Physiological basis of heat tolerance in late-planted wheat genotypes under terminal heat stress

Abstract:

Nearly 40% of the global wheat area faces terminal heat stress, yet physiological screening criteria for heat tolerance remain poorly standardized. This research assessed eight wheat genotypes planted late (December 15) at Rajshahi Agricultural University, Bangladesh, during rabi 2022–23 and 2023–24 to identify reliable physiological markers of heat tolerance under field conditions. A randomized complete block design with three replications was used. Membrane stability index (MSI), chlorophyll content index (CCI), canopy temperature depression (CTD), proline accumulation, and grain filling rate (GFR) were measured at anthesis and 15 days post-anthesis. Maximum temperatures during grain filling exceeded 35 °C on 23 days in 2023 and 27 days in 2024. Genotypes DBW-187 and HD-3226 consistently recorded the highest MSI (72.8% and 71.3%), CTD (6.7 and 6.2 °C), and GFR (1.91 and 1.83 mg day⁻¹). MSI showed the strongest correlation (r = 0.89) with grain yield under stress. A composite heat tolerance index combining MSI, CTD, and GFR explained 83.7% of yield variability. These results suggest that MSI-CTD-GFR screening can accelerate identification of heat-tolerant wheat lines for late-sown environments.