Physiological drought responses and recovery in Mexican soybean genotypes: Implications for sustainable water management.

Drought is a major abiotic constraint on soybean productivity and an increasing challenge for agricultural sustainability under water-limited conditions. Understanding plant responses to drought is essential for identifying traits associated with crop adaptation and resilience. This study evaluated the physiological responses of three Mexican soybean genotypes (E2309, I1240, and I700) to 17 days of progressive drought during the reproductive stage, followed by an 8-day recovery period after re-watering. Control plants remained well-watered throughout the experiment. Canopy wilting, stomatal conductance, transpiration, and leaf and pod production were the most drought-sensitive traits and showed only partial recovery, whereas instantaneous water use efficiency increased during moderate drought and remained elevated under severe stress. Genotype E2309 showed increased instantaneous water use efficiency under moderate drought and higher GmZEP gene expression under severe stress, whereas genotypes I1240 and I700 showed lower canopy wilting and lower GmPIP2-5 gene expression under severe drought. Genotype I700 exhibited the most favorable combination of photosynthetic pigment concentrations and instantaneous water use efficiency under drought, together with recovery of leaf and pod production. These findings highlight substantial genotypic variation in drought and recovery responses and identify genotype I700 as a promising genetic resource for further evaluation in soybean improvement under water-limited environments. Canopy wilting, instantaneous water use efficiency, and photosynthetic pigment stability may provide practical indicators for identifying genotypes with favorable drought-response and recovery characteristics. The molecular findings should be considered exploratory and require further validation using additional drought-responsive genes and functional approaches.