Variation in mid-south soybean genotypes for recovery of transpiration rate and leaf maintenance following severe water-deficit stress

Abstract

Ninety-four percent of U.S. soybeans are produced under rainfed conditions with potential for intermittent late season droughts during reproductive stages. Therefore, the ability of a crop to recover effectively from drought is important for yield stability. In 2019 and 2020, two controlled environment and two field studies were conducted to screen nine soybean genotypes for transpiration rate (TR) recovery following water-deficit stress. In experiment 1, under a controlled environment, soybeans were grown in pots sealed to prevent evaporation. Soybeans gradually transpired until the endpoint of transpirable soil water before being re-watered. In experiment 2, soybeans were exposed to varying vapor pressure deficit (VPD) levels. In both experiments, TR was measured gravimetrically. In field studies, portable rainout shelters were used to exclude precipitation. In experiment 1 and the field studies, recovery irrigation was applied after a period of extreme water-deficit. Then, leaf wilting score (WS) was rated visually on a scale of zero to five. Stomatal conductance (g s ), pre- and post-recovery canopy temperature (CT), and stomatal density (SD) were measured under field conditions. Genotypic differences in soybean contributed to differentiated recovery from water-deficit in experiment 1 and field studies. In experiment 1, genotypes TN09–029, TN16–520R1, and Ellis had superior recovery from water-deficit based on WS while USG Allen and TN09–008 had the most rapid TR recovery; RIL #1360 and USG 7496XTS showed the least recovery. In experiment 2, seven genotypes expressed a limited-TR trait under high VPD. In the field studies, Ellis, USG Allen, and TN09–029 exhibited a more robust recovery based on WS and Ellis exhibited the highest post-recovery g s . TN09–029 and Ellis had the largest reduction in CT after recovery. The top five yielding genotypes all expressed desirable responses in several of the individual drought recovery traits, confirming the utility of these phenotypes. Ellis produced the highest yield at 3517 kg ha −1 , consistently expressed the early decrease in TR with delayed wilting when soil water-deficit developed, and had the highest g s post-recovery. Response and recovery to drought and high yield relative to other genotypes under the water-deficit conditions make Ellis and related lines good candidates in future efforts to breed for drought tolerance traits. • The ability of a crop to recover effectively from drought is important for yield stability. • Identifying variation in mid-south genotypes transpiration and leaf maintenance recovery from severe water-deficit stress. • Field studies confirmed the results found and reported in the controlled environment experiments. • The top yielding genotypes had early stomatal closure, lower stomatal density, and lower thermal rate following recovery.