COMBINING ABILITY AND GENE ACTION FOR FRUIT YIELD AND HEAT TOLERANCE IN TOMATO (Lycopersicon lycopersicum Mill.) UNDER HEAT STRESS CONDITIONS.

Heat stress causes significant fruit yield loss in tomato (Lycopersicon lycopersicum Mill.). Breeding tomato varieties hybrids tolerant to high temperature will reduce fruit yield losses due to heat stress in Nigeria. Combining ability and gene action for fruit yield and heat tolerance was studied under heat stress conditions in tomato. The experiments were carried out at National Horticultural Research Institute, Bagauda Station farm (11°33´N; 8°23´E) and the Institute for Agricultural Research farm, Samaru (11011´N; 07038’E) between July to October, 2014 rainy season. Two heat tolerant and four susceptible tomato genotypes were crossed in a half diallel mating design. The results of combining ability analysis indicated that, both additive and non-additive actions were important for the inheritance of the traits. However, SCA variance components were higher than GCA variance components, indicating preponderance of dominance gene action for genetic control of the majority traits. The average degree of dominance values revealed over-dominance gene action for the most traits. The parent Icrixina was the best general combiner for the majority of the traits among the parents, while Petomech × Roma Savana and Icrixina × Rio Grande were the most desirable cross combinations for fruit yield per plant and percentage fruit set. Overall results indicated that hybrid vigor exploitation could be harnessed to produce high yielding and heat tolerant tomato hybrid under rainy season.