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Abstract :
[en] Mycosphaerella graminicola strains were isolated from symptomatic winter wheat (Triticum aestivum) and spelt (Triticum spelta) leaves sampled across the Grand-Duchy of Luxembourg. In total, 484 strains were isolated from winter wheat, and 31 from spelt leaves. The sensitivity profiles of these strains towards azoxystrobin (Amistar®, Syngenta Agro GmbH, Germany) and against epoxiconazole (Opus®, BASF Belgium NV/S A, Brussels, Belgium) were assessed in microplates, allowing to test 10 different concentrations for each active substance (0, 0.00316, 0.01, 0.0316, 0.1, 0.316, 1, 3.16, 10 and 31.6μg/mL). 100μ g/mL of salicylhydroxamic acid (SHAM) was also added to the medium, in order to prevent the strains
from using alternative respiration. Results of the sensitivity tests for azoxystrobin showed a dose-dependent decrease of in vitro growth for all the strains. During both years, strains could be divided into two distinct sub-populations in relation to their azoxystrobin sensitivity, thus forming a bimodal distribution commonly reported to be associated with a single gene-mediated resistance. For wheat, the
dominant sub-population was the one showing full resistance to azoxystrobin.
The results of the sensitivity tests to epoxiconazole in liquid media showed a dose-dependent
decrease of fungal growth for all the strains tested. The EC50 values followed an unimodal
distribution. When the sensitivity distribution of the strains collected in 2008 (n=379) was
compared to that observed in 2007, although the populations have remained unimodal, a minor shift towards less sensitive populations was observed. Compared to strains originating from wheat, the spelt strains were more sensitive towards both fungicides (p ≤ 0.001).
