Purification and Immunological Characterization of Toxic Components from Cultures of<i>Pyrenophora tritici-repentis</i>

To facilitate the genetic analysis of pathogenicity in the wheat-Pyrenophora tritici-repentis interaction, a host-selective toxic protein, designated ToxA, was purified from culture filtrates of this fungus. ToxA was shown to be a 13.2-kDa heat-stable protein which induced visible necrosis in sensitive wheat cultivars at an average minimum concentration of 60 nM. Polyclonal antibodies raised against ToxA were shown by Western analysis and indirect immunoprecipitation to be specific for this protein. Bioassays of immunoprecipitated protein and ToxA protein eluted from polyacrylamide gels indicated that ToxA protein is the toxic agent. Other less abundant necrosis-inducing components that are chromatographically and immunologically distinct from ToxA were also detected in culture filtrates of P. tritici-repentis. These components were found in cationic and anionic protein fractions and, like ToxA, induced cultivar-specific necrosis.