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Management of dollar spot and gray leaf spot on turfgrass
Jo, Young Ki

2005, Doctor of Philosophy, Ohio State University, Plant Pathology.
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 genetics of Pyricularia grisea (causal agent of gray leaf spot)-resistance in St. Augustinegrass. As with other intensively managed diseases, the heavy use of fungicides has led to the development of resistance in S. homoeocarpa to several classes of fungicides. The goal of my work was to develop in vitro fungicide sensitivity assays using single discriminatory concentrations for thiophanate-methyl, propiconazole and iprodione and to use these assays to determine the prevalence of fungicide insensitivities within S. homoeocarpa isolates recovered from golf courses throughout Ohio. Discriminatory concentrations for these fungicides were determined as thiophanate-methyl = 500 ug a.i./ml; propiconazole = 0.1 ug a.i./ml; and iprodione = 1 ug a.i./ml. Replicated field trials correlating results of in vitro assays with fungicide efficacy in the field were conducted in 2002 and 2003. When used to screen 192 S. homoeocarpa isolates from 55 golf courses throughout Ohio, the in vitro assays revealed that thiophanate-methyl and propiconazole insensitivity was prevalent (34 and 18 golf courses, respectively). The prevalence of iprodione insensitivity in S. homoeocarpa was low (1/55 golf courses). P. grisea causes blast in rice and gray leaf spot in turfgrass. Virulence assays performed in this study revealed that some P. grisea isolates collected from rice could also infect 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 P. grisea -infected St. Augustinegrass. Reverse northern, web-based virtual northern and northern (RNA blot) approaches were used to identify 30 rice ESTs that were either induced or suppressed in St. Augustinegrass following infection by P. grisea . These ESTs were classified into six different putative function groups according to the NCBI database of Clusters of Orthologous Groups of proteins (COGs) and potentially involved in P. grisea -resistance in these two graminaceous hosts.
Michael Boehm (Advisor)
118 p.

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