Emergence of succinate dehydrogenase inhibitor resistance of Pyrenophora teres in Europe.

BACKGROUND: Net blotch caused by Pyrenophora teres is an important disease of barley worldwide. In addition to strobilurins (quinone ouside inhibitors) and azoles (demethylation inhibitors), succinate dehydrogenase inhibitors (SDHIs) are very effective fungicides for net blotch control. Recently, SDHI-resistant isolates have been found in the field. Intensive sensitivity monitoring programmes across Europe were carried out to investigate the situation concerning SDHI resistance in P. teres.

RESULTS: The first isolates with a lower sensitivity to SDHIs registered in barley were found in Germany in 2012 and carried the B-H277Y substitution in the succinate dehydrogenase enzyme. In 2013 and 2014, a significant increase in isolates with lower SDHI sensitivity was detected mainly in France and Germany, and the range of target-site mutations increased. Most of the resistant isolates carried the C-G79R substitution, which exhibits a strong impact on all SDHIs in microtitre tests. All SDHIs tested were shown to be cross-resistant. Other substitutions are gaining in importance, e.g. C-N75S in France and D-D145G in Germany. So far, no double mutants in SDH genes have been detected. Glasshouse tests showed that SDHI-resistant isolates were still controlled by the SDHI fluxapyroxad when applied preventively. To date, most isolates with C-G79R substitution have not simultaneously carried the F129L change in cytochrome b, which causes resistance towards QoI fungicides at low to moderate levels.

CONCLUSION: Several target-site mutations in the genes of subunits SDH-B, SDH-C and SDH-D with different impact on SDHI fungicides were detected. The pattern of mutations varied from year to year and between different regions. Strict resistance management strategies are recommended to maintain SDHIs as effective tools for net blotch control, especially in areas with low frequencies of resistant isolates. © 2016 Society of Chemical Industry.