VIEW ARTICLE

Ecology and Epidemiology

Inhibitory Effect of Bacillus subtilis on Uromyces phaseoli and on Development of Rust Pustules on Bean Leaves. C. Jacyn Baker, Research plant pathologists, Plant Pathology Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; J. R. Stavely(2), C. A. Thomas(3), Myron Sasser(4), and Janet S. MacFall(5). (2)(3)Research plant pathologists, Plant Pathology Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD 20705; (4)(5)Professor and research associate, respectively, Department of Plant Sciences, University of Delaware, Newark 19711. Phytopathology 73:1148-1152. Accepted for publication 14 March 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-1148.

Two isolates of Bacillus subtilis and one isolate each of B. cereus (subsp. 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 to 120 hr 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 molecular weight of 5 to 10 Kdaltons, was inhibitory to U. phaseoli spore germination, and reduced bean rust severity. Analysis of the eluted fraction showed that it contained approximately 5% carbohydrate and 95% protein.