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New Zealand Plant Protection 69 (2016): 48-56

Functional characteristics of New Zealand wheat rhizosphere Pseudomonas fluorescens isolates and their potential to inhibit in-vitro growth of Gaeumannomyces graminis var. tritici

R.M. Warren, S.F. Chng and R.C. Butler

ABSTRACT

Pseudomonas fluorescens are soil-inhabiting plant growth-promoting rhizobacteria (PGPR) linked with suppression of take-all of wheat, a soilborne disease caused by Gaeumannomyces graminis var. tritici (Ggt). PGPR increase plant growth by direct stimulation, producing metabolites (such as 2,4-diacetylphloroglucinol, 2,4-DAPG) to inhibit plant pathogens, or by inducing host defence mechanisms. Forty-three New Zealand P. fluorescens isolates collected from wheat rhizospheres of different cropping histories, were characterised for secondary metabolite production using biochemical assays and PCR analysis. Their ability to inhibit the growth of Ggt was determined in dual plate assays. All of the bacterial isolates produced siderophores, and 10 isolates produced hydrogen cyanide (HCN). However, none of the isolates produced indole acetic acid, and the phlD gene responsible for the production of 2,4-DAPG was not detected. Isolates that showed at least 60% inhibition of Ggt growth were found to produce either HCN or high levels of siderophore. The results suggest HCN and siderophores could play a role in suppressing Ggt and managing take-all in New Zealand.

Keywords: take-all decline, secondary metabolites, 2,4-DAPG, PhlD, disease suppression, hydrogen cyanide, indole acetic acid, PGPR.

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