Virulence of collections ofUstilago avenaeandUstilago kollerisampled from oat fields in Canada during 1995-1999¹

Abstract

Loose and covered smut of oat are effectively controlled through the use of resistant cultivars or carbathiin seed treatment in Canada. The potential for development of carbathiin-insensitive genotypes or of races with new virulence genes or new virulence gene combinations makes it desirable to regularly monitor the pathogen populations to detect changes. This study was conducted to define the virulence spectrum and carbathiin sensitivity of isolates of Ustilago avenae (Pers.) Rostr. and Ustilago kolleri Wille in Canada. Smutted oat panicles were collected from 17 farm fields in Manitoba and Saskatchewan during annual surveys from 1995 to 1999. Four more collections were obtained from collaborators in Ontario and Alberta. Nineteen of the collections were identified as U. avenae and two were identified as U. kolleri. All the isolates were found to be sensitive to the fungicide carbathiin at 1 µg/mL, using a petri dish test. The virulence of the smut isolates was determined using the Canadian oat smut differential set. Eleven races, virulent on 3-10 differential host lines, were identified from the 19 isolates of U. avenae, and 2 races, virulent on 5 and 7 differential host lines, respectively, were identified from the 2 isolates of U. kolleri. None of the races were virulent on the oat differential lines Fulgham, Camas, or Markton or the oat cultivars AC Medallion, AC Assiniboia, AC Belmont, AC Preakness, or Tibor, but races virulent to cultivars AC Lotta, CDC Boyer, and Derby were detected. Carbathiin seed treatment and current resistant oat cultivars are still effective for the control of loose and covered smut of oats in Canada.