Morpho-Physiological and Biochemical Responses of Eight Bread Wheat (Triticum aestivum L.) Genotypes to Terminal Heat Stress Under Timely and Late Sown Conditions

Abstract

Terminal heat stress driven by global warming is among the most serious constraints to wheat productivity, particularly in the Indo-Gangetic plains where late planting exposes the reproductive phase to high temperature. A field experiment was conducted during the rabi season of 2024–25 at Swami Vivekanand Subharti University, Meerut, to evaluate eight bread-wheat genotypes (K-65, K-816, K-8434, K-9351, PBW-154, PBW-343, PBW-550 and PBW-226) under timely sown (control; 25 November) and late sown (terminal heat stress; 15 December) conditions in a factorial randomized design with three replications. Yield and yield-contributing traits, leaf chlorophyll (SPAD), and the osmolytes proline and total soluble sugar were recorded and analysed by two-factor analysis of variance. Late sowing significantly (p = 0.01) reduced plant height, tillers plant –1, spike length, spikelets spike –1, grains spike –1, 1000-grain weight, days to maturity and grain yield plant –1, the largest mean reductions occurring for days to maturity (˜11.0%) and grain yield (˜10.2%). Conversely, proline and total soluble sugar increased markedly under heat stress (overall increases of ˜53% and ˜54%, respectively), reflecting active osmotic adjustment. Genotype, sowing date and their interaction were significant for almost all traits. PBW-550 was the most heat-tolerant genotype—recording the smallest reductions in yield, grain weight and chlorophyll together with the highest osmolyte accumulation—followed by K-9351 and K-816, whereas PBW-343 was the most susceptible. Grain yield under late sowing was positively associated with retained chlorophyll and osmolyte accumulation. PBW-550 is therefore recommended for late-sown, heat-prone environments.