Purple Seed Stain Incidence Among Soybean Cultivars and Between Seasons in Puerto Rico

Abstract

Nine soybean cultivars (Buffalo, Cobb, Davis, Hardee Late Selection, IAC- 2, Improved Pelican, Jupiter, Orba, and Ransom) were planted at 11 dates from February 15, 1979 to October 1, 1979. At harvest maturity, the purple stained seeds from each of two 100-seed samples from each cultivar at each planting were counted. Variation in the incidence of purple seed was associated with cultivar and planting date. The highest overall incidences of purple seed were associated with Ransom (9.50%), Jupiter (8.27%); the lowest, in IAC-2 (0.29%), and Improved Pelican (0.23%). Precipitation and temperature levels were not associated with incidence of purple stain. Purple stain incidence was highly correlated with length of photoperiod at time of planting (r = -0.72); at 30 days after planting (r = - 0.97); and at 75 days after planting (r = -0.79). Shortened photoperiods appear to predispose soybean plants to purple stain. This fact may help explain the increased severity of purple stain in tropical areas compared with that in the temperate zones.