Updated January 31, 2022:
Drought conditions in the United States are estimated to result in average annual losses in the range of $10 to $14 billion. Identification of genetic mechanisms for tolerating periods of drought is critical to sustaining crop production and yield. Therefore, over 1000 de-rooted shoots of 150 upper mid-south soybean lines were tested using silver nitrate to determine the expression of the limited transpiration (TRlim) trait (i.e., slow wilting) among soybean lines under high evaporative demand (> 2.5 kPa). Among 122 lines, half of the population showed higher sensitivity (fast wilting) to silver nitrate than their parents. However, several lines showed no or limited changes in water loss (slow wilting) with the silver treatment. Therefore, after the silver treatment 26 lines out of 122 were selected for measuring the whole plant transpiration rate under dry air (i.e., high evaporative demand) in a walk-in growth chamber. All 26 lines were divided into 3 categories: 1) slow, 2) moderate, and 3) fast wilting based on silver test results. The whole plant transpiration results indicated that 71% of category 1, 40% of category 2, and 33% of category 3 soybean lines expressed limited water loss which shows water saving potential under dry air in a controlled environment. The lowest transpiration rate (and presumably most water saving) lines had a combination of Quantitative Trait Locus (QTL) from two different parents (Chr10, Jackson; Chr12, KS2495). Lines which inherited alleles from KS4895 for the Chr12 QTL for Canopy temperature (which was genetically distinct from the TR QTL) had lower canopy temperatures (0.84 °C on average across all RILs). Moreover, the soybean lines that showed limited water loss during whole plant transpiration test in contolled environemnts were studied under field conditions in 2020. A correlation was found between water use efficiency intrinsic (WUEk) and lower stomatal conductance. Soybean lines that showed higher water use efficiency (WUEk) also had lower stomatal conductance. In average genotypes with expressing the TRlim/Drought tolerant trait (i.e., RILs #91, #22, #151, and #93) had 20-22% higher yield than other soybean genotypes (2020-2021).