Exogenous application of thiourea improves the performance of late sown wheat by inducing terminal heat resistance

This study was conducted to evaluate the potential of thiourea in improving the terminal heat resistance in bread wheat. Four wheat genotypes PBW 550 and PBW 343 (heat sensitive) and C 306 and C 273 (heat resistant) were field sown at normal time (November) or late (December) to expose the crop to heat stress during grain-filling. Temperature during grain filling was ~25.6°oC in normal and 29.4°C in late sown wheat crop. Prior to sowing, wheat seeds were soaked in 6.6 mM thiourea solution) for 6 h. Thiourea was also applied as foliar spray (6.6 mM) at anthesis. Heat stress, during grain filling, led to disruption of cellular membrane by increasing membrane injury index, lipid peroxide and H₂O₂ contents. Nonetheless, heat resistant (C 306 and C 273) genotypes had lower lipid peroxidation and membrane injury owing to better expression of antioxidants. However, thiourea application ameliorated the heat-induced damages by stimulating the total antioxidant activity through decrease in lipid peroxidation and membrane injury. Thiourea application also increased the total soluble proteins, amino acids and chlorophyll contents in all the tested genotypes. This all caused substantial increase in plant height, peduncle length, peduncle weight and grain weight. Genotypes PBW 550 and PBW 343 showed higher grain weight in spite of greater injury to membranes over genotypes C 306 and C 273. Combined application of thiourea as seed treatment and foliar spray was more effective in improving the wheat performance by enhancing membrane stability, antioxidant potential and yield components.