed to short days (8-10 h light) for 8-10 days before taking leaf bud cuttings.
• Leaf bud cuttings (3-4 cm long) with single node and attached leaf are cut from central part of such plants.
• These cuttings are planted in moist sand bed in such a way that the axillary bud is completely burried
5. Multiplication using in vitro Techniques
• Under present system of potato breeder seed production, indexing is done based on testing of a single scooped eye from a tuber.
• There are reports of inconsistent distribution of potato viruses within a tuber (Anand and Ganguly, 1964; Beemster, 1972).
• Therefore indexing does not assure complete virus freedom in indexed tubers and detection of some viruses is common during field testing in stage 1.
• Some of the advanced in vitro techniques developed to circumvent this problem in initial stages of seed production are (Wang and Hu, 1982)
1. Meristem — tip culture
2. Micro propagation and Micro tuber production
• Various workers have suggested possible integration of these innovations into conventional seed multiplication (Naik and Singh, 1988; Chandra and Dhingra, 1990).
• With the increasing trends in area under potato cultivation, it would not be possible for CPRI alone to meet the breeders’ seed requirement of the country even after integrating all these multiplication techniques in seed production.
• Hence, it is imperative to involve State Agricultural Universities and few other approved organizations in breeders’ seed production.
• Keeping in view the immediate requirement of quality seed, an operational scheme was proposed for meeting the demand.
• Under this scheme, the total pre basic seed would be produced at CPRI with available expertise and additional facilities.
• The breeders seed produced by CPRI is supplied to National Seeds Corporation, State Departments of Agriculture / Horticulture and other seed producing agencies for its subsequent multiplication as Foundation I, Foundation II and certified seed.