Canadian Journal of Plant Pathology (2008) 30, 498-502

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J.G. Menzies (2008)
Carboxin tolerant strains of Ustilago nuda and Ustilago tritici in Canada
Canadian Journal of Plant Pathology 30 (3), 498-502
Abstract: Seed treatment with systemic fungicides is commonly used to control loose smut of barley, caused by Ustilago nuda, and loose smut of wheat, caused by Ustilago tritici. Historically, the most widely used active ingredient in these fungicides has been carboxin. Isolates of U. nuda that are resistant to carboxin have been reported in France and Italy. Three isolates of U. tritici collected in 1997 and two isolates of U. nuda collected in 1999 in Canada appeared to be insensitive to carboxin when assessed using a teliospore germination assay on carboxin-amended media. In planta, studies were conducted by inoculation of these isolates onto susceptible lines of wheat or barley with treatment or no treatment of the inoculated seed with carboxin at the recommended rate in Canada of 55 g ai carboxin / 100 kg seed or twice the rate (110 g ai carboxin/100 kg seed). When the inoculated seed was subsequently grown to heading, assessment of the percent of smutted spikes on the plants indicated that the three isolates of U. tritici and the two isolates of U. nuda were unaffected by the carboxin seed treatment at 55 g ai carboxin/100 kg seed. However, the incidence of loose smut on their respective hosts by three of these isolates was significantly reduced when the seed was treated at a rate of 110 g ai carboxin/100 kg seed. These results would suggest that these isolates of U. tritici and U. nuda are tolerant to carboxin rather than resistant, because, in general, higher doses of the fungicide in seed treatments reduced host disease incidence caused by these pathogenic isolates.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): James G. Menzies

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

Pest and/or beneficial records:

Beneficial Pest/Disease/Weed Crop/Product Country Quarant.

Ustilago nuda Barley (Hordeum vulgare)
Ustilago tritici Wheat (Triticum)