Australasian Plant Pathology

, Volume 33, Issue 4, pp 465–473 | Cite as

Reduced sensitivity of Uncinula necator to sterol demethylation inhibiting fungicides in southern Australian vineyards

  • S. Savocchia
  • B. E. Stummer
  • T. J. Wicks
  • R. van Heeswijck
  • E. S. Scott
Article

Abstract

Isolates of Uncinula necator with reduced sensitivity to triadimenol and, to a lesser extent, fenarimol have been detected in Australian vineyards. Grapevine leaves and berries affected by powdery mildew were collected from a home garden and 13 vineyards in nine viticultural regions in Australia between 1993 and 1998. Single-spore isolates of U. necator established from vines, either not exposed to DMIs (‘unexposed’ collection) or treated with DMIs (‘selected’ collection), were maintained on micro propagated grapevines in vitro. A bioassay for fungicide sensitivity was used to test 60 single-spore isolates of U. necator for sensitivity to triadimenol. Of these, 34 were tested for sensitivity to fenarimol. Mean EC50 values for the 12 unexposed isolates were 0.07 and 0.08 mg/L for triadimenol and fenarimol, respectively. For the selected isolates, mean EC50 values were 0.83 mg/L for triadimenol and 0.19 mg/L for fenarimol. In comparison with the unexposed population, there appeared to have been a shift in the selected population towards reduced sensitivity. Examination of more isolates from vineyards not exposed to DMIs may strengthen this conclusion. Cut-off EC50 values, used to define individual isolates as having reduced sensitivity, were 0.42 mg/L (resistance factor, RF = 6) for triadimenol and 0.12 mg/L (RF = 1.5) for fenarimol. The findings were consistent with the existence of cross-resistance between triadimenol and fenarimol.

Additional keywords

fungicide resistance grapevine powdery mildew 

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Copyright information

© Australasian Plant Pathology Society 2004

Authors and Affiliations

  • S. Savocchia
    • 1
    • 4
  • B. E. Stummer
    • 1
  • T. J. Wicks
    • 2
  • R. van Heeswijck
    • 3
  • E. S. Scott
    • 1
  1. 1.Discipline of Plant and Pest ScienceThe University of AdelaideGlen OsmondAustralia
  2. 2.South Australian Research and Development InstituteAdelaideAustralia
  3. 3.Discipline of Wine and HorticultureThe University of AdelaideGlen OsmondAustralia
  4. 4.National Wine and Grape Industry Centre, School of Wine and Food SciencesCharles Sturt UniversityWagga WaggaAustralia

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