Evolution of Mycosphaerella graminicola resistance to epoxiconazole and pyrifenox in northern France.

DMIs have been for many years the most used antifungal compounds against Septoria tritici blotch caused by Mycosphaerella graminicola, the most important foliar disease on winter wheat worldwide. Their use leads to a development and widespread of isolates with reduced sensitivity in several populations around Europe, especially in France. Here, we investigated the resistance level to epoxiconazole and pyrifenox of 48 M. graminicola isolates (24 from 2009 and 24 from 2011) sampled in Nord-Pas de Calais (France) from two untreated plots naturally infected by the fungus. The resistance levels were determined by microplate assays at 10 different concentrations for each fungicide (geometric progression x 3.5). Overall, IC50 (half maximal inhibitory concentration) values were slightly higher in the 2011-isolates compared to the 2009-isolates. For the 2009-isolates, IC50 values ranged from 0.14 mg/L to 2.25 mg/L and from 0.10 mg/L to 2.19 mg/L for epoxiconazole and pyrifenox, respectively, while IC50 values for 2011-isolates ranged from 0.10 mg/L to 22.13 mg/L and from 0.07 mg/L to 11.63 mg/L for epoxiconazole and pyrifenox, respectively. The determination of resistant factors (IC50 resistant isolate/IC50 sensitive isolate) revealed an increase of rates of isolates showing a resistant factor higher than 100 from 21% to 62 % for epoxiconazole and from 8% to 42% for pyrifenox between 2009 and 2011. Furthermore, statistical analyses revealed a positive correlation between resistances to epoxiconazole and pyrifenox in both years, indicating that most of isolates resistant for epoxiconazole are also resistant for pyrifenox. This study shows a shift in sensitivity to epoxiconazole and pyrifenox in northern France between 2009 and 2011 and suggests a relationship between resistance to epoxiconazole and pyrifenox in M. graminicola.

Citation

C Deweer, A Siah, K Sahmer, P Halama. Evolution of Mycosphaerella graminicola resistance to epoxiconazole and pyrifenox in northern France. Communications in agricultural and applied biological sciences. 2012;77(3):109-15

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PMID: 23878964

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