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Type: Journal article
Title: Reduced sensitivity of Uncinula necator to sterol demethylation inhibiting fungicides in southern Australian vineyards
Author: Savocchia, S.
Stummer, B.
Wicks, T.
Van Heeswijck, R.
Scott, E.
Citation: Australasian Plant Pathology, 2004; 33(4):465-473
Publisher: C S I R O Publishing
Issue Date: 2004
ISSN: 0815-3191
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 micropropagated 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.
Keywords: Fungicide resistance; grapevine powdery mildew
RMID: 0020041197
DOI: 10.1071/AP04066
Appears in Collections:Agriculture, Food and Wine publications

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