Date of Award
5-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Plant and Environmental Science
Committee Chair/Advisor
Sandra Branham
Committee Member
Patrick Wechter
Committee Member
Elizabeth Cieniewicz
Committee Member
Richard Boyles
Abstract
Snap bean (Phaseolus vulgaris L.) is an economically and nutritionally important vegetable crop whose production is increasingly threatened by rising temperatures and emerging bacterial diseases, particularly in the southeastern United States. Heat stress during reproductive development can significantly reduce yield, while newly emerging pathogens such as Pseudomonas capsici present additional risks to crop productivity. This study leveraged the USDA Snap Bean Association Panel (SnAP) to investigate the genetic basis of heat tolerance and disease resistance and to identify germplasm and genomic regions useful for breeding resilient cultivars.
To evaluate heat tolerance, a subset of the SnAP panel was assessed in replicated field trials conducted across spring, summer, and fall growing seasons in Charleston, South Carolina. These trials were designed to capture both optimal and heat-stress environments. Yield-related traits, including total yield, marketable yield, and pod characteristics, were measured. Heat stress during summer production resulted in substantial reductions in yield, consistent with known effects of elevated temperatures on reproductive development. However, several accessions maintained significantly higher productivity under heat stress, demonstrating the presence of exploitable genetic variation for heat tolerance within cultivated snap bean germplasm.
To investigate the genetic architecture underlying heat tolerance, genome-wide association studies (GWAS) were conducted using genotyping-by-sequencing data comprising approximately 28,000 single nucleotide polymorphisms (SNPs). The analysis identified 15 significant SNPs associated with traits related to yield under heat stress, including pod number and pod weight. These loci were distributed across multiple genomic regions, indicating that heat tolerance is a quantitatively inherited, polygenic trait. Candidate gene analysis revealed several genes associated with stress response pathways, including heat shock proteins, which play critical roles in protein stabilization and cellular protection under elevated temperatures.
In parallel, resistance to bacterial leaf spot caused by Pseudomonas capsici, an emerging pathogen of concern in vegetable production systems, was evaluated using a greenhouse-based inoculation assay. A total of 380 accessions from the SnAP panel were screened, and disease severity was quantified using digital image analysis. Substantial phenotypic variation was observed, with disease severity ranging from minimal to complete susceptibility. Broad-sense heritability was moderate (H² = 0.41), indicating a significant genetic component to resistance. Genome-wide association analysis identified significant marker–trait associations on chromosomes 5 and 6, with the most consistent signals located on chromosome 6. Candidate genes within these regions were associated with plant immune and defense-related pathways, suggesting a complex genetic basis for resistance.
Collectively, these results demonstrate that both heat tolerance and resistance to P. capsici in snap bean are controlled by multiple loci and are influenced by complex genetic architectures. The identification of superior-performing accessions under stress conditions, along with associated genomic regions, provides valuable resources for marker-assisted selection and genomic-assisted breeding. This work highlights the utility of integrating multi-environment phenotyping with high-density genotyping to accelerate the development of climate-resilient and disease-resistant snap bean cultivars. Ultimately, these findings contribute to improving the sustainability and productivity of snap bean production systems under increasing environmental and biotic stress pressures.
Recommended Citation
Khan, Atiya F., "Mining the USDA Snap Bean Association Panel for Resilience: Genetic Dissection of Heat and Disease Tolerance in Snap Bean" (2026). All Theses. 4720.
https://open.clemson.edu/all_theses/4720