Slow darkening in pinto bean (Phaseolus vulgaris L.) seed coats is controlled by a single major gene

Postharvest seed coat darkening is a significant problem in pinto beans (Phaseolus vulgaris L.), resulting in product that is undesirable to consumers and that is discounted in the marketplace. There is a range in the rate and extent of darkening among pinto germplasm and recently, slow-darkening (SD) lines have been identified. Line 1533-15, an SD line from the University of Saskatchewan, was crossed to CDC Pintium, a regular darkening pinto, and seed of F-1 and F-2 individuals and F-5:6 recombinant inbred lines were assessed for their darkening phenotype. Segregation data indicated that there is a single, recessive gene that controls the SD phenotype. All F-2 individuals from a cross between 1533-15 and Pinto Saltillo, another SD line, were slow-darkening suggesting that the phenotype is controlled by the same gene in both lines. The simple genetics of this trait should facilitate the introduction of this trait into breeding programs, thereby increasing the quality of pinto beans being developed.