Fungicide Resistance Evolving in Population in Estonia.

Ramularia leaf spot caused by the fungus , has recently become widespread in Estonian barley fields. Currently, disease control in barley fields relies on SDHI and DMI fungicides, which might be threatened by isolates that are well-adapted to fungicide pressure. In a two-year study, 353 isolates were collected from spring barley fields in Estonia. A total of 153 isolates were examined for sensitivity to azoles (DMIs; prothioconazole-desthio, epoxiconazole, mefentrifluconazole) and succinate dehydrogenase inhibitors (SDHIs; boscalid, fluxapyroxad). Epoxiconazole was the least effective and a new fungicide mefentrifluconazole was the most effective DMI. Among SDHIs, fluxapyroxad was more effective than boscalid. Also, single isolates with high resistance to tested fungicides occurred, which could affect fungicide control of the pathogen. The entire collection of was analysed for mutations in fungicide target proteins. Six mutations were identified in gene, the most dominant being I381T, I384T, and S459C. Also, numerous point mutations in the gene were present. The mutation G143A in strobilurin target protein CytB dominates in over 80% of the population, confirming the low efficacy of strobilurin fungicides in barley disease control.