Induced overexpression of cytochrome P450 sterol 14α-demethylase gene (CYP51) correlates with sensitivity to demethylation inhibitors (DMIs) in Sclerotinia homoeocarpa.

Background: The fungus Sclerotinia homoeocarpa causes dollar spot, the most important turfgrass disease worldwide. Demethylation inhibitor (DMI) fungicides have been relied upon heavily to manage this disease. Presently, populations of S. homoeocarpa with reduced sensitivity or resistance to DMIs are widespread in the United States.

Results: Cytochrome P450 sterol 14α-demethylase (ShCYP51) and its flanking regions were identified and sequenced in 29 isolates of S. homoeocarpa with a range of DMI sensitivities. No modifications were found in the gene coding and upstream regions that were consistently related to DMI sensitivity. In the absence of propiconazole, ShCYP51 was expressed at a similar low level among DMI baseline and resistant isolates. In the presence of propiconazole, DMI-resistant isolates were induced to express ShCYP51 at significantly higher levels than baseline isolates by propiconazole at 5 mg L(-1) for 5 h or at 0.5 mg L(-1) for 72 h. The ShCYP51 expression level after 72 h exposure to 0.5 mg L(-1) of propiconazole was linearly related to EC50 values and ΔRG (the change in relative growth rate over time), with R(2) values equal to 83.7 and 90.0% respectively.

Conclusion: Induced overexpression of ShCYP51 in resistant isolates following DMI exposure is an important factor determining DMI sensitivity in S. homoeocarpa.