Importance of biotic pollination varies across common bean cultivars

Abstract

Common bean (Phaseolus vulgaris L.) flowers are morphologically adapted to biotic pollination, although it is partially autogamous. We evaluated the effect of pollinator visits on pod and seed production of 14 local creole cultivars of P. vulgaris, commonly used in organic farming. We collected descriptive data observing the flower visitors and estimating the number and viability of pollen grains, flower size, nectar volume and nectar sugar concentration. Overall, exposure to flower visitors (legitimate pollinators and robbers) improved production in terms of quantity or quality of pods and/or seeds of eight cultivars and reduced production of two other cultivars. We found 10 insect species visiting flowers of the bean cultivars, but only Xylocopa bees behaved as legitimate pollinators. Other flower visitor species either pierced the corolla base to get the nectar or got the nectar without lowering the flower's wings and keels to touch anthers and stigma. Petal length and nectar features showed few variations among the cultivars. Two cultivars produced a larger amount of pollen grains than the remaining cultivars. Despite some variation across cultivars, our results suggest the importance of native bees to pollination and reproductive success of creole beans.