Genomic resources to advance seed coat color and patterning genetics and breeding in common bean (Phaseolus vulgaris L.).

Abstract

Seed coat color and patterning are key quality traits in common bean (Phaseolus vulgaris L.) that define market classes and strongly influence consumer preference and market value. These traits are controlled by a complex network of major genes (sometimes with epistatic interactions), which complicates the recovery of desired market class phenotypes following inter-market class hybridization. Although many of the underlying loci have been genetically mapped, diagnostic, high-throughput molecular markers for efficient allele tracking across the Middle American and Andean gene pools remain limited. In this study, we developed and validated 24 gene-specific PCR Allele Competitive Extension (PACE) markers targeting seven major seed coat color genes (G, B, V, J, Rk, T, and Z) and two patterning genes (C^Pi and C^St), together with a previously reported marker associated with the postharvest seed coat darkening locus (P^sd). An additional PACE marker targeting the Phaseolin (Phs) locus was developed to distinguish Middle American (S-type) and Andean (T-type) gene pools, providing a complementary tool for assessing genetic background alongside seed coat-specific loci. Marker performance was evaluated across three diverse panels, revealing high diagnostic accuracy for most loci (90%-100%). However, for loci such as J, V, Rk, T, and Z, allele-specific markers or marker combinations were required to capture full allelic diversity. Haplotype analysis further revealed substantial allelic diversity across market classes and identified background-specific interactions. Collectively, these results provide a comprehensive set of high-resolution, gene-anchored PACE markers for seed coat color, patterning, and gene pool classification in common bean. These markers enable rapid and precise allele tracking in breeding populations and germplasm collections, facilitating marker-assisted selection for market class-specific seed coat traits and accelerating genetic improvement.