High-throughput phenotyping of soybean (Glycine max) transpiration response curves to rising atmospheric drying in a mapping population

In soybean (Glycine max ), limiting whole-plant transpiration rate (TR) response to increasing vapor pressure deficit (VPD) has been associated with the 'slow-wilting' phenotype and with water-conservation enabling higher yields under terminal drought. Despite the promise of this trait, it is still unknown whether it has a genetic basis in soybean, a challenge limiting the prospects of breeding climate-resilient varieties. Here, we present the results of a first attempt at a high-throughput phenotyping of TR and stomatal conductance response curves to increasing VPD conducted on a soybean mapping population consisting of 140 recombinant inbred lines (RIL). This effort was conducted over two consecutive years, using a controlled-environment, gravimetric phenotyping platform that enabled characterizing 900 plants for these responses, yielding regression parameters (R 2 from 0.92 to 0.99) that were used for genetic mapping. Several quantitative trait loci (QTL) were identified for these parameters on chromosomes (Ch) 4, 6, and 10, including a VPD-conditional QTL on Ch 4 and a 'constitutive' QTL controlling all parameters on Ch 6. This study demonstrated for the first time that canopy water use in response to rising VPD has a genetic basis in soybean, opening novel avenues for identifying alleles enabling water conservation under current and future climate scenarios.