EVALUATION OF HEAT TOLERANT POTATO HYBRIDS UNDER TROPICAL CONDITIONS IN KERALA

temperate climates. Bushnell (1) defined 17°C as the optimum mean temperature for tuberization in potatoes. Night temperatures above 20°C severely depress both tuber initiation and bulking, and temperatures above 25°C effectively stop tuber production (6). Potato tuberization is also reported to depend largely on the night temperature and not on the average daily temperature (5). In lowland tropics, including peninsular India, high day and night temperature are the major considerations resulting in loss of tuber yield (2) due to reduced partitioning of assimilates to tubers. In India potato crop is grown mainly when the day temperature is below 30°C and night temperature is below 20°C. In order to develop heat tolerant potato varieties crosses were made amongst known heat tolerant and local high yielding genotypes, and the progeny was screened by their ability to form tubers within one month after shifting to high temperature (5).