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In Planta Production and Antibody Neutralization of the Ptr Necrosis Toxin from Pyrenophora tritici-repentis. L. Lamari, Department of Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada; G. M. Ballance, N. P. Orolaza, and R. Kowatsch. Department of Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada. Phytopathology 85:333-338. Accepted for publication 7 December 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-333.

Pyrenophora tritici-repentis, the causal agent of tan spot of wheat, induces differentially tan necrosis and chlorosis in wheat. There are currently four pathotypes described in P. tritici-repentis, based on the ability of the pathogen to induce tan necrosis and chlorosis. Previous studies have demonstrated that a host-selective toxin, produced in culture by nec+ isolates, will produce tan necrosis in sensitive cultivars. 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–derived toxin and with purified Ptr necrosis toxin in terms of temperature 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 with nec isolates. For cultivars inoculated with nec+ isolates, regardless 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 constitutively.

Additional keywords: Drechslera, polyclonal antibodies, Western blot.