EFFECT OF PLANT-GROWTH REGULATORS ON THE INTERACTIONS BETWEEN BEAN-PLANTS AND RUST FUNGI NONPATHOGENIC ON BEANS

Abscisic acid and gibberellic acid, when injected into bean leaves, reduced the incidence of silica deposition and autofluorescent materials on mesophyll walls at infection sites and increased the incidence of haustoria produced by the normally incompatible cowpea rust fungus. A similar effect was also observed for the corn rust fungus, except that the incidence of autofluorescent walls was not reduced, probably because of the increased autofluorescence of the contents of invaded cells. Indole-3-acetic acid at 2 × 10-4 M slightly increased haustorium formation by the cowpea or corn rust fungi without affecting the incidence of silica deposition or autofluorescent walls. No concentration of kinetin had any effect on the interactions between bean leaves and the three rust fungi tested. None of the growth regulators had any observable effect on the sunflower rust-bean interaction. Abscisic acid, gibberellic acid, or indole-acetic acid did not induce in vitro haustorium formation on collodion membranes by either the cowpea or the corn rust fungus, suggesting that the effect of the growth regulators may not be the result of direct induction of haustorium formation. The results of this study support the conclusion from previous studies that there are significant differences in the ways different rust fungi interact with the same non-host plant. The data also suggest that abscisic acid and gibberellic acid increase tissue susceptibility to rust fungi in a different manner from the intercellular washing fluids from rusted bean leaves studied previously. © 1990.