Foliage-applied sodium nitroprusside and hydrogen peroxide improves resistance against terminal drought in bread wheat

Terminal drought is threatening the wheat productivity worldwide, which is consumed as a staple food by millions across the globe. This study was conducted to examine the influence of foliage-applied stress signalling molecules hydrogen peroxide (H₂O₂; 50, 100, 150 μm) and nitric oxide donor sodium nitroprusside (SNP; 50, 100, 150 μm) on resistance against terminal drought in two bread wheat cultivars Mairaj-2008 and BARS-2009. These stress signalling molecules were applied at anthesis stage (BBCH 61); drought was then imposed by maintaining pots at 35% water holding capacity. Terminal drought caused significant reduction in grain yield of both tested bread wheat cultivars; however, foliage application of both stress signalling molecules at either concentration improved the performance of both bread wheat cultivars. Maximum improvement in 100-grain weight (12.2%), grains per spike (19.7%), water-use efficiency (WUE; 19.8%), chlorophyll content index (10.7%), total soluble phenolics (21.6%) and free leaf proline (34.3%), and highest reduction in leaf malondialdehyde contents (20.4%) was recorded when H₂O₂ was foliage-applied at 100 μm. Foliage application of SNP enhanced the grains per spike, 100-grain weight and grain yield by 14.9%, 11.3% and 20.1%, respectively, than control. The foliage-applied stress signalling molecules improved the accumulation of soluble phenolics, proline and glycine betaine with simultaneous reduction in malondialdehyde contents, which enabled wheat plants to sustain the biological membranes under stress resulting in better stay green (high chlorophyll contents) under drought. This helped improving the grain number, grain weight, grain yield, WUE and transpiration efficiency. In crux, foliage-applied H₂O₂ and SNP, at pre-optimized rate, may be opted to lessen the drought-induced yield losses in bread wheat in climate change conditions.