Geographic Distribution of Fungicide-Insensitive Sclerotinia homoeocarpa Isolates from Golf Courses in the Northeastern United States

Abstract

Chemical management of dollar spot in turf may lead to the development of Sclerotinia homoeocarpa populations with reduced fungicide sensitivity. The objective of this study was to determine the scope of S. homoeocarpa insensitivity to fungicides commonly used to control dollar spot on golf courses in the northeastern United States. A total of 965 and 387 isolates of S. homoeocarpa from intensively or individually sampled sites, respectively, were evaluated for in vitro sensitivity to iprodione, propiconazole, and thiophanate-methyl. Mean baseline sensitivities to iprodione and propiconazole were 0.2763 and 0.0016 μg a.i. ml–1, respectively, and all baseline isolates were sensitive to thiophanate-methyl at 1,000 μg a.i. ml–1. When compared with the baseline population, 14 and 18 of 20 total populations were less sensitive to iprodione and propiconazole, respectively. Individually sampled isolates obtained from fairways, putting greens, or tees were less sensitive to iprodione and propiconazole when compared with the baseline. For thiophanate-methyl, five populations were sensitive, six were resistant, and the remaining nine populations contained various proportions (2 to 92%) of resistant isolates. Individually sampled isolates obtained from fairways and putting greens were evaluated for associations in sensitivity among the three fungicides. A weak but positive correlation in sensitivity to iprodione and propiconazole was observed for isolates resistant to thiophanate-methyl but correlations for sensitive isolates were not significant. Furthermore, isolates with highly reduced sensitivity to iprodione clustered in a narrow range of propiconazole sensitivity. These data suggest the possible existence of resistance mechanisms common to diverse fungicide classes. Overall, results indicate that insensitivity of S. homoeocarpa to iprodione, propiconazole, and thiophanate-methyl exists in varying degrees on golf courses in the northeastern United States.

Resistance of KansasSclerotinia homoeocarpaIsolates to Thiophanate-Methyl and Determination of Associated β-Tubulin Mutation

“…Of those, only two were sensitive to thiophanate-methyl. These results are similar to studies in other states and regions that detected a high frequency of resistance (1,9,10,25). Detailed application histories were not available, but most golf courses had some history of applying thiophanatemethyl ranging from rare (once per year or less) to occasional (2-3 times per year).…”

“…This nucleotide sequence was BLAST searched against the National Center for Biotechnology Information (NCBI) Microbes sequence database (http://blast.ncbi.nlm.nih.gov/Blast.cgi) to locate the β-tubulin gene within the contig. Serial Cloner 2.5 (http://serialbasics.free.fr) was used to identify start and stop codons and determine the β-tubulin gene structure by sequence homology with the known ascomycete β-tubulin sequences benA (AN1182) of Aspergillus nidulans and the β-tubulin gene (BC1G_00122) of Botryotinia fuckeliana (strain B05.10) (19,25). Sequence searches of the contig from the reference isolate MB01 against the NCBI Microbes sequence database revealed a putative β-tubulin gene with sequence similarity to known ascomycete β-tubulin genes.…”

“…Specifically, resistance to MBC fungicides was first reported in the 1970s in isolates from several areas in the eastern and midwestern United States (30) and since then has been documented in numerous other locations (1,2,5,10,25). Sensitivity of S. homoeocarpa isolates to MBC fungicides has not been examined in Kansas.…”

Overexpression of ShCYP51B and ShatrD in Sclerotinia homoeocarpa Isolates Exhibiting Practical Field Resistance to a Demethylation Inhibitor Fungicide

“…Disease management of turf for dollar spot requires high inputs of fungicides from several chemical classes, and the sterol DMI (demethylation inhibitor) class is commonly used for preventative and curative control (14). Unfortunately, recent investigations indicate that field isolates of S. homoeocarpa have begun to exhibit decreased sensitivity to this fungicide class and others in the United States (14,27,32,33).Several recent publications reported the reduced field efficacy of the active DMI ingredient propiconazole for controlling dollar spot as well as the reduced propiconazole sensitivity of S. homoeocarpa field isolates via in vitro growth assays (15,32,33). Most recently, Popko et al investigated the association of propiconazole field efficacy and the in vitro sensitivity of S. homoeocarpa isolates recovered from turf of five New England sites (four with previous DMI exposure and one baseline site) (32).…”

“…Disease management of turf for dollar spot requires high inputs of fungicides from several chemical classes, and the sterol DMI (demethylation inhibitor) class is commonly used for preventative and curative control (14). Unfortunately, recent investigations indicate that field isolates of S. homoeocarpa have begun to exhibit decreased sensitivity to this fungicide class and others in the United States (14,27,32,33).…”