IN PLANTA PRODUCTION AND ANTIBODY NEUTRALIZATION OF THE PTR NECROSIS TOXIN FROM PYRENOPHORA-TRITICI-REPENTIS

Pyrenophora tritici-repentis, the causal agent of tan spot of wheat, i nduces differentially tan necrosis and chlorosis in wheat. There are c urrently four pathotypes described in P. tritici-repentis, based on th e ability of the pathogen to induce tan necrosis and chlorosis. Previo us studies have demonstrated that a host-selective toxin, produced in culture by nec(+) isolates, will produce tan necrosis in sensitive cul tivars. This study shows that a necrosis-producing toxin is present in the intercellular washing fluid (IWF) of leaves infected with nec(+) isolates. Comparison of the toxin in the IWFs with culture filtrate-de rived toxin and with purified Ptr necrosis toxin in terms of temperatu re stability, size, immunological identity, host range of sensitivity, and isolate source led to the conclusion that the toxin found in IWFs is Ptr necrosis toxin, which is produced in planta. This is the first report of in planta production and release of the Ptr necrosis toxin by nec(+) isolates of P. tritici-repentis. IWFs containing toxin were produced only from leaves inoculated with nec(+) isolates and never wi th nec(-) isolates. For cultivars inoculated with nec(+) isolates, reg ardless of whether the cultivars were susceptible or resistant, toxin was present in the IWF indicating that toxin production by the nec(+) isolates is independent of the host interactions and may be produced c onstitutively.