Response of bentgrass cultivars to Sclerotinia homoeocarpa isolates representing 10 vegetative compatibility groups

Dollar spot caused by Sclerotinia homoeocarpa F.T. Bennett is a major disease of turfgrass throughout the world. Current control strategies depend heavily on fungicide application. Host resistance is an alternate management strategy, but a thorough understanding of the pathogen and host interaction is required to utilize it successfully. Seventy-nine clones of 10 cultivars of creeping (A. stolonifera L.), colonial (A. capillaris L.), dryland (A. castellana Boiss. & Reut.), and velvet (A. canina L.) bentgrass species were inoculated with an isolate of S. homoeocarpa in the greenhouse. A large degree of genetic variation in response to S. homoeocarpa at the species, cultivar, and clone levels was detected. In addition, 18 isolates of S. homoeocarpa representing 10 vegetative compatibility groups (VCGs) were used to inoculate 12 bentgrass cultivars. Disease severity evaluations showed significant difference among bentgrass cultivars and species in their response to dollar spot. The colonial and velvet bentgrass cultivars were significantly less susceptible to all the isolates of S. homoeocarpa compared to the creeping bentgrass cultivars. The isolates of S. homoeocarpa showed significant differences in levels of aggressiveness. However, data from pathogenicity tests indicated a lack of race-specific interactions. Therefore, turfgrass breeders should be able to select for resistance to one or a few highly virulent isolates of the pathogen, and obtain resistance to a wide array of isolates.