a.naznin@westernsydney.edu.au, j.he4@westernsydney.edu.au, yuanyuan.wang@westernsydney.edu.au, a.abbas@westernsydney.edu.au, o.dauda@westernsydney.edu.au, k.ning@westernsydney.edu.au, o.ghannoum@westernsydney.edu.au, j.bose@westernsydney.edu.au, z.chen@westernsydney.edu.au

The constant increase in global temperatures due to climate change poses a significant threat of heat stress, affecting both plants and human livelihood. Heatwaves are becoming more frequent and intense, threatening food security and crop productivity, especially in major staples like wheat, faces substantial challenges due to fluctuating environmental conditions.

Originally, wheat is a crop in temperate regions, facing various hurdles when grown in tropical or subtropical areas. Considering this, our research undertook a comprehensive assessment of 319 wheat genotypes under both field and controlled glasshouse conditions at elevated temperatures. The aim was to evaluate phenotypic variations in leaf structure and other pertinent physiological and agronomical traits, with a focus on identifying quantitative trait locus (QTL) related to heat tolerance in wheat.

Numerous physiological, agronomic and yield related characteristics were measured. The plant growth, morphology and physiology were found to be changed under heat stress condition. An increase in leaf temperature (Tleaf), chlorophyll content, transpiration rate (Tr), leaf vapor pressure deficit (VPD) and vein density (VD) has observed under heat stress condition.

On the other hand, leaf thickness and leaf size found to be reduced under heat stress. Chlorophyll content, Tleaf, normalized difference vegetation index (NDVI), Tr and VD were found to be involved in facilitating the stress responses. We conducted a genome-wide association study (GWAS) to identify QTLs associated with leaf structural, physiological, and agronomic traits. Wheat population (189 genotypes) genotyped with Diversity Array Technology (DArT) polymorphic markers and several QTLs were identified related to leaf traits.

Our analysis revealed 166 markers linked to Tleaf, 160 markers correlated with VPD, 2 markers related to NDVI, 3 markers linked to biomass, and 1 marker related grain yield under field conditions. These QTLs are distributed across chromosomes 1A, 2B, 4A, 4B, 5A, 5B, 6A, 6D, and 7A. Notably, we identified 11 significant QTLs (LOD > 4.5) for Tleaf and 9 significant QTLs for VPD.

The phenotypic variability explained by these QTLs ranged from 17.5- 19.6% for Tleaf, 17.5- 21.1% for vpd, 10.3-11.7% for NDVI and 11.2-15.4% for biomass. Candidate genes related to heat stress tolerance, particularly from the regions of these significant QTLs, will be further identified. Subsequent validation of these QTLs and candidate genes can facilitate their utilization in marker-assisted selection and breeding programs.

This approach aims to develop wheat varieties with enhanced stability in grain yield under high temperatures, thereby contributing to sustainable crop production in challenging environments.