Bean rust biological control using bacterial agents

Abstract

Over 120 bacterial strains were evaluated in a greenhouse for control of bean rust caused by Uromyces appendiculatus. The strains, found previously to be antagonistic to some fungal pathogens, were isolated from dry edible bean ( Phaseolus vulgaris) and other hosts. Only Pantoea agglomerans B1, from a bean blossom, and Stenotrophomonas maltophilia C3, a chitinolytic strain from a Kentucky bluegrass leaf, were effective in multiple experiments in reducing bean rust severity. The addition of colloidal chitin to C3 cell suspensions and treatment with chitin broth cultures of C3 were evaluated as methods to improve biocontrol efficacy of C3. While chitin amendments increased rust control in the greenhouse as compared to C3 cells in buffer, chitin broth cultures gave the highest- and longest-lasting level of control. In four field experiments, treatments with C3 suspended in buffer, with and without chitin amendment, reduced rust severity in only one experiment. Strain B1 was not effective. In three other field experiments, C3 chitin broth cultures were comparable to multiple applications of thiophanate methyl or thiophanate methyl combined with manganese ethylenebisdithiocarbamate (maneb) in reducing bean rust severity.