Emails: Z.Chen@westernsydney.edu.au; J.He4@westernsydney.edu.au

In wheat, high temperature accelerates leaf senescence and shortens the crop cycle - limiting the opportunity for plant photosynthesis and accumulation of carbohydrates in grains. Understanding the response of wheat to heat stress in the context of source-sink relationship (e.g. plant phenotypic traits, leaf structural and biochemical traits, spikelet fertility, and seed morphology) is critical for maintaining high yields under heat stress.

In this study, we evaluated 319 wheat genotypes in both controlled greenhouse conditions and field settings during the 2023 growing season. The objectives were to examine the performance of these genotypes under heat stress and to develop rapid heat tolerance screening methods.

We found that leaf vapour pressure deficit, leaf temperature, stomatal conductance as well as stomatal density and index, linear electron flow, normalized difference vegetation index are reliable indicators that can be used for screening heat tolerance in wheat. A weighted ranking system was developed based on performance metrics across the assessed traits, facilitating the identification of genotypes with superior heat resilience.

Our findings highlighted 16 genotypes, including Aus19402, Caz53, and Vulcan, that demonstrated robust tolerance to heat stress. These genotypes exhibited significantly lower leaf temperatures and higher stomatal conductance, suggesting effective physiological adaptations for maintaining homeostasis under elevated temperatures.

These findings are critical for wheat breeding programs aimed at enhancing heat tolerance. Incorporating these insights into breeding strategies can help develop wheat varieties that maintain high yields under increasing temperatures. As the next step, the project team will is evaluating QTLs, haplotypes, and genes to understand the molecular and genetic basis of source-sink relationship in regulating heat tolerance of wheat.