A PHYSIOLOGICALLY-INDUCED RESISTANCE OF PHASEOLUS-VULGARIS TO A COMPATIBLE RACE OF COLLETOTRICHUM-LINDEMUTHIANUM IS ASSOCIATED WITH INCREASES IN ABA CONTENT

Isolated hypocotyls from Phaseolus vulgaris seedlings to which different organs were left attached differed in their resistance to a compatible race of the fungal pathogen Colletotrichum lindemuthianum. Hypocotyls which retained cotyledons or leaves were more resistant than those which lacked these organs. The degree of resistance, assessed 10 days after inoculation, was related to the concentration of abscisic acid (ABA) in hypocotyls 4 days after inoculation, when the pathogen was in its progressive biotrophic phase. Symptom severity decreased following application of ABA to susceptible hypocotyls. Application of fluridone, an inhibitor of ABA biosynthesis, to resistant hypocotyls increased symptom severity. ABA had no direct effect on pathogen growth. The results suggest that the resistance induced by retention of leaves and/or cotyledons results from ABA-induced changes in host cell physiology leading to a reduction in the extent of the pathogen's biotrophic growth. © 1990.