Responses of common bean (Phaseolus vulgaris L.) to photosynthetic irradiance levels during three phenological phases

As a dominant component crop in intercropping systems, common bean is exposed to radiation deficit during various phases. An indeterminate cultivar was examined from twenty-seven treatments consisting of all possible combinations of three levels of photosynthetic irradiance, 100, 250 and 400 μmol m -2 s -1 , applied during three phenological phases. Acclimation characteristics to reduced irradiance included lower chlorophyll a/b ratio, reduced stomatal density, increased specific leaf area and leaf area ratio and increased shoot-root ratio. Susceptibility of the phases varied when comparisons were made based on entire phases and a magnitude that considered timing and light interception. Number of pods per plant, the predominant yield component, responded to irradiance level during all phases but most during flowering. For number of seeds per pod the only relevant phase was seed filling while seed weight responded during flowering and seed filling. A significant interaction between the irradiance levels of phases was observed for pod number.