Combining Ability and Gene Action Studies for Heat-tolerance Physio-biochemical Traits in Tomato
High temperature disrupts normal physiological functions of plant and affects its growth and development. A 5×5 diallel cross in tomato (Lycopersicon esculentum) showed Nagcarlan to be the best combiner for heat-tolerance traits. The crosses involving high General Combining Ability (GCA) parents also showed good Specific Combining Ability (SCA) effects. Heat-tolerance traits were governed by both additive and non-additive gene action. Total chlorophyll content and nitrate reductase activity were governed by dominant gene action and had more dominant genes than recessive genes for heat tolerance. Pollen viability, relative leaf water content and chlorophyll stability index were governed by both additive and dominant gene action. These traits could be used in the pure line selection to accumulate more additive effects. The Wr-Vr graph indicated over-dominance for heat tolerance. Moderate narrow-sense heritability h2 (ns) was found for pollen viability (0.44) and total chlorophyll content (0.43). Heterosis breeding was appropriate to utilize the dominant gene action involved for heat tolerance.