Research
Dollar Spot (Sclerotinia homoeocarpa)
In vitro Assessment of Sclerotinia homoeocarpa Resistance to Fungicides and Plant Growth Regulators
Chang Ho Ok, James Popko, Katie Campbell-Nelson, and Geunhwa Jung
Dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) is the most economically important turfgrass disease in North America. This disease is primarily controlled by fungicide application on golf courses; however, fungicide resistance has been confirmed in three of the five fungicide classes commonly used to control dollar spot. The main objective of this study was to evaluate S. homoeocarpa resistance to multiple fungicide classes and cross-resistance among active ingredients of the same class. Sixty-four isolates were randomly selected from four unique geographic locations and assayed for in vitro fungicide sensitivity to six demethylation inhibitor (DMI) fungicides, two dicarboximide fungicides, one anilene fungicide, one benzimidazole fungicide and three type II plant growth regulators. A series of concentrations for each active ingredient were used to determine the EC50 values providing correlation coefficients for all active ingredients. All active ingredients from the DMI class were highly correlated (P < 0.0001) to each other as well as to the dicarboximide (iprodione) and plant growth regulators (flurprimidol and paclobutrazol). Isolates resistant to thiophanate-methyl had significantly higher EC50 values than isolates sensitive to thiophanate-methyl for all active ingredients except for boscalid. Findings show that multiple class and cross-resistance has developed in S. homoeocarpa and that plant growth regulators have a fungistatic effect on S. homoeocarpa similar to that of demethylation inhibitor fungicides. The high correlation of in vitro sensitivities among PGRs and DMI fungicides further suggests that plant growth regulators can contribute to the selection of DMI resistant isolates or facilitate decreased sensitivity to demethylation inhibitor fungicides.The effect of demethylation inhibitor fungicides on Sclerotinia homoeocarpa populations
James Popko, Chang Ho Ok, Katie Campbell-Nelson, and Geunhwa Jung
The objective of this project was to investigate the effect of propiconazole (DMI) rates on changes in S. homoeocarpa populations using in-vitro fungicide assays and field efficacy tests. Sclerotinia homoeocarpa samples were collected from nine golf courses in MA and CT in 2009 and asssayed for DMI insensitivity. Results indicate that each golf course has S. homoeocarpa populations with differing levels of DMI sensitivity depending on cultural management and history of fungicide uses at that site. Reduced field efficacy of propiconazole was observed at sites with preexisting DMI insensitivity, whereas complete control was observed at sites with no previous DMI exposure. This study was replicated in 2009 and 2010 to confirm the existence of site-specific population structures and to study how the structures have changed after two years of DMI applications at different rates and intervals.
This research has directly contributed to the formation of a Fungicide Resistance Assay extension service for superintendants and home lawn owners with difficulties controlling dollar spot. The assay is conducted at the UMASS Turf Pathology lab using all commonly used fungicide classes to test levels of fungicide resistance to each. Results of the assay give clients a holistic understanding of their dollar spot populations along with effective cultural and chemical control options saving some thousands of dollars in misapplications of chemicals to dollar spot populations with fungicide resistance.
Reverting DMI-resistant dollar spot populations with the use of non-DMI fungicides
Geunhwa Jung
Various fungicides: (boscalid, Emerald®; chlorothalonil, Daconil Ultrex®; iprodione, Chipco 26GT® and Ipro SE®; vinclozolin, Curalan®; and more) are being tested for efficacy on a DMI-resistant dollar spot population at a golf course in Cape Cod. The objective of this experiment which began in 2007 is to identify non-DMI fungicides capable of reverting DMI-resistant populations back to sensitive populations so that the DMI fungicides can be used again. This experiment is also examining the length of reversion time while maintaining acceptable turf quality. Based on three years’ careful monitoring of the populations using laboratory assays and evaluating field control, we have not observed any significant shift of the resistant populations.
Effect of repeat, rotation, or mixed applications of fungicides on dollar spot resistance development
Geunhwa Jung
Repeat applications of fungicides with the same chemistry are known to lead to fungicide resistance. The objective of this project is to determine the effect of repeat applications of the same fungicide chemistry, and to determine the effect
of rotation or tank-mix between fungicide chemistries on resistance development in a sensitive dollar spot population over several years. Treatments include: repeat applications of propiconazole (DMI), repeat applications of thiophanate methyl (TM), a rotation between DMI and TM, and a rotation including a mixture of DMI + TM and TM alone. The plot includes 4 replications of 3 x 6 ft plots per treatment, and each treatment is applied 3-4 times total every 21 days during the summer. Ratings are made every 7 days including counting dollar spot infection centers, and taking pictures of each plot. Current results indicate that TM resistance is selected in as few as 2 back to back applications but will take a few years to establish, while DMI resistance has yet to be selected after 2 years of 3 repeat applications per year on a sensitive population. Rotation between DMI and TM alone did not select TM resistant dollar spot isolates as fast as rotation between DMI+TM tank mixed and TM alone. The project will continue in its 3rd season in 2010 to determine whether or not DMI resistance can be selected from the sensitive population.
Determining molecular mechanisms responsible for DMI resistance in dollar spot
Jon Hulvey and Geunhwa Jung
Demethylation Inhibitor (DMI) fungicides have been widely used in agriculture and turf since their release early in the 1980s. The single site mode of action of DMIs has resulted in increased levels of resistance in many target organisms including fungi. In the Jung lab we are investigating the mechanism of DMI fungicide insensitivity in Sclerotinia homoeocarpa using techniques in molecular biology, genomics, and bioinformatics. Over the past 3 years, we have maintained experimental plots at several New England golf courses and the UMASS Joseph Troll Turf Research Facility to better understand population dynamics of this pathogen in response to DMI fungicide applications. Fungal isolates taken from these populations before and after DMI application are being used to research the mechanisms of DMI fungicide insensitivity. We are utilizing Next Generation Sequencing, quantitative RT-PCR, and genotyping methods to better understand how this pathogen is able to overcome fungicide pressures. The goal of this research is to understand how S. homoeocarpa populations respond to propiconazole application pressure at a genetic level which have implications for resistance management strategies.
Evaluation of the New England Velvet Bentgrass Collection
Loreto Araneda, and Geunhwa Jung, University of Massachusetts and Rebecca Nelson Brown and Cynthia Percivalle, University of Rhode Island
This is a USGA funded project with the objectives of collecting velvet bentgrass (Agrostis canina L.) germplasm, identify and group accessions based on their genetic similarities for analysis and breeding, and to evaluate accessions for improved resistance to biotic and abiotic stresses. All 250 accessions collected from old golf courses throughout New England were evaluated for salt tolerance, turf color, growth rate, and dollar spot susceptibility at the University of Rohde Island. At the University of Massachusetts, a flow cytometry analysis was carried out to clarify the ploidy level of the accessions. 74% (159 individuals) of the accessions were found to be diploid with velvet phenotypes and 26% (56 individuals) were found to be tetraploid with creeping bentgrass phenotypes, however, three of them were neither velvet or creeping bentgrass. Significant progress has been made to identify germplasm with enhanced resistance to biotic and abiotic stresses.
Polyploid Breeding Method for Improvement of Bentgrass
Geunhwa Jung
Of the 200 Agrostis spp., three bentgrass species (allotetraploid creeping, allotetraploid colonial, and diploid velvet) have been used on golf courses. Of them, creeping bentgrass is the most commonly used due to low mowing tolerance and proliferous stolon production. Due to its susceptibility to dollar spot (caused by Sclerotinia homoeocarpa) and snow molds (caused by Typhula blight and Microdochium nivale), fungicides are extensively used on golf courses. Breeding for improvement of disease resistance is an essential part of integrated pest management. However, due to low seed yield and sterility issues of hybrids, development of new hybrid bentgrass varieties via interspecific hybridization has been unsuccessful. In this project, one clonal plant (“M56”) confirmed to be hexaploid readily crosses with either tetraploid creeping or colonial bentgrass plants without a sexual barrier to produce hybrid seeds. Hybrid plants derived from crosses are pentaploid. Therefore, M56 can be utilized for breeding as either a bridging plant for crosses between bentgrasses or as a parental plant, meaning that traits of interest from creeping bentgrass and colonial bentgrass can be naturally and sexually combined. Development of pentaploid bentgrass varieties are in progress at UMass.
Bentgrass crossing blocks were established in the fall of 2009 using the following three bentgrass clones (M56, creeping bentgrass 372, and colonial bentgrass 372.2) either in two- or three-way hybridization. Seeds from individual or combined crosses within each block will be separately harvested in the summer of 2010 and evaluation for their field performance.
Perennial Ryegrass (Lolium spp.) Breeding
QTL Mapping of Resistance to Gray Leaf Spot (GLS) in Lolium.
Geunhwa Jung
This is a USGA funded project to research the interactions between pathogen (Magnaporthe grisea) variability and host (Lolium perenne) resistance. The ultimate goal of this research is to produce perennial ryegrass plants having a broad spectrum of gray leaf spot resistance by pyramiding various resistant genes originated from different Lolium species and cultivars. Two ryegrass parent clones (MFA, MFB) and five commercial resistant cultivars (Gray Star, Gray Fox, Grey Goose, Manhattan-5, Paragon GLR) were included in the study. These gray leaf spot resistant cultivars showed only moderate resistance to the 13 geographically diverse isolates. This result may indicate non-race specific resistance in perennial ryegrass. Preliminary results also indicated a marginal significant interaction between gray leaf spot isolates and ryegrass germplasms under growth chamber conditions. Further inoculations using clonally replicated ryegrass plants and thirteen geographically diverse gray leaf spot isolates will be performed to check whether the resistance in commercial cultivars differ from MFA and MFB. DNA markers significantly associated with QTLs for GLS resistance in the various sources will be developed for marker-assisted selection.