PHYSIOLOGICAL CHANGES IN WHEAT UNDER LATE PLANTING HEAT STRESS

Abstract

In laboratrory experiment six wheat genotypes (Aghrani, Kanchan, CB-30, Sonora, CB-24 and CB-34) were germinated to study seed metabolic activity and reserve translocation at 15, 25 and 35°C. Among the genotypes four genotypes e.g., Aghrani, Kanchan, CB-30 and Sonora were tested under normal and post anthesis heat stress condition by seeding at November 30 and December 30 to evaluate the physiological changes in relation to heat stress. Speed of germination was influenced by temperature. Seed reserve translocation and seedling growth of Sonora, CB-24 and CB-34 were found to be more affected by the change of temperature than Aghrani, Kanchan and CB-30. Although Sonora, CB-24 and CB-34 showed higher seed metabolic efficiency than rest of the genotypes at 25°C, the efficiency of these genotypes reduced more both at 15°C and 35°C as compared to Aghrani, Kanchan and CB-30. Time to exceed 50% membrane leakage was about four times longer in Aghrani, Kanchan and CB-30 (120-150 min.) and the genotypes were grouped as heat tolerant (HT) than in Sonora (30 min) which considered as heat sensitive (HS). Due to post anthesis heat stress condition the HS genotype Sonora in comparison to heat tolerant (HT) genotype exhibited larger decrease in kernel proline (47.2%) along with larger increase in flag leaf proline (122%). Irrespective of growing conditions, both dry matter and starch accumulation in kernel showed a typical sigmoidal pattern in all genotypes. Due to post anthesis heat stress, the quantity of dry matter accumulation at peak and duration required to attain peak was higher in HT genotypes than the sensitive one. Sonora, a HS genotype, responded to post anthesis heat stress by acccumulating larger quantity of soluble sugar during active kernel development period in contrast to HT genotypes indicating poor capacity of kernel of Sonora to utilize sugar for starch synthesis. The heat tolerant genotypes exhibited distinctly higher relative individual kernel dry weight, higher kernel number per spike, higher relative grain yield and low susceptibility index for grain yield under post anthesis heat stress condition compared to heat sensitive genotype. Finally, grain yield was found to be reduced by about 2.6 to 5.8% in HT genotypes and 7.2% in HS genotype for each 1°C rise in average mean air temperature from normal growing condition during anthesis to maturity.