Update on mechanisms of azole resistance in <i>Mycosphaerella graminicola</i> and implications for future control

This review summarises recent investigations into the molecular mechanisms responsible for the decline in sensitivity to azole (imidazole and triazole) fungicides in European populations of the Septoria leaf blotch pathogen, Mycosphaerella graminicola. The complex recent evolution of the azole target sterol 14α-demethylase (MgCYP51) enzyme in response to selection by the sequential introduction of progressively more effective azoles is described, and the contribution of individual MgCYP51 amino acid alterations and their combinations to azole resistance phenotypes and intrinsic enzyme activity is discussed. In addition, the recent identification of mechanisms independent of changes in MgCYP51 structure correlated with novel azole cross-resistant phenotypes suggests that the further evolution of M. graminicola under continued selection by azole fungicides could involve multiple mechanisms. The prospects for azole fungicides in controlling European M. graminicola populations in the future are discussed in the context of these new findings.