Molecular Mechanisms Involved in Qualitative and Quantitative Resistance to the Dicarboximide Fungicide, Iprodione in Sclerotinia homoeocarpa Field Isolates.

The dicarboximide fungicide class is commonly used to control Sclerotinia homoeocarpa, the causal agent of dollar spot on turfgrass. Despite frequent occurrences of S. homoeocarpa field resistance to iprodione (dicarboximide active ingredient), the genetic mechanisms of iprodione resistance have not been elucidated. In this study, 15 field isolates (seven suspected dicarboximide resistant, three multidrug resistance (MDR)-like, and five dicarboximide sensitive) were used for sequence comparison of a histidine kinase gene, Shos1, of S. homoeocarpa. The suspected dicarboximide-resistant isolates displayed nonsynonymous polymorphisms in codon 366 (isoleucine to asparagine) in Shos1, while the MDR-like and sensitive isolates did not. Further elucidation of the Shos1 function, using polyethylene glycol–mediated protoplast transformation indicated that S. homoeocarpa mutants (Shos1I366N) from a sensitive isolate gained resistance to dicarboximides but not phenylpyrrole and polyols. The deletion of Shos1 resulte...