Effect of sowing date on the growth and seed yield of common bean (Phaseolus vulgaris L.) in highland environments

Evaluations of common bean cultivars in the highlands of Mexico indicated that land races from that region experience less reduction in seed yield and seed size in late sowings than do lines from other regions. Introduced materials are of interest as sources of increased disease and pest resistance and tolerance to edaphic constraints, however. To quantify effects of sowing date and determine possible underlying causes, germplasm of diverse origins was evaluated at two sites in the highlands using multiple sowing dates. In all trials, seed yield, seed weight, harvest index and canopy dry weight decreased with late sowings. Large effects of sowing date, cultivar and their interaction were found for the four traits. The possible importance of phenology per se and of weather conditions was first examined using regression analyses. Variation in seed yield, seed weight, harvest index and canopy dry weight was more closely associated with time to maturity than with time to flowering. Of three weather variables examined, minimum temperature during seed filling revealed the strongest relations with the four traits. Few interactions of any parameter with line were significant, indicating that the cultivars did not have a strong differential response to a specific weather condition such as night temperature. Simulation analyses comparing photoperiod-sensitive and day-neutral cultivars indicated that radiation and temperature explained part of the yield reduction with late sowings. Daylength also had an influence, however, even in the day-neutral cultivar. Given that phenology had a strong effect on yield and that its inheritance is better understood than that of other physiological traits, priority should be given to understanding the genetic basis of the response of cultivar phenology to sowing date in the region.