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Physiology and Biochemistry

Cultivar-Specific Toxicity of Culture Filtrates of Pyrenophora tritici-repentis. A. Tomás, Graduate research assistant, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506; W. W. Bockus, Associate professor, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506. Phytopathology 77:1337-1340. Accepted for publication 22 April 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1337.

Pyrenophora tritici-repentis was grown in stationary liquid cultures in a modified Fries medium with low sucrose. Cellfree culture filtrates were concentrated to one-fifth of the original volume, adjusted to pH 6.8, and infiltrated into wheat plants with a Hagborg device. All P. tritici-repentis isolates tested produced a toxic compound(s) in culture that induced typical tan spot symptoms upon infiltration into susceptible wheat plants. Large necrotic areas with or without halos developed in highly susceptible TAM 105 plants. Resistant Red Chief developed only a faint chlorosis, and highly resistant Larker barley showed no symptoms. Ten wheat cultivars ranging from highly susceptible to highly resistant were compared for their reactions to pathogen inoculation and toxic culture filtrate application. Sensitivity to the toxic filtrate was highly correlated with susceptibility to the fungal pathogen, suggesting that disease resistance may be due, at least in part, to insensitivity to the toxin(s). The results obtained with the 10 wheat cultivars suggest that toxic culture filtrates could be used in screening for tan spot resistance.