Keywords: heat stress, malondialdehyde, proline, superoxide dismutase, timely and late sown condition, wheat genotypes thermostability, canopy function, stable green habit, better mobilization rate of food reserve and other technical or physiological parameters might be helpful to overcome yield loss under terminal heat stress. 12 In vitro studies of wheat plants in combination with genetic manipulation to develop heat tolerant wheat are of limited success. Therefore, the complex physiological-genetic approach could be useful to acquire heat tolerance in wheat to minimize the farmer's risk for reduced yield and low quality grain product. Here, Physiological evaluation of wheat genotypes was performed under timely and late sown condition.
Results
Estimation of chlorophyll index (SPAD-values), leaf area index (LAI) and proline content. Chlorophyll content (SPAD-values)of wheat genotypes viz., DBW-140, RAJ-3765, PBW-574, K-0-307 and HS-240 under timely and late sown was calculated after 30, 50, 70, 90 and 110 d. It was found that SPAD-values affected under timely and late sown conditions were 41.5, 38.9, 37.08, 37.67, 47.7, 47.59, 46.56, 46.73, 41.03, 40 and 40.15, 34.5, 34.76, 33.33, 45.63, 44, 43.03, 42.52, 4,137 and HS-240 genotypes showed highest reduction in LAI (0.3, 1.36, 3.78, 3.0 and 0.37, 2.08, 3.94, 3.29) at 30, 70 and 90 d after sowing, respectively (Fig. 1B). The proline content (μg g −1 FW) was found to be increased in all the genotypes studied (30.25, 160.5, 135.2, 262.1, 184.0 and 221.68, 236.55, 261.77, 419.35) under late sown condition as compared with that of timely sown condition (89.6, 106.8, 119.6, 62.0 and 21.98, 20.66, 37.0, 20.86, 18.37) at both anthesis and 15 DAS, except , respectively (Fig. 1C).Evaluation of malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, heat susceptibility index (s) (HIS) and yield associated traits. The amount of malondialdehyde (MDA) (μ mole g −1 FW) produced when polyunsaturated fatty acids in the membrane undergone lipid peroxidation in wheat genotypes were calculated as 13. 06, 11.80 and 7.26, 4.23 in HS 240 and K-0-307 genotypes respectively at the time of anthesis in late sown and timely sown conditions. The similar trends were also observed in HS 240 and K-0-307 genotypes 15 DAS, which followed by Raj 3765, DBW 140 and PBW 574 genotypes ( Fig. 2A). There is no significant increase in superoxide dismutase (SOD) activity (unit mg −1 FW) in genotypes evaluated at anthesis stage under timely and late sown conditions. In contrast, after 15 d of anthesis SOD activity was highest in RAJ-3765 (1.88) whereas in HS-240 and K-0-307 genotypes it was lowest (1.63 and 1.60) under late sown condition (Fig. 2B). The heat susceptibility index (HIS) of HS 240 and K-0-307 wheat genotypes was highest (1.33, 1.57, 1.51 and 1.17, 1.34, 1.65), which followed by DBW 140, Raj 3765 and PBW 574 genotypes (0.846, 0.649 and 0.411), (0.780, 0.905 and 0.905) and (0.897, 0.457 abd 0.682) for 1000-grain weight, grain weight and grain yield, respectively (Fig. 2C). Y...
