Characterization of Traits Associated with Grain Yield Under Terminal Heat Stress in Bread Wheat (Triticum aestivum L.) on the Basis of Heat Susceptibility Index

High temperature affects various morpho–physiological and agronomical traits in wheat crops. High-temperature stress can cause poor seed growth, reduction in grain filling duration and grain number, root growth and yield reduction. For the identification of heat tolerant genotype, fifteen wheat cultivars were evaluated under timely and late sown conditions based on grain yield in 2018–2019 crop seasons by precise phenotyping approach for this study. Heat susceptibility index (HSI) value recorded for grain filling duration and canopy temperature ranged from 0.57 to 1.35 with a mean value of 1.00 and 0.58–1.29 with a mean value of 1.005, respectively. Grain no./spike and grain weight/spike HSI values ranged from 0.28 to 1.60 (mean value 1.004) and 0.81–1.21 (mean value 0.99), respectively, with thousand-grain weight values ranging from 0.64 to 1.18 (mean value 0.98). Two (WH730 and HUW468) genotypes showed tolerance to heat in all traits, and five genotypes (K7903, RAJ4079, Hindi62, PBW723 and HD3086) showed tolerance in either one trait or none depicting them as sensitive to high temperature.