VIEW ARTICLE

Ecology and Epidemiology

Production of Ammonia by Enterobacter cloacae and Its Possible Role in the Biological Control of Pythium Preemergence Damping-off by the Bacterium. C. R. Howell, Research plant pathologist, Agricultural Research Service, U. S. Department of Agriculture, Southern Crops Research Laboratory, P. O. Drawer JF, College Station, TX 77841; R. C. Beier(2), and R. D. Stipanovic(3). (2)Research chemist, Agricultural Research Service, U. S. Department of Agriculture, Veterinary Toxicology and Entomology Research Laboratory, P. O. Drawer GE, College Station, TX 77841; (3)Research chemist, Agricultural Research Service, U. S. Department of Agriculture, Southern Crops Research Laboratory, P. O. Drawer JF, College Station, TX 77841. Phytopathology 78:1075-1078. Accepted for publication 7 March 1988. 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, 1988. DOI: 10.1094/Phyto-78-1075.

Strains of Enterobacter cloacae reported to be biological control agents of seedling and postharvest diseases were found to symmetrically inhibit fungal growth when grown in dual cultures. Inhibition of fungal growth by E. cloacae in partitioned plates indicated that the inhibitor was volatile. Distillation and low-temperature trapping of released volatiles resulted in the capture of an antifungal compound that was identified as ammonia by mass spectroscopy. Assay of ammonia for activity against Pythium ultimum and Rhizoctonia solani showed that both were inhibited at low concentration and that the former was more sensitive than the latter. The addition of some sugars (d-galactose, d-glucose, sucrose, and β -methyl-d-glucoside) suppressed the production of ammonia by E. cloacae when added to the growth medium. Other sugars (3-O-methyl-d-glucose, d-trehalose, and l-sorbose) did not inhibit ammonia production. In a previous study, the sugars in the former group interfered with biocontrol activity, and the sugars in the latter group did not. These results indicate that ammonia production by E. cloacae may be the fungal growth-inhibiting part of the mechanism by which E. cloacae controls Pythium preemergence damping-off.