Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2008
Publication Date: 7/20/2008
Citation: Kwak, Y., Bakker, P.A., Glandorf, D.C., Paulitz, T.C., Weller, D.M. 2008. Diversity, virulence and 2,4-diacetylphloroglucinol sensitivity of Gaeumannomyces graminis var. tritici isolates from Washington State.. American Phytopathological Society Annual Meeting. Interpretive Summary:
Technical Abstract: Populations of 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas fluorescens buildup in soils that have undergone continuous wheat or barley monoculture, resulting in take-all decline (TAD). We tested whether Gaeumannomyces graminis var. tritici (Ggt) isolates (causal agent of take-all) in monoculture wheat or barley fields become less sensitive to DAPG because of frequent exposure to the antibiotic. Over 184 isolates of Ggt were baited from roots of wheat and native grasses growing in fields with different cropping histories near Lind, Ritzville, Pullman and Almota, WA. Isolates were characterized using morphological traits, growth on a semi-selective medium, G. graminis variety-specific PCR primers and pathogenicity tests. The sensitivity of 163 Ggt isolates to DAPG was determined by measuring radial growth of the isolates on agar medium supplemented with the antibiotic. Sensitivity of the isolates to DAPG was normally distributed. The ED90 was 3.14 to 4.47 µg ml-1 for sensitive isolates; 4.48 to 6.24 µg ml-1 for moderately sensitive isolates; and 6.25 to 11.1 ml- 1 for less sensitive isolates. Five Ggt isolates were extremely sensitive to DAPG (ED90 <1 µg ml-1). Isolate sensitivity to DAPG was not correlated with geographic origin or cropping history of the field. There was no correlation between virulence on wheat and geographic origin, and no correlation occurred between virulence and sensitivity to DAPG. Unexpectedly, Phialophora spp. comprised 25% and 95% of putative take-all pathogens isolated from fields near Almota and Pullman that were direct-seeded to continuous wheat or barley. All Phialophora spp. isolates were insensitive (mean ED90 is 22.44 µg ml-1) to DAPG.