Genome-Wide Association Mapping Identifies QTLs for Yield Components under Heat Stress and Cold Tolerance during Seedling Establishment in Mung Bean (Vigna radiata)

Abstract Background. Heat stress during reproductive development and cold stress during seedling establishment are major constraints on mung bean ( Vigna radiata L. Wilczek) production. However, the quantitative trait loci (QTLs) underlying yield stability under heat stress and cold tolerance during seedling establishment remain largely unknown. A diversity panel comprising 126 mung bean accessions was evaluated for responses to heat and cold stress. Heat-stress responses were quantified as reductions in pod length and seed number per pod relative to control conditions. Cold tolerance during seedling establishment was assessed using germination rate, seedling vigor, and a visual chilling-injury score. Genome-wide association mapping was performed using the multi-locus FarmCPU model, stress-response phenotypes, and 710,906 high-quality single-nucleotide polymorphisms anchored to the JL7 reference genome. Allelic-effect analyses were subsequently conducted for each lead locus to distinguish robust QTLs associated with common alleles from potentially unreliable rare-allele associations. Results. QTLs associated with heat-stress responses and cold tolerance were located in distinct genomic regions. A major QTL controlling pod-length reduction under heat stress was identified on chromosome 3 and was consistently detected under two independent heat-stress regimes. This stable heat-tolerance QTL was associated with a common allele that had a large phenotypic effect. Two stable QTLs associated with common alleles were identified for cold tolerance during seedling establishment: one for seedling vigor under cold stress on chromosome 7 at 2.69 Mb and another for chilling-injury score on chromosome 6 at 19.87 Mb. These QTL regions contained biologically plausible candidate genes, including a gene encoding an FKBP62-type immunophilin co-chaperone within the chromosome 3 heat-tolerance QTL and genes encoding the CBF/DREB1 regulator CAMTA5 and a DnaJ/Hsp40 co-chaperone within the chromosome 7 cold-tolerance QTL. Conclusions. Genome-wide association mapping combined with allelic-effect validation identified stable QTLs associated with yield components under heat stress and cold tolerance during seedling establishment in mung bean. The heat- and cold-tolerance QTLs were genomically independent, indicating that pyramiding distinct loci will be necessary to combine tolerance to both stresses. These QTLs, particularly those associated with common alleles, represent promising targets for marker-assisted breeding of climate-resilient mung bean cultivars.