In Vitro SDHI Fungicide Insensitivity and Mutations in <i>Sdh</i> , <i>β‐Tubulin</i> and <i>Cyp51</i> of <i>Clarireedia</i> spp., Causing Dollar Spot in Turfgrass in Georgia, USA

ABSTRACT Dollar spot, caused by Clarireedia spp., diminishes turf quality, affecting both aesthetics and sport playability on the surface. Fungicides are the primary means of disease control; however, repeated applications may lead to resistance development and reduced fungicide efficacy in the field. In this study, 79 Clarireedia spp. isolates collected from turfgrasses in Georgia and previously characterised for thiophanate‐methyl and propiconazole sensitivities, were assessed for in vitro sensitivity against boscalid, a succinate dehydrogenase inhibitor (SDHI) fungicide, using fungicide‐amended agar assays. Overall, 32.9% isolates showed reduced sensitivity to boscalid and 24% isolates exhibited multiple fungicide insensitivities. One isolate of C. jacksonii and eight of C. monteithiana , representing varying sensitivity levels, were examined further for mutations in Sdh , β‐tubulin and Cyp51 gene sequences associated with resistance to boscalid, thiophanate‐methyl and propiconazole, respectively. Amino acid substitutions R61K and E63A in SdhD were linked to reduced boscalid sensitivity. The amino acid substitution E198A was also identified in the β‐tubulin gene sequence of the C. jacksonii isolate highly resistant to thiophanate‐methyl. Predicted protein structure, supported by molecular docking, suggested an effect of the identified mutations. Additionally, synonymous mutations and intronic indels were detected in Sdh genes of three highly resistant C. monteithiana isolates. No mutations in the Cyp51 were associated with propiconazole resistance in Clarireedia spp. Our findings highlight the need for continuous monitoring of fungicide sensitivity and suggest that high frequencies of isolates resistant to individual fungicides along with multiple fungicide resistant isolates may pose challenges for effective disease management.