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2010 APS Annual Meeting


Demethylation inhibitor (DMI) fungicide resistance mechanism in Sclerotinia homoeocarpa causing dollar spot in turfgrasses
B. MA (1), L. P. Tredway (1)
(1) North Carolina State University, Raleigh, NC, U.S.A.
Phytopathology 100:S75

The cytochrome P450 sterol 14α-demethylase gene (ShCYP51) in Sclerotinia homoeocarpa was cloned and sequenced. ShCYP51 gene was 1680 bp in length and contained two introns of 53 bp and 57 bp located after nucleotide positions in 247 and 498, respectively. The deduced amino acid sequence had a similarity of 73.0, 70.5 and 54.5% to the CYP51 genes from Monilinia fructicola, Botryotinia fuckeliana, and Venturia inaequalis, respectively. An ~1700 bp fragment in the upstream region of the gene was also amplified and sequenced. It was predicted to have two promoters located at the base pair position of -122 to -172 and -791 to -841 of the gene, respectively. The sensitivities of 43 S. homoeocarpa isolates to DMI fungicide were determined in vitro using a discriminatory dose of 0.02 µg/ml of propiconazole. The ShCYP51 genes and the promoter regions from those isolates were sequenced and compared. Three types of point mutation were detected among 12 isolates; however, none of them were associated with DMI sensitivity. No inserts or repeats was found in the promoter region from any of the isolates. Real-time PCR was used to quantify ShCYP51 gene expression in six sensitive and six resistant isolates, and no difference was found between the two types of isolates. Results from this study show that point mutation and over-expression of the ShCYP51 gene and modifications of the gene’s promoter region are not the mechanisms operating in S. homoeocarpa leading to the resistance to DMI fungicide.

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