Rapid Development of Fungicide Resistance by Sclerotinia homoeocarpa on Turfgrass

Abstract

Dollar spot, caused by Sclerotinia homoeocarpa, is the most prevalent and economically important turfgrass disease in North America. Increasing levels of fungicide resistance, coupled with tightening environmental scrutiny of existing fungicides, has left fewer options for managing dollar spot. More knowledge about S. homoeocarpa populations is needed to improve dollar spot management strategies, especially with respect to minimizing the development of fungicide resistance. Population diversity of S. homoeocarpa was examined using inter-simple sequence repeat markers and vegetative compatibility assays. Two subgroups were found in S. homoeocarpa field populations on both fairway and putting green turfgrass at a research field in Wisconsin. These subgroups were genetically different, vegetatively incompatible, and had different fungicide sensitivities. The frequency of the two genetic subgroups differed significantly between the fairway and putting green, but was uniform within the fairway or within the green. Population dynamics of S. homoeocarpa in response to two systemic fungicides (thiophanate-methyl and propiconazole) were assessed based on in vitro fungicide sensitivity. Dynamics of S. homoeocarpa populations depended on the presence of fungicide-resistant isolates in the initial populations before fungicide applications and changed rapidly after fungicide applications. Shifting of the population toward propiconazole resistance was gradual, whereas thiophanate-methyl resistance developed rapidly in the population. In conclusion, field populations of S. homoeocarpa containing genetically distinct, vegetatively incompatible groups were different on turfgrass that was managed differently, and they were changed rapidly after exposure to fungicides.

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).…”

“…With thiophanatemethyl, the qualitative (bimodal) nature of resistance can lead to control failures in the field. In previous work, significant increases were observed in the frequency of thiophanate-methyl resistance in a previously unexposed population after just two applications (9).…”

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).…”

Control Effect on Dollar Spot Disease Caused by Sclerotinia homoeocarpa under Different Application Rates and Intervals with Two Mixed Fungicides

“…동전마름병의 방제는 우리나라를 포함해 전세계적으로 살균제 살포에 의한 것이 일반적이다 (Couch, 2002;Latin, 2006;Chang et al, 2009;Kim et al, 2010). 하지만 지속 적인 살균제 살포는 약제에 대한 병원균의 선발압을 높이 기 때문에 약제 저항성이 문제를 초래할 수 있다 (Jo et al, 2008). 살균제에 대한 S. homoeocarpa의 약제 저항성은 1960년대 후반에 발견된 이후 현재까지 다양한 농약에서 문제되어 왔다 (Cole et al, 1968;Detweiler et al, 1983; *Corresponding author:…”

“…Phone) +82-55-934-0143, Fax) +82-55-934-0146 E-mail) changsw802@hanmail.net Smith et al, 1989;Jo et al, 2008 (Warren et al, 1977;Smith et al, 1989;Shim et al, 2001;Koch et al, 2009). …”