PRODUCTION AND PERFORMANCE OF POTATO MINI-TUBERS

Production of mini-tubers as a source for seed potato was investigated by growing in soil micropropagated plants and micro-tubers produced from micropropagated plants. Cultures of several cultivars were initiated from indexed tubers and multiplied on modified MS medium. Cultures were micropropagated by using a modular system which allowed batch handling. Micropropagated plants produced mini-tubers in glasshouse after 70-115 days of growth in soil. A large proportion of the mini-tubers produced were between 9 and 15 mm diameter. Several factors, e.g., explant number, duration of in vitro culture and genotype influenced mini-tubers production. Micropropagated plants after culture of 86 days or longer produced micro-tubers ca. 2 to 10 mm diameter. Plants, which formed micro-tubers in vitro, produced less number of mini tubers in soil. Micro-tubers produced I to 3 mini-tubers when grown in soil in chain-type paper pots, but produced conventional sized tubers when grown in soil under plastic polytunnel. Mini-tuber number varied widely between potato cultivars; cvs. Bintje and British Queen produced more mini-tubers than the other cultivars. Mini-tubers developed green hard skins when kept in light for 3 weeks, and could be stored in dark at 4 degrees C upto 6 months. In a field trial, small mini-tubers ca. 5-10 mm diameter produced more but smaller tubers than mini-tubers ca. 15-20 mm diameter. The micropropagated plants and the plants grown from mini-tubers were genetically stable, and did not show any morphological aberrations except for one variegated plant among the several thousand produced. It is concluded that the production of mini-tubers by soil planting of micropropagated plants is a rapid and efficient method for producing seed potato tubers.