DARKENING OF THE SEED COAT IN DRY BEAN GENOTYPES DURING EARLY DAYS AFTER HARVEST

INTRODUCTION As it is a center of origin of dry beans (Phaseolus vulgaris L.), in Mexico there are a wide variety of colors and shapes that are consumed. Post harvest, darkening of the seed coat is a problem in light colored beans, which decreases its marketability. In the lab, coat color is evaluated by reflectance spectrophotometry and it is used as a parameter for selection in genetic improvement. Although this trait exhibits a clear genotype-environment interaction, it is possible to select genotypes with greater color stability during storage, which is associated with increased in shelf life. In previous studies (Jacinto et al. 2006, 2007) polyphenol oxidase activity has been associated with the proneness of genotypes to darkening during storage. To select genotypes less prone to darkening of seed coat, accelerated aging is induced in the beans by increasing the temperature and relative humidity, this process implies time and work. The objective of this study was to assess the tendency of a group of eleven genotypes to darken during the first 44 days after harvesting. MATERIALS AND METHODS During PV 2014, eleven dry bean genotypes were sown at Santa Lucía de Prías, Texcoco, estado de México. The experimental plot was one 4 m- long row. Except for one black seed coat variety, the other 10 genotypes were light colored either with pattern or one single color. Upon reaching maturity, the plants of each plot were hand threshed. The first day after threshing color was measured using a CM-5 spectrophotometer (Konica Minolta, Inc., Osaka, Japan). Color reflectance was recorded in the CIE Lab color coordinate system, with D65 Illuminant and 10º observer. Samples were then left at room temperature in glass cases for 44 days. During 28 days color measurements every two to three days were taken; then it was measured at 44 days. Data was processed through an analysis of variance and a correlation test