GENETIC MECHANISM OF SOME PHYSIO- MORPHOLOGICAL TRAITS OF BREAD WHEAT UNDER NORMAL AND HEAT STRESS CONDITIONS

Abstract

Two hundred and twenty bread wheat genotypes with diverse origin were preliminary evaluated under normal temperature and heat stress conditions under field condition. Four heat stress tolerant and three thermolabile wheat strains were selected on the basis of stress tolerance index and relative grain yield performance ratio. These seven genotypes were crossed in diallel fashion including reciprocals. F 1 progenies were evaluated in field and laboratory by laying out two set of experiments, according to RCBD with three replications, one each under normal and heat stress condition. All the agronomic practices were carried out as and when required. Various physio- morphological traits were studied On grand mean basis a considerable reduction in almost all attributes was observed in heat stress as compared to normal temperature regime except for canopy temperature depression and cell membrane thermostability, which showed 17.05 and 6.24 % increase under heat stress condition respectively. Additive gene action with partial dominance was revealed for days to heading, days to anthesis, spike index at anthesis, plant height, spikes per plant, spike length, grains per spike, 1000-grain weight, grain yield per plant, dry biomass per plant at maturity, grain set index, kernels per unit spike dry weight, CTD and CMT while overdominance type of gene action was observed for the attributes viz., spikelets per spike, days to maturity, dry biomass per plant at anthesis and harvest index. Out of seven parents, the best performance under both temperature regimes was showed by genotype BKR-02, which had the maximum value of grain yield per plant and most of its components. This parental genotype exhibited high spike index at anthesis, dry biomass per plant at anthesis, grain set index, number of grains per unit dry spike weight justifying high grain yield in heat stress. Considerable crosses under normal temperature regime were BKR-02 x SH-02, Ch-86 x SH-02, SH-02 x BKR -02 and SH-02 x Ch-86. However, in heat stress regime hybrids with best performance include BKR-02 x V00183, BKR-02 x SH-02, V00183 x Ch-86, SH-02 x BKR-02 and SH-02 x Ch-86. Similarly F1 hybrids as mentioned above registered good performance for various physio-morphological traits confirming the validity of techniques involved for determination of high yielding thermotolerant wheat genotypes for hot irrigated dry climate. Overall situation displayed the significant role of both additive and non-additive genetic variability suggesting the involvement of integrated heat stress breeding strategies which can potentially exploit the additive and non-additive genetic variability in stress free and heat stress conditions.