Physiological and phenological responses of wheat to terminal heat stress under foliar application of salicylic acid and thiourea

The present investigation was conducted during the rabi season of 2019-2020 at the Seed Technology Research Farm, Jawaharlal Nehru Krishi Vishwa Vidyalaya (JNKVV), Jabalpur, Madhya Pradesh, India to evaluate the influence of terminal heat stress and foliar application of bioregulators on pheno-physiological traits of wheat (Triticum aestivum L.). Two varieties, JW-3211 and JW-3382, were evaluated under normal and late-sown conditions with foliar sprays of thiourea (TU) and salicylic acid (SA) at 400 and 800 ppm concentrations. Significant variations were recorded among varieties, sowing dates, and treatments for all phenophases and physiological parameters. Late sowing accelerated phenological development, with earlier ear emergence (48.55 DAS), shorter grain filling duration (40.81 DAS), and reduced field maturity (108.24 DAS) compared to normal sowing (58.70, 44.14, and 118.19 DAS, respectively). Heat stress reduced grain filling duration by 7.57% and maturity period by 17% over normal conditions. Among genotypes, JW-3211 exhibited superior adaptability, showing earlier ear emergence (55.00 DAS), shorter maturity (109.76 DAS), and higher physiological efficiency. Foliar application of SA @ 800 ppm and TU @ 800 ppm enhanced leaf area index (4.27), leaf area duration (7344.28), and chlorophyll content index, thereby improving photosynthetic activity and delaying leaf senescence under heat stress. The interaction effects indicated that JW-3211 under late sowing with SA @ 800 ppm maintained higher LAI and chlorophyll stability, reflecting better heat tolerance. Overall, foliar application of bioregulators, particularly SA and TU at 800 ppm, effectively mitigated the adverse impact of high temperature by stabilizing physiological processes and extending photosynthetic duration, contributing to sustained wheat performance under terminal heat stress conditions.