GENETICS OF HEAT TOLERANCE FOR FLORAL AND FRUIT SET TO HIGH TEMPERATURE STRESS IN TOMATO (Lycopersicon esculentum Mill.)

Three consecutive field evaluations were conducted to screen 38 tomato genotypes for tolerance to high temperature stress during spring-summer season (February to May) at day temperature range of 27.3-42.3 degrees C and 13.8- 22.9 degrees C night temperature, the average day/night temperature being 34.5/19.2 degrees C. Heat stress resulted in abnormal hastening in flowering (34%), and marked reduction in number of trusses/plant (35%), number of flowers/truss (25%), fruit set/truss (53%), and fruits/plant (71%) compared to that recorded in autumn-winter season under optimal temperature conditions. Of the 16 genotypes that set fruits in high temperature stress three lines viz., CLN 2413R, CLN 2116B, and COML CR-7 emerged as heat tolerant genotypes considering pollen viability, pollen germination, fruit set, and fruit yield/plant. These three lines along with two highly heat susceptible varieties - Patharkuchi and Ratan - were crossed in all possible combination, excluding reciprocals. The data was subjected to Hayman's model of diallel analysis. Both additive and dominance genetic variance were important for fruit yield/plant and other important characters like days to flower, flower/truss, fruit set/truss, pollen viability, pollen germination, fruits/plant, fruit weight, however, and dominance component was higher in magnitude for the other character. Over-dominance was revealed for most of the characters and partial dominance for days-to-flower, trusses/plant, and pollen viability which amply suggested the importance of non-additive genetic component for the expression of characters influencing heat tolerance. One or two dominant gene groups controlled the inheritance of the traits under study. Single plant selection will not be effective because narrow sense heritability estimates for most of the traits were low. Considering the results of the present investigation, it can be concluded that selection for high temperature fruit set should be based primarily on replicated family testing in the F(3) and later generations.