Identification of Gaeumannomyces-Graminis var. tritici and G-graminis var avenae using a DNA probe and nonmolecular methods

Fungi in the Gaeumannomyces-Phialophora complex were compared using a DNA probe and by pathogenicity and other biological tests. Isolates from cereal and grass hosts which were pathogenic on cereals were differentiated as G. graminis var. tritici or G. graminis var. avenae on the basis of pathogenicity tests on wheat and oat seedlings, ascospore measurements and comparison of growth rates on oat-leaf agar. DNA was extracted from pure cultures of these isolates and also from non-pathogenic isolates of Phialophora spp. from cereals, grasses and sedges, and from fungi of other genera. The samples were digested with restriction enzymes, separated by electrophoresis on agarose gels and hybridized with a radio-labelled DNA probe (pMSU315) known to have homology almost exclusively with DNA from fungi within the complex. Thirty-three isolates of G. graminis var. tritici and 20 of G. graminis var. avenae, previously identified by the much slower non-molecular methods, produced distinctive restriction fragment length polymorphisms after digestion with BamHI. In particular, a prominent band of a 2.9 kb fragment occurred in all isolates and was diagnostic for these two take-all pathogens. The same result was obtained using a non-radioactive method for labelling the probe. The possible value of using pMSU315 in this way as a diagnostic test for the take-all pathogens is discussed.