Purification and characterization of a host-selective necrosis toxin from Pyrenophora tritici-repentis

Abstract

Isolates of Pyrenophora tritici-repentis, the causal agent of tan spot, cause necrosis only, chlorosis only or necrosis and chlorosis as symptoms of infection on appropriate wheat differentials. A toxin has been purified from a culture filtrate of a necrosis-only isolate. The toxin produces necrosis if it is infiltrated into the leaves of cultivars susceptible to the isolate but is without effect on cultivars resistant to the isolate. The toxin was purified by gel filtration and ion exchange chromatography and shown to be a protein. Sodium dodecyl sulphate polyacrylamide gel electrophoresis was used to show the toxin purity as well as estimate a protein molecular weight of 13900. The amino acid composition and molar extinction were determined. Proteolytic digestion or treatment of the purified toxin under denaturing conditions destroyed toxin activity. Infiltration of 10 −13-10 −14 moles of purified toxin into susceptible cultivars will produce necrosis.