Variation in leaf movements among common bean cultivars

Common beans (Phaseolus vulgaris L.) orient their leaves in response to directionality of the sun's direct beam. This study was initiated to test for genetic variability in leaflet orientation, especially variability related to geographic origin. We also determined genetic variability in diurnal, seasonal, and environmental influences on leaflet orientation. The studies included 75 Mesoamerican and Andean common bean lines and two tepary bean (Phaseolus acutifolius Gray) lines at two sites. Cos i (cosine of the angle of incidence to direct sunlight) varied in the order tepary bean> Andean common bean> Mesoamerican common bean. Within sites, variability in seasonal and year-to-year patterns of leaf movement was significant, but there were large differences in rankings of lines across sites. Imposed drought decreased cos i, but values of cos i in drought and irrigated treatments remained correlated. Movements of the two lateral leaflets were highly correlated with each other for most of the day, but within many common bean lines were not related to the movements of the terminal leaflet. Thus, at the canopy level the overall impact of the pronounced movements of the terminal leaflet were diminished by movements of the lateral leaflets. The results show substantial genetic variability in both short-term and long-term leaflet movements in beans, some of which is related to geographic origin eng