Differences in growth and water relations among Phaseolus vulgaris cultivars in response to induced drought stress

Relatively little ecophysiological research has been conducted to determine the responses to drought of Phaseolus vulgaris. Four bean cultivars (cvs.) from Brazil, A320, Carioca, Ouro Negro and Xodo were submitted to an impos ed water deficit in order to evaluate the importance of some adaptive mecha nisms of drought resistance through the analysis of growth parameters, wate r status, gas exchange and indicators of tolerance mechanisms at the cellul ar level. During the drought treatment, relative growth rates were more red uced for A320 and Xodo than Carioca and Ouro Negro. A320 closed its stomata very rapidly and complete stomatal closure eras obtained at Psi(w) = - 0.6 MPa, in contrast to the other cvs. where stomata were fully closed only at Psi(w) = - 0.9 MPa. Net assimilation rates were closely related to stomata l conductances. Mechanisms at the cellular level appeased to be mostly impo rtant for higher tolerance. Carioca and Ouro Negro, when compared to A320 a nd Xodo, were characterized by having better drought tolerance mechanisms a nd higher tissue water retention capacity leading to a better growth under water deficits. The leaf dehydration rates of those cvs. were slow whereas those of the drought sensitive cvs. were rapid. The results were confirmed by the electrolyte leakage test and leaf osmotic potential measurements, wh ich indicated higher membrane resistance and osmotic adjustment in the two tolerant cvs. Carioca and Ouro Negro. It appears from this study that despi te being cultivated in the same geographical region, the four cvs. of P. vu lgaris displayed somewhat different drought adaptive capacities for prolong ed drought during the vegetative phase. (C) 2000 Elsevier Science B.V. All rights reserved.