Integrating Agronomic Traits and Physiological Responses for Drought Resistance Screening in Wheat Germplasms

Drought stress is a critical limiting factor for wheat yield. Wild relatives of wheat have proven to be valuable genetic resources for desirable traits. This study aimed to conduct a comparative analysis of agronomic traits, photosynthetic physiological parameters, and antioxidant components among 26 heterogermplasm wheat cultivars under well-watered (WW) and water-stressed (WS) conditions over two consecutive years. The results revealed that all nine agronomic traits were adversely affected under WS conditions. Four agronomic traits were selected based on the drought-resistance coefficient (DC < 0.8) and heritability (H² < 0.7) to calculate the membership function value of drought resistance (MFVD), including flag leaf area (FLA), tiller number (TN), grain yield per plant (GYPP), and biomass per plant (BMPP). All wheat genotypes clustered into three groups based on their mean value of MFVD in two years. Under drought stress, wheat germplasms classified within the high MFVD group demonstrate significantly enhanced drought adaptability, as evidenced by superior photosynthetic performance with elevated photosynthesis rate (Pn), the actual photochemical quantum efficiency of photosystem II (ΦPSII), and the electron transfer rate (ETR), increased chlorophyll retention (higher SPAD values), strengthened antioxidant enzyme activities, and reduced stomatal limitation. Correlation analyses further reveal that MFVD exhibits significant positive correlations with Pn, ΦPSII, ETR, SPAD, and key antioxidant enzymes, while displaying a significant negative correlation with stomatal limitation value (Ls). These consistent physiological and biochemical patterns corroborate that the constituent agronomic traits-tiller number (TN), flag leaf area (FLA), biomass per plant (BMPP), and grain yield per plant (GYPP)-serve as robust and integrated phenotypic indicators for comprehensively evaluating drought resistance in wheat germplasm. Among the evaluated lines, lines 6, 15, 17, 21, and 22 exhibited significantly higher levels of drought resistance. These results highlight the presence of genetic variability among heterogermplasm wheat cultivars, which can be harnessed in breeding programs to develop drought-tolerant wheat varieties.