Azole sensitivity in Leptosphaeria pathogens of oilseed rape: the role of lanosterol 14 alpha-demethylase

Lanosterol 14-α demethylase is a key enzyme intermediating the biosynthesis of ergosterol in fungi,
and the target of azole fungicides. Studies have suggested that Leptosphaeria maculans and L.
biglobosa, the causal agents of phoma stem canker on oilseed rape, difer in their sensitivity to some
azoles, which could be driving pathogen frequency change in crops. Here we used CYP51 protein
modelling and heterologous expression to determine whether there are interspecifc diferences at the
target-site level. Moreover, we provide an example of intrinsic sensitivity diferences exhibited by both
Leptosphaeria spp. in vitro and in planta. Comparison of homologous protein models identifed highly
conserved residues, particularly at the azole binding site, and heterologous expression of LmCYP51B
and LbCYP51B, with fungicide sensitivity testing of the transformants, suggests that both proteins are
similarly sensitive to azole fungicides fusilazole, prothioconazole-desthio and tebuconazole. Fungicide
sensitivity testing on isolates shows that they sometimes have a minor diference in sensitivity in vitro
and in planta. These results suggest that azole fungicides remain a useful component of integrated
phoma stem canker control in the UK due to their efectiveness on both Leptosphaeria spp. Other
factors, such as varietal resistance or climate, may be driving observed frequency changes between
species.