Physico-biochemical traits and differential expression of genes linked with terminal heat tolerance in bread wheat ( Triticum aestivum L.)

Plant Breeders have the critical challenge of increasing the productivity of bread wheat as a result of several environmental challenges particularly terminal heat stress which affects the plant especially at reproductive stage. In the present investigation, the physiological and biochemical responses of 51 advanced breeding lines of bread wheat developed by ICAR-IIWBR, Karnal, India, along with 5 national check varieties (DBW14 and WR544 as tolerant check, whereas HD2967, RAJ3765, and Sonalika as a susceptible check) have been documented. The field experiment was carried out at ‘AB’ block farm of Bidhan Chandra Krishi Viswavidyalaya (BCKV), Kalyani, West Bengal, India, in three consecutive years during rabi season from 2017–2018 to 2019–2020. The expression of two stress-associated genes viz., HSP90 and WRKY72a were also assessed under terminal heat stress in selected superior lines concerning physico-biochemical responses. Reduction in relative water content (17.94%), chlorophyll content (0.16%), membrane stability index (6.62%) and pollen viability (7.5%), whereas increases in proline (77.64%) and Malondialdehyde content (2.49%) were observed due to exposure to terminal heat. A significant increase in expression profiling (~ 1.45-fold increase in HSP90 gene and ~ 1.6-fold of WRKY72a) was observed in all selected terminal heat-tolerant genotypes. Based on the clustering pattern with tolerant check, as well as considering the heat susceptibility index (HSI < 0.5) 7 breeding lines viz., NEST17.15, NEST17.26, NEST17.17, NEST17.35, NEST17.14, NEST17.43, NEST17.22 were identified as the potent terminal heat-tolerant lines which could be utilized for developing wheat varieties to combat with forthcoming climate vagaries.