|Yang, Ming Ming|
|Guo, Jian Hua|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2011
Publication Date: 12/1/2011
Citation: Yang, M., Mavrodi, D.V., Mavrodi, O.V., Bonsall, R.F., Pareko, J.A., Paulitz, T.C., Thomashow, L.S., Hetong, Y., Weller, D.M., Guo, J. 2011. Biological control of take-all by phenazine-producing fluorescent Pseudomonas spp. from Chinese wheat fields. Phytopathology. 101(12):1481-1491. Interpretive Summary: Phenazine-1-carboxylic acid (PCA) is an antibiotic produced by certain strains of bacteria that live on the roots of plants. PCA is active against a wide range of plant-pathogenic fungi. In this study, PCA-producing Pseudomonas strains were isolated for the first time from the inside of wheat stems in China and then were shown to suppress take-all, the most important root disease of wheat worldwide. PCA was produced by the bacteria both in vitro and on the roots of wheat. Mutants of the bacteria that lost the ability to produce PCA also lost all or part of their biocontrol activity against take-all. These results demonstrate that antibiosis is an important mechanism by which biocontrol agents control soilborne diseases.
Technical Abstract: Take-all disease of wheat caused by the soilborne fungus Gaeumannomyces graminis var. tritici is one of the most important root diseases of wheat worldwide. Bacteria were isolated from winter wheat from irrigated and rainfed fields in Hebei and Jiangsu provinces in China, respectively. Samples from rhizosphere soil, roots, stems and leaves were plated onto King’s B agar and 553 isolates were selected. On the basis of in vitro tests, 105 isolates (19% of the total) inhibited G. graminis var. tritici and all were identified as Pseudomonas spp. by ARDRA analysis. Based on biocontrol assays, 13 strains were selected for further analysis. All of them aggressively colonized the rhizosphere of wheat and suppressed take-all. Three of the 13 strains (HC9-07, HC13-07 and JC14-07) had genes for the biosynthesis of phenazine-1-carboxylic acid (PCA), but none had genes for the production of 2,4-diacetylphloroglucinol, pyoluteorin or pyrrolnitrin. High-pressure liquid chromatography (HPLC) analysis of two-day-old cultures confirmed that HC9-07, HC13-07 and JC14-07 produced PCA, but no other phenazines were detected. HPLC-Q-Tof 2 mass spectrometry analysis of extracts from roots of spring wheat colonized by HC9-07, HC13-07 or Pseudomonas fluorescens 2-79 demonstrated that all three strains produced PCA in the rhizosphere. Loss of phenazine production by strain HC9-07 resulted in a loss of biocontrol activity. Analysis of DNA sequences within the key phenazine biosynthesis gene phzF and of 16S rDNA indicated that strains HC9-07, HC13-07 and JC14-07 were similar to the well-described PCA producer P. fluorescens 2-79. This is only the second report of 2-79-like bacteria being isolated outside of eastern Washington State, USA.