First occurrence of resistance to strobilurin fungicides in Microdochium nivale and Microdochium majus from French naturally infected wheat grains.
BACKGROUND
Microdochium nivale (Fr.) Samuels & Hallet and Microdochium majus (Wollenweber) belong to the Fusarium ear blight (FEB) fungal complex affecting cereals. In 2007 and 2008, major Microdochium sp. infestations were observed in France, and the efficacy of strobilurins was found to be altered in some field trials. The aim of this study was to determine the sensitivity to strobilurins of French isolates of Microdochium and to characterise the possible mechanisms of resistance.


RESULTS
Half of the strains collected in 2007 were resistant to strobilurins, and most also displayed strong resistance to benzimidazoles. Strobilurin resistance was found mostly in M. majus isolates. Positive cross-resistance was observed between all strobilurins tested, but not with the phenylpyrrole derivative fludioxonil and the various classes of sterol biosynthesis inhibitors (SBIs). In most strains, resistance was correlated with the G143A substitution in cytochrome b, the molecular target of strobilurins. Two other mechanisms were also detected at lower frequencies.


CONCLUSIONS
This is the first report of strobilurin resistance in Microdochium. Several resistance mechanisms have evolved independently in populations and may have different impacts on field efficacy. This makes the accurate detection and quantification of QoI resistance difficult. The management of field resistance and efficacy must be adapted to take these findings into account.
Walker
Anne-Sophie
AS
INRA, UMR 1290 BIOGER-CPP, Route de St Cyr, F-78000 Versailles, France. walker@versailles.inra.fr
Auclair
Christiane
C
Gredt
Michel
M
Leroux
Pierre
P
D000595:Amino Acid Sequence; D001483:Base Sequence; D045303:Cytochromes b / Q000737:chemistry / Q000235:genetics; D025141:Drug Resistance, Fungal / Q000235:genetics; D002523:Edible Grain / Q000382:microbiology; D005602:France; D005659:Fungicides, Industrial / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D008689:Methacrylates / Q000494:pharmacology*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D011110:Polymorphism, Genetic; D014908:Triticum / Q000382:microbiology*; D013098:Xylariales / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000502:physiology
D005659:Fungicides, Industrial; D008689:Methacrylates; D045303:Cytochromes b