Variation in response of three Epichloë species, causal agents of ‘choke disease’ in grasses, to the novel fungicide mefentrifluconazole

Abstract The fungal endophytes of the Epichloë genus produce stromata, which are external structures that prevent grasses from flowering and producing seeds, causing economic losses in grass-based crops due to a condition known as 'choke disease.' This study aimed to examine the impact of a new fungicide, mefentrifluconazole, on the mycelium growth of Epichloë fungi. The results revealed that percent growth inhibition (PGI) values recorded with mefentrifluconazole varied among the three Epichloë species tested, with the highest value in E. festucae (85.43 ± 0.81%) and the lowest in E. typhina (43.04 ± 12.00%). Compared to other fungicides (azoxystrobin and fenpropidin), mefentrifluconazole had a weak effect at low concentrations in two of the three Epichloë species tested. Additionally, in each of the tested fungal species, mefentrifluconazole had different effect compared to other fungicides (it was the most effective fungicide in E. festucae , the least effective in E. typhina , and in E. clarkii, its effectiveness was between azoxystrobin and fenpropidin, taking into account the highest possible PGI in a given species). When analyzing the EC 50 values of all tested fungicides, it is difficult to determine the most effective inhibitor for all three Epichloë species. These findings provide new insights into the management of 'choke disease' in grasses. The variation in response of the three species to the novel fungicide mefentrifluconazole highlights the importance of studying different species of Epichloë simultaneously.