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Management of Dollar Spot and Gray Leaf Spot on Turfgrass

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Management of Dollar Spot and Gray Leaf Spot on Turfgrass MANAGEMENT OF DOLLAR SPOT AND GRAY LEAF SPOT ON TURFGRASS DISSERTATION Presented in Partial Fulfillment of the Requirements of the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Young Ki Jo, M.S. * * * * * The Ohio State University 2005 Dissertation Committee: Approved by Dr. Michael J. Boehm, Advisor Dr. Margaret G. Redinbaugh Advisor Dr. Guo-Liang Wang Graduate Program of Plant Pathology Dr. David S. Gardner ABSTRACT 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. Discriminatory concentrations for these fungicide were determined to be: thiophanate- methyl = 1,000 µg a.i. ml-1; propiconazole = 0.1 µg a.i. ml-1; and iprodione = 1.0 µg a.i. -1 ml . Effective concentration of 50% inhibition (EC50) was estimated based on relative mycelial growth of S. homoeocarpa on potato dextrose agar (PDA) versus PDA amended with the discriminatory concentration of each fungicide. Field trials conducted at three locations in 2002 and ten locations in 2003 revealed that the in vitro assays predicted ii accurately field efficacy for thiophanate-methyl. Reduced in vitro fungicide sensitivity to propiconazole and iprodione detected in this study provided valuable insights regarding the potential development of inefficacy of these two fungicides in the field. 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. In recent years, outbreaks of gray leaf spot have resulted in extensive damage on perennial ryegrass (Lolium multiflorum) and tall fescue (Festuca arundincea) in the midwestern and northeastern United States. 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. These ESTs were classified into six putative function groups according to the NCBI database of Clusters of Orthologous Groups of proteins (COGs). Northern blot analysis confirmed that expression of seven ESTs assigned to different function groups iii was similar in both rice and St. Augustinegrass and indicated that some similar genes are involved in these two graminaceous hosts. iv Dedicated to Chookyung Jo (조추경) and Youngsun Chun (전영선) v ACKNOWLEDGMENTS I wish to thank Mike Boehm for intellectual and financial support, encouragement and motivation to make this dissertation possible, and for providing diverse opportunities to extend my vision and knowledge toward the scientific world, academic professionalism and human relations. I cannot thank enough for Joe Rimelspach for sharing his experience and knowledge about turfgrass disease diagnosis and outreach extension. I thank Guo-Liang Wang for providing lab space and chemicals to accomplish the gray leaf spot project, and for guiding my experiment with regular-based discussions. I am grateful to Peg Redinbaugh and Dave Gardner for critically discussing with me various aspects of experiment and this dissertation. Finally, I should give a special thank to Rachel for standing by my side, halving difficulty and doubling happiness. vi VITA December 24, 1970…………………. Born in Sachun city, Republic of Korea 1996…………………………………. B.S. Biology Education, Seoul National University, Republic of Korea 2000…………………………………. M.S. Entomology, Michigan State University 2001 – present ……………………… Graduate Associate, The Ohio State University PUBLICATIONS 1. Jo, Y., Rimelspach, J. W., and Boehm, M. J. 2005. OSU Extension Factsheet HYG- 3084-05 entitled “Brown Patch on Turfgrass.” (Available online at: http://ohioline.osu.edu/hyg-fact/3000/3084.html / verified June 2005). 2. Jo, Y., Rimelspach, J. W., and Boehm, M. J. 2004. OSU Extension Factsheet HYG- 3083-04 entitled “Gray Leaf Spot on Turfgrass.” (Available online at: http://ohioline.osu.edu/hyg-fact/3000/3083.html / verified June 2005). 3. Jo, Y., Rimelspach, J. W., and Boehm, M.J. 2004. OSU Extension Factsheet HYG- 3082-04 entitled “Summer Patch on Turfgrass.” (Available online at: http://ohioline.osu.edu/hyg-fact/3000/3082.html / verified June 2005). vii 4. Jo. Y, Smitley, D. R., Predation of Ataenius spretulus (Coleoptera: Scarabaeidae) eggs and grubs by species of Carabidae and Staphylinidae on golf courses in Michigan, December 2003. Environmental Entomology Vol. 32, No. 6, p. 1370-1376. 5. Rimelspach, J. W., Boehm, M. J., Hicks, T. E., Thomas, S. L., and Jo, Y. 2003. Evaluation of fungicides for the control of brown patch in creeping bentgrass, 2001. Fungicide and Nematicide Tests 58:T023. 6. Cappaert, D. L., Smitley, D. R., and Jo, Y. 2002. Entomopathogenic nematodes and Hypoaspis mites, biocontrols of fungus gnats and shoreflies, 1999. Arthropod Management Tests 27:G2. FIELDS OF STUDY Major Field: Plant Pathology Area of Concentration: Turfgrass Pathology viii TABLE OF CONTNENTS Page Dedication………………………………………………………………………….…….v Acknowledgements……………………………………………………………….……..vi Vita……………………………………………………………………………….……..vii List of Tables……………………………………………………………………………xi List of Figures…………………………………………………………………….…….xii Chapter 1. Introduction………………………………………………………………….1 Chapter 2. Literature review………………………………………………………...…..4 Chapter 3. Fungicide Sensitivity of Sclerotinia homoeocarpa Isolates from Golf Courses in Ohio Introduction ………………………………………………………………………...21 Materials and Methods…………….…………………………………….……….…24 Results ……………………………………………………………………………...29 Discussion ………………………………………………………………………….33 Chapter 4. Expression Analysis of Rice Defense-related Genes In Turfgrass In the Response to Gray Leaf Spot Introduction ………………………………………………………………………...56 Materials and Methods…………….…………………………………………...…...58 Results ………………………………………………………………………...……65 ix Discussion ……………………………………………………………………….…69 Chapter 5. Conclusions…………………………………………………………………91 Appendix A. Recipe of Oatmeal Agar Media for Pyricularia grisea ………….……...93 Bibliography…………………………………………………………………………….95 x LIST OF TABLES Table Page 3.1 Sclerotinia homoeocarpa isolates used in this study……………………..……......39 3.2 Efficacy of thiophanate-methyl, propiconazole and iprodione on dollar spot severity at three locations in 2002………………………………………….……...43 3.3 Efficacy of thiophanate-methyl, propiconazole and iprodione on dollar spot severity at 10 locations in 2003……..……………………………………………..44 3.4 In vitro fungicide sensitivities (EC50(D)) of 10 S. homoeocarpa isolates collected from each field location in August 2003………………………..46 3.5 Fungicide sensitivities of S. homoeocarpa isolates collected from golf courses in Ohio between 1999 and 2004…………………………………………………...48 4.1 Virulence of Pyricularia grisea isolates used in this study……….….…………....74 4.2 Expression levels of expressed sequence tags (ESTs) identified in this study..…...76 xi LIST OF FIGURES Figure Page 2.1 Symptom of dollar spot on creeping bentgrass (Agrostis stolonifera L.)…….…....12 2.2 Hourglass-shaped lesions of dollar spot extending across the entire leaf blade of creeping bent grass…………………...……………………………..……...…...13 2.3 Symptom of gray leaf spot on perennial ryegrass (Lolium perenne L.)…………...20 3.1 Location of golf courses in Ohio from which Sclerotinia homoeocarpa was collected and where fungicide efficacy tests were conducted……………………..50 3.2 Relationship between EC50 values and relative mycelial growth of S. homoeocarpa on PDA amended with single discriminatory concentrations of thiophanate-methyl, propiconazole and iprodione…………………………….….51 3.3 Relationship between EC50 values and EC50(D) values for thiophanate-methyl, propiconazole and iprodione……………….…….……………………….………52 3.4 Relationship between mean EC50(D)
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