How Do Drought, Heat Stress, and Their Combination Impact Stem Reserve Mobilization in Wheat Genotypes?

Abstract

Drought and heat stresses represent the primary agricultural challenges in arid and semiarid regions globally. In wheat, among the most vulnerable stages to these stresses is the grain-filling process. This critical phase relies heavily on photosynthesis during the late growth stage and the mobilization of stem reserves. This study evaluated 60 spring wheat lines from the CIMMYT-Mexico Core Germplasm (CIMCOG) panel alongside four Iranian wheat cultivars under normal, drought, heat, and combined drought and heat stress conditions in two growing seasons. Several agronomic traits, including those associated with stem reserve mobilization, were assessed during the study. The combined analysis of variance revealed significant impacts of both independent and combined drought and heat stresses on the measured traits. Moreover, these stresses influenced the inter-relationships among the traits. High-yielding genotypes were identified through a combination of ranking and genotype and genotype by environment (GGE) biplot analysis. Among the top 40 genotypes, 21 were identified as environment-specific, while 19 remained common across at least two environments. Environmental dependence of grain yield responses to the sinks including stem reserve mobilization and spike reserve mobilization was found. Utilizing a machine learning algorithm, a regression tree analysis unveiled specific traits—including grain filling and canopy temperature—that contributed significantly to the high-yielding features of the identified genotypes under the various environmental conditions. These traits can serve as indirect selection criteria for enhancing yield under stressful conditions and can also be targeted for manipulation to improve wheat stress tolerance.