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Disease Control and Pest Management

Control of Rhizoctonia solani on Cotton Seedlings with Pseudomonas fluorescens and With an Antibiotic Produced by the Bacterium. C. R. Howell, Research plant pathologist, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, National Cotton Pathology Research Laboratory, P.O. Drawer JF, College Station, TX 77840; R. D. Stipanovic, research chemist, U.S. Department of Agriculture, Science and Education Administration, Agricultural Research, National Cotton Pathology Research Laboratory, P.O. Drawer JF, College Station, TX 77840. Phytopathology 69:480-482. Accepted for publication 15 November 1978. 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, 1979. DOI: 10.1094/Phyto-69-480.

A strain of Pseudomonas fluorescens antagonistic to Rhizoctonia solani was isolated from the rhizosphere of cotton seedlings. An antibiotic strongly inhibitory to R. solani was isolated from P. fluorescens cultures and identified as pyrrolnitrin (3-chloro-4-[2-nitro-3-chlorophenyl]-pyrrole). The antibiotic also inhibited growth of other fungi associated with the cotton seedling disease complex including: Thielaviopsis basicola, Alternaria sp., and Verticillium dahliae. A Fusarium sp. was only partially inhibited and Pythium ultimum was unaffected. Treating cottonseed with P. fluorescens or pyrrolnitrin at time of planting in R. solani-infested soil increased seedling survival from 30 to 79% and from 13 to 70%, respectively. Pyrrolnitrin persisted for up to 30 days in moist nonsterile soil with no measurable loss in activity.

Additional keywords: seed treatment, biological control.