Genetic analysis of drought responsive physiological characters in coconut

Coconut (Cocos nucifera L.) is mainly grown as a rainfed crop and experiences drought during summer months. Earlier studies identified the physiological traits responsible for drought tolerance in coconut. For the first time an attempt is made to understand the genetics of these characters. Coconut cultivars (two Dwarfs- CGD and MYD; four Talls-ECT, PHOT, LCT and FMST) with desirable characters were selected and crossed in a 2 x 4 line x tester mating design to study the combining ability and gene action with respect to drought responsive physiological traits. Physiological parameters like leaf water potential, transpiration rate, net photosynthetic rate (P-n) and lipid peroxiclation were recorded in seedlings under non-stress, water stress and recovery conditions. Analysis of variance for combining ability revealed significant differences among parents and hybrids for all characters. Seedling transpiration rates and leaf water potentials showed higher specific combining ability (SCA) effects than general combining ability (GCA) effects due to predominance of non-additive gene action indicating heterosis for this character. The Pn under stress was additive with good combining ability, while the Pn during non-stress and recovery were governed by non-additive gene action that can be exploited for heterosis. In case of lipid peroxidation, gene action was unpredictable in non-stress with additive gene action being nil with low dominance. Whereas, during stress and recovery, non-additive gene action was observed. These results indicate the possibility of exploiting the nature of gene action governing drought sensitive traits in breeding for tolerant coconuts.