Different propagation techniques of Potato

Seed plot technique

       This technique of seed production envisages raising a crop (using healthy seed) during the period when aphids (vectors of virus diseases) population is very low, taking precautions of use of insecticides and periodic roguing of diseased plants, and finally dehaulming the crop before the aphids reach the critical level of 20 aphids/100 compound leaves. The seed potato produced in the plains gives better plant stand and yield in all the potato-growing regions because of its better physiological age for giving quick emergence and faster growth of haulms. Thus the seed produced in the north-western plains and kept in cold stores during April–September is the most useful potato for planting in the plains, particularly when early crops are to be raised. Cold-stored seed cannot withstand transport over long distances in the plains during September–October. If it is necessary, care has to be taken not to transport the seed in closed wagons over a long period. After it is removed from the cold storage, the seed should be dried and carefully sorted. This post-cold-storage treatment is necessary to get rid of the problem of ‘sweating’ and brings about respiratory equilibrium of tubers.

Use of hill-grown seed

      The potato in northern hills is harvested in September/October which is also the time of planting of the main crop in north-western Indian plains. But, being dormant or partially dormant, these tubers cannot be used immediately for seed purposes. The hilly seed could, however, be used with advantage, after breaking dormancy, in regions where planting is delayed beyond first week of November. It is also used for planting the spring crop in north-western region. For breaking the tuber dormancy, seed tubers are soaked in 1% thiourea + 1ppm gibberellic acid solution for 1 hr.

Seed size and spacing

All sizes of tubers can be utilized as seed but medium-sized (25–55mm or 25–75g) often called as seed size is better than other grades. Even in seed size, tubers of 35–40mm or 45–50g are ideal. Comparable yields can be obtained by planting medium-sized tubers (35–45mm) at 60cm × 20cm spacing and large-sized tubers (45–55mm) at 60cm × 25cm spacing keeping the plant populations at 83,000 and 67,000 plants/ha, respectively. For small-sized seed (25–35mm), a population of 1,11,000 plants/ha (60cm × 15cm inter- and intra-row spacings) is ideal.

         The potato yield increases with increase in seed rate. The optimum seed rate for getting high yield is 20–25q/ha for 15g seed, 25–30q/ha for 30g seed and 30–35q/ha for 45g seed size.

          Use of large-sized tubers increases the seed rate. However, for planting early and main crops in plains, where cold-stored seed is used, it is advisable to use only whole seed, as several saprophytic organisms often establish on the cut surface of the tubers causing seed piece decay, leading to poor and gappy germination. In plateau region of southern India, which depends on seed potatoes from north Indian hills, the large tubers can be cut and planted late in November. For spring crop in north-western plains, for which the seeds are procured from the hills, the cut potatoes are used as seed. The seed tubers are cut about a week or 10 days before planting and treated with fungicides (dipped for 10 minutes in 0.2% solution of Mancozeb) and spread at a cool and moist place, so that the cut surface suberizes and seed pieces do not rot.

Pre-sprouting of seeds

         Pre-sprouting of tubers before planting ensures multiple, stout and healthy sprouts which help in quick emergence and uniform stand of crop. It also increases the number of tubers and leads to larger proportion of seed-sized tubers. For pre-sprouting, the tubers are kept in shade in diffused light in baskets or trays or spread in thin layer on the floor. Seed stocks are examined twice a week to remove rotten tubers. Seed tubers when removed from the cold store, are generally dormant and give low yields, when planted immediately. One week pre-sprouting period is sufficient for all sizes of tubers in north-western plains and of 3 weeks in eastern plains.