Water relations, histopathology and growth of common bean (Phaseolus vulgaris L.) during pathogenesis of Macrophomina phaseolina under drought stress

Alterations in water relations, growth and histopathology caused by Macrophomina phaseolina, causal agent of charcoal rot, and drought stress were characterized in Phaseolus vulgaris L. under controlled conditions. P. vulgaris cultivars BAT 477 and TLP 19 (resistant) and Pinto UI-114 and Rio Tibagi (susceptible) were cultivated under irrigation and drought stress conditions in infested or uninfested pots with a highly virulent isolate of M. phaseolina. Drought stress showed higher negative effects than AT phaseolina on water relations, vegetative growth and histopathology in P. vulgaris. Drought stress decreased transpiration rate, water potential, osmotic potential, turgor potential, relative water content, leaf area and dry weight of all vegetative structures of P. vulgaris. Drought stress increased charcoal rot development and stomatal resistance, and increased the association among physiological and growth characteristics and charcoal rot development. If. phaseolina invaded between epidermal cells of BAT 477 and Pinto UI-114 hypocotyls. The fungus infected cortex tissues, vascular cylinder, and pith cells of Pinto UI-114, but only epidermal and parenchyma cells of BAT 477. Typical symptoms caused by M. phaseolina were found to be associated with damage caused by the fungus on host tissues, and they were related to drought stress. (C) 2002 Elsevier Science Ltd. All rights reserved.