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Diversity, Virulence, and 2,4-Diacetylphloroglucinol Sensitivity of Gaeumannomyces graminis var. tritici Isolates from Washington State

First and fourth authors: Department of Plant Pathology, Washington State University, Pullman, WA 99164-6430; second author: Plant-Microbe Interactions, Department of Biology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; third author: GMO office, Expert Centre of Substances, National Institute of Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands; and fifth and sixth authors: USDA-ARS, Root Disease and Biological Control Research Unit, Pullman, WA 99164-6430. First, second, third, and sixth authors contributed equally to this work.

We determined whether isolates of the take-all pathogen Gaeumannomyces graminis var. tritici become less sensitive to 2,4-diacetylphloroglucinol (2,4-DAPG) during wheat monoculture as a result of exposure to the antibiotic over multiple growing seasons. Isolates of G. graminis var. tritici were baited from roots of native grasses collected from noncropped fields and from roots of wheat from fields with different cropping histories near Lind, Ritzville, Pullman, and Almota, WA. Isolates were characterized by using morphological traits, G. graminis variety-specific polymerase chain reaction and pathogenicity tests. The sensitivity of G. graminis var. tritici isolates to 2,4-DAPG was determined by measuring radial growth of each isolate. The 90% effective dose value was 3.1 to 4.4 μg ml^--1 for 2,4-DAPG-sensitive isolates, 4.5 to 6.1 μg ml^--1 for moderately sensitive isolates, and 6.2 to 11.1 μg ml^--1 for less sensitive isolates. Sensitivity of G. graminis var. tritici isolates to 2,4-DAPG was normally distributed in all fields and was not correlated with geographic origin or cropping history of the field. There was no correlation between virulence on wheat and geographical origin, or virulence and sensitivity to 2,4-DAPG. These results indicate that G. graminis var. tritici does not become less sensitive to 2,4-DAPG during extended wheat monoculture.

Additional keywords:biological control, Pseudomonas fluorescens, take-all.