Application of a Rapid Screening Test for Selection of Bacteria Suppressive to Take-All of Wheat. D. M. Weller, USDA-ARS Plant Pathologist, USDA-ARS Plant Pathologist, 367 Johnson Hall, Washington State University, Pullman 99164. B.-X. Zhang, Visiting Scientist, Peoples Republic of China, and R. J. Cook, USDA-ARS Plant Pathologist, 367 Johnson Hall, Washington State University, Pullman 99164. Plant Dis. 69:710-713. Accepted for publication 25 January 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/PD-69-710.

An assay was developed to rapidly screen bacteria for ability to suppress take-all of wheat, caused by Gaeumannomyces graminis var. tritici. The assay entailed use of plastic, tapered tubes (2.5 cm in diameter × 16.5 cm long), each with a hole in the bottom for draining, in which 5 g of soil infested with G. graminis var. tritici as colonized oat kernels (particles 0.25–0.5 mm added at 0.15 and 0.45%, w/w) were placed on a 6.5-cm-thick column of vermiculite. Two bacteria-treated seeds were then placed on the soil and covered with a 1.5-cm-thick layer of vermiculite. After 3–4 wk, the amount of take-all on the roots was determined. Of 121 strains of fluorescent Pseudomonas spp. tested, 71 and 49% were suppressive to take-all in a nonfumigated Puget silt loam amended with the inoculum source at 0.15 and 0.45%, respectively; however, in fumigated Shano silt loam, 83 and 78% of the isolates were suppressive at these concentrations of inoculum. A significantly greater (P = 0.05) number of the strains was suppressive if obtained originally from roots grown in soil from wheat fields where take-all had declined (suppressive soil) than if obtained from roots grown in soil in which wheat had not been continuously grown (conducive soil). On the basis of the test, two new strains of fluorescent Pseudomonas spp. were selected that were suppressive to take-all in the field.

Keyword(s): biological control.