Vegetative Compatibility and Seasonal Variation Among Isolates of Sclerotinia homoeocarpa

Abstract

Dollar spot of amenity turf, caused by Sclerotinia homoeocarpa, occurs in two seasonal epidemics in the northern United States, one from May to late July and a second from mid-August through October. It is not known whether these seasonal epidemics are the result of multiple species or due to seasonal variation within a single species. Isolates of S. homoeocarpa were collected from dollar spot lesions obtained from golf courses in Michigan, Illinois, and Wisconsin. Vegetative compatibility reactions between isolates identified six vegetative compatibility groups (VCGs) among more than 1,300 isolates collected from the eight locations. Most VCGs were present throughout the season, but one was generally recovered only in the late epidemic. Sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS1) were identical among VCGs, indicating that the VCGs represent a single species. The results of this study suggest that the seasonal dollar spot epidemics observed in the northern United States are caused by a single species.

Geostatistical Analysis of Dollar Spot Epidemics Occurring on a Mixed Sward of Creeping Bentgrass and Annual Bluegrass

“…3). Our data agree with others who have shown the late-season phase of the epidemic is most damaging to a turf area (Fenstermacher, 1980;Smith et al, 1989;Powell and Vargas, 2001;Vargas, 2005). Dollar spot incidence declined during July, presumably because of hotter and more humid conditions that were less conducive for disease development.…”

“…The predominant grasses found on golf course putting surfaces are creeping bentgrass and annual bluegrass. Powell and Vargas (2001) showed seasonal variation in the vegetative compatibility groups (VCGs) of S. homoeocarpa present in a turf area. Creeping bentgrass is a synthetic cultivar, meaning that each seed is genetically distinct, and results in a range of variation in susceptibility and resistance to dollar spot even within a particular cultivar.…”

“…Site-specifi c application allows more judicious use of fungicides, but the spatial heterogeneity of dollar spot incidence has been unknown. Other genetic diversity studies show S. homoeocarpa as a predominantly clonal pathogen (Raina et al, 1997;Powell and Vargas, 2001;Viji et al, 2004). Dollar spot foci were manually counted every 2 to 3 d in 200 quadrats in 2000, and in 888 quadrats in 2001 and 2002.…”

“…Hsiang and Mahuku (1998) reported that a S. homoeocarpa population from Ontario exhibited random amplifi cation of polymorphic DNA (RAPD) and intergenic spacer-restriction fragment length polymorphism (IGS-RFLP) fi ngerprints that were in linkage disequilibrium indicating genetic recombination, but no fruiting bodies or spores were observed in their study. Other genetic diversity studies show S. homoeocarpa as a predominantly clonal pathogen (Raina et al, 1997;Powell and Vargas, 2001;Viji et al, 2004). Little research exists on inoculum sources, but a few reports contend that stromatized, infected tissue is the primary inoculum source for S. homoeocarpa (Fenstermacher, 1980;Smith et al, 1989;Vargas, 2005).…”

Response of Bentgrass Cultivars to Sclerotinia homoeocarpa Isolates Representing 10 Vegetative Compatibility Groups

“…Using RAPD-PCR Twenty-three isolates of S. homoeocarpa representing 11 VCGs were provided by Dr. Jon Powell, University of Minnesota (Table 1). These isolates were collected from sites in northern Illinois, Michigan, Arkansas, Florida, and Minnesota from 1995 to 2001 (Bernick, 2002;Powell and Vargas, 2001). The VCGs were determined by Dr. Powell's group based on the ability of the hyphae of two fungal isolates to fuse and form a stable heterokaryon (Powell and Vargas, 2001).…”