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Ecology and Epidemiology

Relationship Between In Vitro Inhibition of Gaeumannomyces graminis var. tritici and Suppression of Take-All of Wheat by Fluorescent Pseudomonads. David M. Weller, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture; William J. Howie(2), and R. James Cook(3). (2)Graduate research assistant, Department of Plant Pathology, Washington State University, Pullman, WA 99164-6430, Research scientist, Advanced Genetic Sciences, Oakland, CA 94608; (3)Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Pullman, WA 99164-6430. Phytopathology 78:1094-1100. Accepted for publication 21 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-78-1094.

Fluorescent Pseudomonas spp. isolated from roots of wheat that had been grown in a take-all suppressive soil were more inhibitory to Gaeumannomyces graminis var. tritici in vitro and more suppressive to take-all as seed treatments than fluorescent pseudomonads isolated from roots that had been grown in a take-all conducive (nonsuppressive) soil. The relationship between the ability of fluorescent pseudomonads to inhibit G. g. tritici in vitro and suppress take-all of wheat in soil was then examined. Pseudomonas fluorescens strains 2-79RN₁₀. R1a-80R, and R7z-80R were treated with N-methyl-N’-nitro-N-nitrosoguanidine, and mutants were selected that lost or were reduced in the ability to produce antibiotics and/or siderophores in vitro. These mutants also lost some or all of their ability to suppress take-all but still colonized wheat roots to the same degree as their respective parents. The addition to the soil of excess Fe(III) in the form of ferric-ethylenediamine-tetraacetic (FeEDTA) acid to repress siderophore production eliminated suppression of take-all by Pseudomonas putida L30b-80, reduced suppression by strain 2-79, and had no effect on strain R1a-80. The results confirm previous conclusions that fluorescent pseudomonads have a role in take-all decline and that suppression of take-all by some fluorescent pseudomonads is mediated in part by production of antibiotics and/or siderophores.