Relationship Between In Vitro Inhibition ofGaeumannomyces graminisvar.triticiand Suppression of Take-All of Wheat by Fluorescent Pseudomonads

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Abstract
Fluorescent Pseudomonas spp. isolated from roots of wheat that had been grown in a take-all suppressive soil were more inhibitory to Gaeumannomyces graninis 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 conductive (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. Rla-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. There 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.