Assessing the efficacy of synthetic compounds foliar sprays in alleviating terminal heat stress in late-sown wheat (Triticum aestivum)

Detrimental effects of terminal heat stress could be mitigated by exogenous application of synthetic compounds by preserving cell membrane integrity and protecting against oxidative damage. A field experiment was conducted to test the application of seven synthetic compounds on wheat growth traits: (1) thiourea (20 mM and 40 mM); (2) potassium nitrate (1% and 2%); (3) sodium nitroprusside (400 mu g mL-1 and 800 mu g mL-1); (4) dithiothreitol (25 ppm and 50 ppm); (5) salicylic acid (100 ppm and 200 ppm); (6) thioglycolic acid (200 ppm and 500 ppm); and (7) putrescine (4 mM and 6 mM). These compounds were applied at the anthesis and grain-filling stages to enhance physio-biochemical traits and yield attributes of wheat (Triticum aestivum) cvs GW-11 and GW-496 under terminal heat stress. The results indicated that GW-11 plants treated with 100 ppm salicylic acid exhibited significant improvements (P <= 0.05) in canopy temperature depression, proline content, total chlorophyll content, and the membrane stability index. Compared with the control treatment, foliar application of 100 ppm salicylic acid at both stages caused increases in grain yield (19.5%), followed by a 14% increase with 4 mM putrescine. These yield improvements were attributed to higher grains per spike, more effective tillers, and greater 1000-grain weight, reflecting enhanced sink capacity and grain development under stress. Consequently, the foliage application of 100 ppm salicylic acid at the anthesis and grain-filling stages is recommended to improve late-sown wheat productivity and reduce terminal heat stress.