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Resistance

Incidence of Carboxin Resistance in Ustilago nuda. G. Newcombe, Research Station, Agriculture Canada, 195 Dafoe Road, Winnipeg, MB, Canada, R3T 2M9; P. L. Thomas, Research Station, Agriculture Canada, 195 Dafoe Road, Winnipeg, MB, Canada, R3T 2M9. Phytopathology 81:247-250. Accepted for publication 4 October 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/Phyto-81-247.

In planta validation and an appropriate in vitro assay confirmed the existence of carboxin resistance within some European field isolates of Ustilago nuda. Carboxin resistance was not found within the 1988–1989 Canadian population (260 field isolates tested) of U. nuda, nor within a worldwide population collected before the use of carboxin (96 field isolates tested). Indirect in vitro evidence was obtained, which indicated that the in planta effects of seed treatment with carboxin were fungicidal rather than fungistatic.