Genome-wide association study of water use patterns of common bean (Phaseolus vulgaris L.) genotypes in response to drying soil

Common bean (Phaseolus vulgaris L.) is the main legume crop for direct human consumption worldwide, especially in developing countries. Among the abiotic factors affecting common bean production, drought is the most limiting condition. Capacity for the accurate identification and selection of drought-tolerant genotypes is a paramount step in the improvement of new cultivars. This study is aimed at characterizing the genetic variability and genetic architecture of transpiration, stomatal regulation and whole plant water use within the Mesoamerican common bean germplasm. Three greenhouse experiments were conducted, and water use was recorded gravimetrically. Transpiration of water-stressed plants was normalized against well-watered plants to obtain a normalized transpiration rate (NTR). A critical fraction of transpirable soil water (FTSWc) was estimated as the inflection point at which NTR starts decreasing linearly. Genome-wide association (GWA) analyses for average NTR and FTSWc were performed. High variation in average NTR and FTSWc was found among genotypes. Genomic signals (QTL) controlling the variation of these traits were identified on Pv01 and Pv07 some located in intergenic, intronic and exonic regions. A set of novel candidate genes and putative regulatory elements located in these QTL were identified. Most of the genes have been previously reported to be involved in abiotic tolerance, including some of the five transcription factors identified. Candidate genes can be used for marker-assisted selection and further study of drought tolerance mechanisms in common bean. Our results provide tools to accelerate the drought tolerance improvement in the crop.