EFFECTS OF SEED SIZE AND PHOTOPERIOD RESPONSE ON CROP GROWTH AND YIELD OF COMMON BEAN

Seed size and yield are usually negatively associated among common bean (Phaseolus vulgaris L.) cultivars of bush growth habit. Furthermore, among cultivars varying in photoperiod response for flowering, yields are often lower in photoperiod-sensitive genotypes. While the seed-size effect might extend to overall crop growth, photoperiod response would be expected primarily to influence phenology and, possibly, partitioning. To examine these hypothesized effects, yield, crop dry weight at two stages, harvest index (HI), and day to maturity were evaluated for 62 genotypes grown at three sites in Colombia and at Davis, California. Regression analyses indicated highly significant negative relationships between seed weight and all variables except days to maturity, even when significant photoperiod effects were accounted for or when analyses were restricted to genotypes from highland environments. Greater sensitivity to photoperiod was associated with lower yields and HI, and delayed maturity, at Davis, and there was a similar, but much weaker, trend of lower yield and HI in the other environments. Because large seed size was associated with reduced growth, relative growth rate (RGR) of 16 bean genotypes was measured at two of the Colombian sites. At both sites, RGR was negatively correlated with seed weight (R2 = 0.59 and R2 = 0.44, P < 0.01). These results suggest that greater seed size is associated not only with reduced yield, but also with reduced overall growth, and that the effect is largely independent of photoperiod sensitivity, even though the latter influenced phenology and partitioning.