Inhibitory Effect ofBacillus subtilisonUromyces phaseoliand on Development of Rust Pustules on Bean Leaves

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Abstract
Two isolates of B. subtilis and 1 isolate each of B. cereus (ssp. mycoides), B. thuringiensis and Erwinia ananas pv. uredovora were effective in controlling rust on beans under certain conditions. The most effective isolate was B. subtilis APPL-1. This isolate gave greater than 95% reduction in the subsequent number of rust pustules when it was applied in liquid culture to plants in the greenhouse 2-120 h prior to inoculation with U. phaseoli var. typica urediospores. The number of pustules was reduced on all tested bean cultivars, and with several different isolates of the fungus. When APPL-1 was applied after inoculation with urediospores, there was no effect on pustule number. Microscopic observations of B. subtilis-treated bean leaves showed urediospore germination was greatly reduced and no normal germ tubes were produced. Some urediospores developed abnormal cytoplasmic protrusions. An inhibitory component present in culture filtrates was nondialyzable and heat stable. Dialyzed culture filtrates were subjected to preparative gel filtration. The eluted material had an apparent MW of 5-10 kilodaltons, was inhibitory of U. phaseoli spore germination, and reduced bean rust severity. Analysis of the eluted fraction showed that it contained .apprx. 50% carbohydrate and 95% protein.

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