An accelerated postharvest seed-coat darkening protocol for pinto beans grown across different environments

Pinto beans (Phaseolus vulgaris L.) that darken more slowly than conventional pinto beans would be more desirable in the market place and have been identified in the bean breeding program at the University of Saskatchewan. To incorporate the slow-darkening trait into new cultivars there is a need for a quick, reliable, and inexpensive method to accelerate darkening without affecting seed germination. Three different accelerated darkening protocols were compared. The greenhouse protocol was conducted in the greenhouse by placing the bean seeds in plastic bags with a 1-cm(2) piece of moistened felt. For the ultraviolet C (UVC) light protocol, bean seeds were placed 10 cm below a 254-nm UVC lamp. For the third protocol, bean seeds were placed in a cabinet set at 30 degrees C, 80% relative humidity, and full fluorescent light. All three protocols examined could be used to distinguish darkening beans from slow-darkening beans, however. the UVC protocol was considered superior as it was quick, consistent over years, and economical and, unlike the greenhouse and the cabinet protocols, had no effect on seed germination. A genotype by environment (g x e) study was conducted to validate the UVC light protocol. After accelerated darkening, line and environment effects were found to be significant (P < 0.0001) but the g x e interaction was not significant (P = 0.29), which indicated that the UVC protocol could be used to distinguish slow-darkening pinto beans from darkening pinto beans, regardless of where the beans were grown.