Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/1994
Publication Date: N/A
Interpretive Summary: Soilborne plant pathogens are major yield-limiting factors in the production of food, fiber and ornamental crops. Take-all, caused by the fungus Gaeumannomyces graminis var. tritici, is the most important root disease of wheat in the U.S. and worldwide. The isolation and identification of G.g. tritici from diseased tissue can be difficult. Take- -all lesions commonly become colonized by other fungi that interfere with recovery of the pathogen. Furthermore, because G.g. tritici typically does not sporulate in culture, routine identification must rely on cultural characteristics and pathogenicity tests. The significance of this research is that it describes a simple medium for the one-step isolation and identification of G.g. tritici. This medium will greatly reduce the time it takes to isolate the take-all pathogen. It will be very useful to plant disease diagnosticians.
Technical Abstract: Isolation of Gaeumannomyces graminis var. tritici strain, causal agent of take-all, from wheat tissues often is complicated by the presence of Pythium spp., Rhizoctonia spp., Fusarium spp. or secondary fungal colonists. Because G.g. tritici does not typically sporulate in culture, identification of putative isolates is based on cultural characteristics, pathogenicity tests, and production of perithecia on infected tissue. A semiselective medium designated R-PDA was developed that aids in the isolation and identification of G.g. tritici. The medium consists of dilute potato-dextrose agar amended with 100 ug/ml rifampicin and 10 ug/ml tolclofosmethyl. Identification of G.g. tritici is aided based on its ability to alter the color of rifampicin in R-PDA from orange to purple. This reaction occurs in as little as 24 h. R-PDA was more effective in isolating putative isolates of G.g. tritici from wheat with symptoms of take-all than was SM-GGT3, another semiselective medium for G. graminis var. tritici.