USE OF A POLYMERASE CHAIN-REACTION ASSAY TO AID IN IDENTIFICATION OF GAEUMANNOMYCES-GRAMINIS VAR GRAMINIS FROM DIFFERENT GRASS HOSTS

A previously described polymerase chain reaction (PCR) assay results in the amplification of a 188-bp product from Gaeumannomyces graminis var, graminis fungal template DNA derived from boiled fungal mycelia. Similar results are obtained when mycelia are grown on potato-dextrose agar, Czapek solution agar, and Luria-Bertani agar, but not on a medium selective for Gaeumannomyces (SM-7). Amplification of this specific DNA fragment combined with observation of lobed hyphopodia can be used to identify a Gaeumannomyces-like isolate as G. g. graminis, even if perithecia are never produced by the isolate. All 40 ''presumptive'' G. g. graminis test isolates produced lobed hyphopodia in culture and the 188-bp PCR product, but only 19 of these isolates produced mature perithecia. Additional amplification products (i.e., products other than the expected 188-bp product) were also obtained with this assay. Although the sizes and numbers of these additional products varied among isolates, they correlated with the particular grass host from which the isolates were derived (bermudagrass, St. Augustinegrass, or rice), which suggested that the grass host selected specific pathogen genotypes. For example, isolates from bermudagrass consistently produced a DNA band pattern that was distinct from the DNA band pattern produced by isolates from St. Augustinegrass.