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Variable Chlorate Resistance in Macrophomina phaseolina from Corn, Soybean, and Soil. C. A. S. Pearson, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506; J. F. Leslie(2), and F. W. Schwenk(3). (2)(3)Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506. Phytopathology 76:646-649. Accepted for publication 22 January 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-646.

Macrophomina phaseolina isolated from soybean field soil or from corn or soybean tissue was grown on a defined medium with and without 120 mM potassium chlorate; chlorate is a nitrate analog. Growth was scored after 7 days of incubation at 30 C. Corn isolates were chlorate-resistant and grew normally, producing numerous dark microsclerotia on medium containing potassium chlorate. Isolates from soybean field soil and soybean root tissue were chlorate-sensitive. Sensitive isolates could be divided into two classes on the basis of growth on chlorate-containing medium. One class of sensitive isolates grew sparsely with a featherlike microsclerotial pattern, whereas radial growth of the other sensitive class was almost completely restricted. These observations suggest that M. phaseolina from corn and soybean differ in their ability to use certain nitrogenous compounds. Such differences might reflect metabolic abilities that could lead to host specialization within this genus.

Additional keywords: charcoal rot, host specialization, nitrogen nutrition, Rhizoctonia bataticola.