Developing Strategies to Improve Dry Bean Tolerance to Waterlogging Stress.

Current trends of climate change suggest the occurrence of more frequent flooding incidents in poorly-drained agricultural land. This stress significantly reduces crop production mainly due to exposing plants to hypoxia. Dry bean (Phaseolus vulgaris L.) is the most important grain legume worldwide but it is also one of the most sensitive crops to flooding, causing ~15% yield losses in North Dakota and Minnesota. To reveal the genetic architecture of waterlogging tolerance in dry bean, ~500 genotypes were evaluated at germination and seedling stages under greenhouse conditions. We employed a RCBD with a split plot arrangement. Seven traits were evaluated including germination rate, total weight, shoot weight, root weight, hypocotyl length, chlorophyll content, and adventitious root formation. Lines were genotyped using ~150K SNP markers. The results indicate that Middle-American and Andean gene pools use quiescence and escape strategies, respectively, to cope with waterlogging stress. Different market classes respond differently to excess water for all traits except hypocotyl length. For root weight, which was the trait, most affected by waterlogging, pinto and great northern were the most tolerant market classes. Chlorophyll content reduction was more pronounced in navy and black market classes (48% and 34% reduction, respectively) in comparison to pinto and great northern (16% reduction). Germination rate of black beans was the least affected (63% reduction) by the excess water; contrastingly, navy beans (84% reduction) were the most susceptible. To detect the potential causative loci that confer tolerance, we employed a Genome-Wide Association Study (GWAS). Among the more than 30 loci detected, two major regions were on Pv08/1.6 and Pv02/41.1 controlling root weight and germination rates, respectively. Interestingly, these loci are in synteny with waterlogging QTL reported in soybean, indicating potential conserved evolutionary mechanisms. These loci are beneficial to develop an effective strategy to improve dry bean tolerance to waterlogging stress.