Screening of wheat genotypes for heat tolerance under terminal heat stress in Sudan

Wheat production in Sudan faces one of the most severe heat stress environments in the world. The Khartoum-Gezira production zone experiences mean temperatures above 32 °C during the grain filling period (February-March), with maximum daily temperatures frequently exceeding 40 °C conditions that severely reduce grain set, accelerate senescence, and limit productivity to a fraction of the crop's genetic potential. Developing and identifying heat-tolerant wheat genotypes is the most cost-effective strategy for sustaining wheat production in this environment. This research was conducted at the Khartoum Institute of Cereal Research, Khartoum, Sudan, across the 2022 and 2023 winter seasons, to screen 25 wheat genotypes for heat tolerance using the Heat Susceptibility Index (HSI), Heat Tolerance Index (HTI), Canopy Temperature Depression (CTD), SPAD chlorophyll index, membrane stability index (MSI), and grain yield under heat stress and non-stress conditions. Genotype G-14 produced the lowest HSI (0.42), highest HTI (0.88), highest grain yield under heat stress (3.84 t ha-1), and maintained the smallest canopy temperature difference (+1.6 °C above ambient versus +8.4 °C for the most susceptible genotype). Genotypes G-25 (HTI 0.82), G-11 (HTI 0.74), and G-18 (HTI 0.71) also showed acceptable heat tolerance. Canopy temperature was the most reliable single-trait indicator of heat tolerance (correlation with yield r = -0.88). These findings identify priority genotypes for advancement in Sudanese wheat breeding programmes and provide a validated screening protocol for heat tolerance that can be applied across CGIAR winter wheat nurseries targeting hot drylands.