| Most diseases of turfgrass are caused by fungal and oomycete pathogens. My dissertation research focused on assessing fungicide sensitivities within Sclerotinia homoeocarpa (causal agent of dollar spot) and the genetics of Pyricularia grisea (causal agent of gray leaf spot) resistance in St. Augustinegrass (Stenotaphrum secundatum). Dollar spot is the most common and chronic disease on turfgrass and managing dollar spot on intensively cultivated turfgrass relies on the judicious use of fungicides. As with other intensively managed diseases, the heavy use of fungicides has led to the development of insensitive S. homoeocarpa to several classes of fungicides including benzimidazoles, demethylation inhibitors and dicarboximides. In vitro fungicide sensitivity assays using single discriminatory concentrations of thiophanate-methyl, propiconazole and iprodione for evaluating field efficacy of these fungicides were developed in this study and the prevalence of fungicide insensitivity within S. homoeocarpa isolated from golf courses throughout Ohio was determined.; When used to screen 192 S. homoeocarpa isolates from 55 golf courses throughout Ohio, the in vitro assays revealed that S. homoeocarpa isolates from 34, 18 and 1 golf courses are in vitro insensitive to thiophanate-methyl, propiconazole and iprodione, respectively.; P. grisea (teleomorph = Magnaporthe grisea) causes blast on rice (Oryza sativa) and gray leaf spot on turfgrass. In the continent US, gray leaf spot is a chronic disease on St. Augustinegrass in the Gulf Coast and southern California. Virulence assays performed in this study revealed that several P. grisea isolates collected from rice could also cause gray leaf spot on St. Augustinegrass and tall fescue. One rice isolate, Che86061, caused similar reactions on both resistant and susceptible cultivars of rice and St. Augustinegrass. To determine whether similar genetic mechanisms are involved in mediating the P. grisea-resistance in these two hosts, a P. grisea-infected rice expressed sequence tag (EST) library was screened using cDNA from St. Augustinegrass that had been inoculated with P. grisea as a probe. Reverse northern and web-based virtual northern approaches were used to identify 30 rice ESTs that might either induced or suppressed in St. Augustinegrass and rice following P. grisea infection. (Abstract shortened by UMI.)... |
