Duration: 10/01/2012 to 09/30/2017

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Dollar spot, caused by the fungus Sclerotinia homoeocarpa, is the most common and important turfgrass disease worldwide. This pathogen infects all grass species that are grown for turf and develops across a broad range of climatic conditions. In the United States, 42% of turfgrass managers list dollar spot as their primary disease problem, and approximately 35% of fungicides applied to turf are for control of this disease.

The dollar spot pathogen initially infects the leaves of turfgrass plants, causing severe blighting of the foliage in discrete infection centers up to 6 inches in diameter. Over time and under ideal environmental conditions, infection progresses into the plant's crown and causes death, leaving a sunken depression in the turf stand that detracts from the playability and/or aesthetic value of the affected turf. In many areas of the U.S., weather conditions can be favorable for dollar spot development throughout the entire growing season. During periods of intense disease activity, stands of susceptible turf can be severely damaged in a short period of time.

Despite the global significance of dollar spot, relatively little is known about the basic biology and ecology of S. homoeocarpa and its interactions with turfgrass hosts. Researchers are just starting to understand some of the most fundamental aspects of this pathosystem, such as the correct taxonomic placement for the pathogen and how the pathogen initiates infection within the turf host. If we are to develop and implement integrated pest management strategies, advances in our understanding of the basic biology, ecology and epidemiology of the dollar spot pathosystem are needed.

Due to our lack of knowledge about the dollar spot system, it is impossible to develop management plans that are truly integrated. Most turfgrass managers rely solely on chemical approaches to manage the disease, applying fungicides every 14 to 21 days when disease activity is observed. This approach is not sustainable from biological, economical, environmental standpoints. First, from a biological standpoint, S. homoeocarpa develops resistance to fungicides very quickly and over-reliance on chemical control has led to widespread resistance in pathogen populations. Second, from an economic standpoint, the turfgrass industry has been severely affected by the economic downturn and many facilities can no longer afford chemically-based strategies for dollar spot control. Finally, from an environmental standpoint the chemical options for control of dollar spot are dwindling rapidly due to environmental concerns and increasing federal/state/local regulations.

These challenges have led to renewed interest in research of the dollar spot pathosystem. The group of scientists currently working on dollar spot come from a diversity of backgrounds, including plant breeding, biological control, genomics, epidemiology, disease forecasting, economics, population biology, turfgrass management, molecular plant-microbe interactions, and fungicide resistance. The goal of this regional project is to provide a forum for exchange of ideas among this diverse group of scientists and encourage multi-disciplinary research that would not be possible within a single institution. This will accelerate advances in our understanding of the dollar spot pathosystem and assist in development of integrated programs for management of the most important turfgrass disease worldwide.

Objectives

Procedures and Activities

1. Elucidate key steps in the dollar spot disease cycle

Effective disease management relies on an understanding of the disease cycle so that management practices can be targeted toward key steps in the cycle. Field, growth chamber, and laboratory research will be conducted to clarify several unknowns in the dollar spot disease cycle. A real-time PCR method for detection and quantification of S. homoeocarpa in the turf stand and soil will be developed. This method will be applied in the field to study pathogen survival and sources of initial and secondary inoculum. This method will also be used to quantify initial and secondary inoculum densities and study how these relate to epidemic severity. Geospatial approaches will be employed to study spatial aspects of dollar spot development and make inferences on mechanisms of dispersal employed by S. homoeocarpa.

2. Determine the influence of environmental factors on Sclerotinia homoeocarpa growth and dollar spot development

Field observations of dollar spot development will be compared to local environmental data to determine the weather parameters that are most influential to initiation and progress of epidemics. Growth chamber research will be conducted as needed to clarify the influence of certain parameters or more accurately define key thresholds. Using this information, a weather-based dollar spot advisory will be developed to assist turfgrass managers in timing fungicide applications. The advisory system will be tested across a range of climates and turfgrass species and modified as needed to increase its accuracy. Field studies will compare advisory-based, calendar-based, and disease activity-based fungicide programs to determine the most effective and efficient method for timing applications.

3. Characterize the structure and dynamics of Sclerotinia homoeocarpa populations

A robust set of genetic and phenotypic tools will be developed for use in studies of population structure. Microsatellite loci that express length variation in sample populations will be developed into a set of markers for high-throughput population analyses. The loci that govern mating type will be characterized from genome sequence data and a PCR-based assay will be developed for rapid mating type determination in populations. A nit mutant assay for determining vegetative compatibility groups in S. homoeocarpa has already been developed (Jo et al, 2008).

Once these tools have been developed and validated, they will be applied to S. homoeocarpa populations at varying scales to answer important questions about their structure and dynamics. Global sample populations will be analyzed to determine the relative influence of host-specificity, recombination, gene flow, genetic drift, and other evolutionary forces. Locally, these methods will be used to investigate the response of S. homoeocarpa populations to fungicide programs with the goal of understanding the evolution of fungicide resistance. This work will be complemented by research of the genetic mechanisms that confer fungicide resistance and development of molecular markers to detect and quantify resistance in pathogen populations.

Genetic recombination, either through sexual or parasexual processes, is a key determinant of fungal population structure and has major implications in deployment of resistant varieties and development of fungicide resistance. In cases where evidence of genetic recombination is detected in population data, more detailed investigations will be conducted to determine if this recombination was most likely through sexual or parasexual means. Continued efforts will be made to induce sexual reproduction of S. homoeocarpa in vitro. While not a specific objective of this project, discovery and characterization of the sexual stage may resolve much of the taxonomic uncertainty related to this fungus and lead to adoption of a new Latin binomial.

4. Elucidate pathogenicity mechanisms employed by Sclerotinia homoeocarpa and identify mechanisms that confer resistance

Research of the genetic and metabolic interactions between hosts and pathogens can reveal potential targets for disease management, either through stimulation of host defense responses or suppression of key pathogenicity factors in the pathogen. Gene expression during interactions between S. homoeocarpa and hosts with varying susceptibility levels will be analyzed in an effort to identify potential targets for disease management. Metabolomic analyses will also be employed to search for key host or pathogen metabolites that influence the outcome of interactions.

Recent research suggests that there is host specificity or strong host preference of S. homoeocarpa isolates toward cool- or warm-season grasses. Growth chamber inoculations will be performed to measure the degree of specificity or preference that exists among isolates. Depending on the results of these inoculations, expression analysis of different combinations of pathogen isolates and host species may be employed to pinpoint key host or pathogen genes that regulate the observed specificity or preference.

It was recently discovered that S. homoeocarpa is pathogenic toward Arabidopsis thaliana in the growth chamber. This presents the opportunity to investigate genetic and phenotypic responses of model plants to S. homoeocarpa.

Certain bentgrass species, like velvet bentgrass, and newly developed cultivars of creeping bentgrass have improved tolerance or resistance to dollar spot compared to traditional creeping bentgrass cultivars. This resistance needs to be characterized and the components of resistance and how it is inherited need to be determined.

5. Refine cultural control practices with the goal of reducing fungicide inputs

Field research will be conducted to evaluate non-chemical methods for dollar spot management. Creeping bentgrass cultivars with improved dollar spot resistance were recently released into the turfgrass market. Field research will compare the fungicide inputs necessary to provide acceptable dollar spot control on resistant and susceptible varieties. Such an analysis can help turfgrass managers to decide if it is economically feasible to undergo a costly conversion process. Lightweight rolling, a routine practice on golf course putting greens, was recently shown to suppress dollar spot development in Michigan. Continued field research will aim to determine the mechanism(s) by which rolling suppresses disease development and closely define the parameters under which this benefit is achieved.

The duration of nighttime leaf wetness has a major influence on dollar spot development, and early morning dew removal is known to provide partial suppression of the disease. However, the influence of soil moisture on dollar spot development remains poorly understood. Field research is planned to determine the influence of irrigation frequency and amount on dollar spot development in resistant and susceptible cultivars of creeping bentgrass.

A variety of biological fungicides and plant health promoters have or will soon be released into the turfgrass market. The activity of these products against dollar spot and their potential to reduce synthetic fungicide inputs will be investigated in the field, growth chamber, or laboratory as appropriate.

6. Refine chemical control practices with the goal of reducing fungicide inputs

Recent research indicates that early spring fungicide applications can significantly delay dollar spot epidemic development. Further research is needed to determine if early spring applications are effective across multiple environments and growing seasons and if their implementation can consistently reduce overall fungicide inputs. Taking advantage of results generated through Objectives 1 and 2, the timing, method, and product selection will be refined so that turfgrass managers can obtain maximum benefit from these early preventive applications.

Other techniques that may improve the performance of fungicides or extend their efficacy, such as pre-application mowing or dew removal, nozzle selection, spray dilution rate, and spray adjuvants, will be tested alone and in combination in order to develop best practices for maximizing the performance of fungicide applications and reducing overall fungicide inputs.

Expected Outcomes and Impacts

Projected Participation

View Appendix E: Participation

Educational Plan

Applied scientists, extension specialists, and turfgrass managers will be the primary beneficiaries of the information generated through this multi-disciplinary regional project. Product manufacturers and sales distributors are secondary audiences. Individuals or groups of project participants will publish their research results in appropriate peer-reviewed journals and may also publish their work in trade journals when appropriate. A project website will be developed and maintained to catalog publications relevant to this project and to highlight recent advances. Upon conclusion of the project, an article or series of articles that summarize results from the entire project will be prepared for publication in Golf Course Management or similar high-impact trade journal. Webinars or other internet-based communication methods will also be used to disseminate research results and new management strategies to end-users at the conclusion of the project or earlier if sufficient progress is made.

Organization/Governance

The recommended Standard Governance for multistate research activities include the election of a Chair, a Chair-elect, and a Secretary. To provide continuity of governance, the outgoing Secretary will become Chair-elect and the outgoing Chair-elect will become Chair at the conclusion of the annual meeting. At that time, nominations will be taken for the position of Secretary and an election will held by secret ballot. The Chair will have primary responsibility for organization of an annual meeting at a time and place that is agreed upon by project participants. The Chair-elect will assist the Chair with organization and conduct of the meeting. The Secretary will be responsible for keeping meeting minutes and submission of the annual report. Administrative guidance will be provided by an assigned Administrative Advisor and a CSREES Representative.

Literature Cited

Bonos S.A. (2006) Heritability of dollar spot resistance in creeping bentgrass. Phytopathology 96:808-812.

Bonos S.A., Clarke B.B., Meyer W.A. (2006) Breeding for disease resistance in the major cool-season turfgrasses. Annual Review of Phytopathology 44:213-234. DOI: 10.1146/44.070505.14338.

Burpee L.L. (1997) Control of dollar spot of creeping bentgrass caused by an isolate of ,Sclerotinia homoeocarpa resistant to benzimidazole and demethylation-inhibitor fungicides. Plant Disease 81:1259-1263.

Burpee L.L., Goulty L.G. (1986) Evaluation of two dollar spot forecasting systems for creeping bentgrass. Canadian Journal of Plant Science 66:345-351.

Burpee L.L., Green D.E., Stephens S.L. (1996) Interactive effects of plant growth regulators and fungicides on epidemics of dollar spot in creeping bentgrass. Plant Disease 80:1245-1250.

Chakraborty N., Chang T., Casler M.D., Jung G. (2006) Response of bentgrass cultivars to Sclerotinia homoeocarpa isolates representing 10 vegetative compatibility groups. Crop Science 46:1237-1244.

Detweiler A.R., Vargas J.M., Danneberger T.K. (1983) Resistance of Sclerotinia homoeocarpa to iprodione and benomyl. Plant Disease 67:627-630.

DeVries R.E., Trigiano R.N., Windham M.T., Windham A.S., Sorochan J.C., Rinehart T.A., Vargas J.M. (2008) Genetic analysis of fungicide-resistant Sclerotinia homoeocarpa isolates from Tennessee and northern Mississippi. Plant Disease 92:83-90.

Dunn J.H., Minner D.D., Fresenburg B.F., Bughrara S.S. (1996) Clippings disposal and fertilization influence disease in perennial ryegrass turf. Hortscience 31:1180-1181.

Fidanza M.A., Wetzel H.C., Agnew M.L., Kaminski J.E. (2006) Evaluation of fungicide and plant growth regulator tank-mix programmes on dollar spot severity of creeping bentgrass. Crop Protection 25:1032-1038.

Golembiewski R.C., Vargas J.M., Jones A.L., Detweiler A.R. (1995) Detection of demethylation inhibitor (DMI) resistance in Sclerotinia homoeocarpa populations. Plant Disease 79:491-493.

Hall R. (1984) Relationship between weather factors and dollar spot of creeping bentgrass. Canadian Journal of Plant Science 64:167-174.

Horvath B.J., Kravchenko A.N., Robertson G.P., Vargas J.M. (2007) Geostatistical analysis of dollar spot epidemics occurring on a mixed sward of creeping bentgrass and annual bluegrass. Crop Science 47:1206-1216.

Hsiang T., Yang L., Barton W. (1997) Baseline sensitivity and cross-resistance to demethylation-inhibiting fungicides in Ontario isolates of Sclerotinia homoeocarpa. European Journal of Plant Pathology 103:409-416.

Hsiang T., Yang L., Barton W. (1998) Relative virulence of isolates of Sclerotinia homoeocarpa with varying sensitivity to propiconazole. European Journal of Plant Pathology 104:163-169.

Jo Y., Boehm M., Jung G. (2007) Rapid population shift of Sclerotinia homoeocarpa in response to fungicide applications on turfgrass. Phytopathology 97:S53-S53.

Jo Y.-K., Chang S.W., Rees J., Jung G. (2008) Reassessment of vegetative compatibility of Sclerotinia homoeocarpa using nitrate-nonutilizing mutants. Plant Disease 98:108-114.

Latin R. (2006) Residual efficacy of fungicides for control of dollar spot on creeping bentgrass. Plant Disease 90:571-575.

Lee J., Fry J., Tisserat N. (2003) Dollar spot in four bentgrass cultivars as affected by acibenzolar-s-methyl and organic fertilizers. Plant Health Progress. doi:10.1094/PHP-2003-0626-01-RS.

Liu L.X., Hsiang T., Carey K., Eggens J.L. (1995) Microbial populations and suppression of dollar spot disease in creeping bentgrass with inorganic and organic amendments. Plant Disease 79:144-147.

McDonald S.J., Dernoeden P.H., Bigelow C.A. (2006) Dollar spot and gray leaf spot severity as influenced by irrigation, chlorothalonil, paclobutrazol, and a wetting agent. Crop Science 46:2675-2684. DOI: 10.2135/cropsci.12.0495.

Mitkowski N.A., Colucci S. (2006) The identification of a limited number of vegetative compatibility groups within isolates of Sclerotinia homoeocarpa infecting Poa spp. and Agrostis palustris from temperate climates. Journal of Phytopathology 154:500-503.

Nelson E.B., Craft C.M. (1992) Suppression of dollar spot on creeping bentgrass and annual bluegrass turf with compost-amended topdressings. Plant Disease 76:954-958.

Uriarte R.F., Shew H.D., Bowman D.C. (2004) Effect of soluble silica on brown patch and dollar spot of creeping bentgrass. Journal of Plant Nutrition 27:325-339. DOI: 10.1081/pln-120027657.

Viji G., Uddin W., O'Neill N.R., Mischke S., Saunders J.A. (2004) Genetic diversity of Sclerotinia homoeocarpa isolates from turfgrasses from various regions in North America. Plant Disease 88:1269-1276.

Vincelli P., Doney J.C., Jr., Powell A.J. (1997) Variation among creeping bentgrass cultivars in recovery from epidemics of dollar spot. Plant Disease 81:99-102.

Attachments

Land Grant Participating States/Institutions

KS, MA, MI, MS, NC, ND, NJ, NY, TX

Non Land Grant Participating States/Institutions