Foliar response of wild and domesticated Phaseolus vulgaris L. to water stress

It is surmised that domestication has reduced genetic variability in the common bean (Phaseolus vulgaris L.). However, little is known about leaf anatomy responses to water stress in wild or domesticated forms of P. vulgaris. In this study, anatomical variation was evaluated in watered and water stressed plants of wild and domesticated genotypes of P. vulgaris from Mexico, growing under greenhouse conditions. Five terminal leaflets of completely expanded leaves were used to evaluate leaf area (LA)and their middle-regions to evaluate leaf thickness (LT), and various anatomical features. Domesticated genotypes showed bigger LA than that of the wild ones; there was an effect due to the origin of materials, LA being bigger in genotypes from warm and humid lands that those from dry and temperate ones. No differences were detected in LT among materials; however, in domesticated plants the palisade parenchyma predominated over the spongy one, contrasting with the wild genotypes. Under drought conditions, stomatal abortion was observed in wild and domesticated genotypes, especially on the abaxial surface. We conclude that, in fact, there are contrasting differences in leaf anatomy among wild and domesticated forms of Mexican Phaseolus vulgaris. Results suggest that domestication not only favours the enlargement of the LA, but also an increase in palisade parenchyma, suggesting a divergence toward assimilation in domesticated forms, in contrast with a better internal gas diffusion in wild forms. Domestication seems to have accentuated stomatal abortion as means of a transpirational control mechanism to counteract the effects of drought.