Dollar Spot Research Articles

Divot recovery of cool‐season turfgrass species and mixtures in low maintenance fairways

AbstractThere is a need to identify turfgrass species and mixtures for golf course fairways that can be managed sustainably with reduced fertility, pesticides, and irrigation. The current study evaluated Agrostis stolonifera L. (creeping bentgrass [AST]), Agrostis capillaris L. (colonial bentgrass [ACP]), Agrostis canina L. (velvet bentgrass [ACN]), Festuca rubra L. ssp. commutata Gaudin (Chewings fescue [FRC]), Festuca brevipila Tracey (hard fescue [FBP]), and Festuca rubra L. ssp. littoralis (G. Mey) Auquier (slender creeping red fescue [FRL]) planted as monostands and in mixtures to determine the ideal choice for low maintenance fairway management. Plots were established in the fall of 2014 in a randomized complete block design with three replications. Turf quality and disease resistance were evaluated visually from 2015–2018. Divots were mechanically created during the growing seasons of 2017 and 2018 and evaluated visually for initial divot injury and recovery every two weeks. Monostands and mixtures of ACN had the best turf quality and least brown patch (caused by Rhizoctonia solani Kühn) but took longer to recover from divots. A. capillaris monostands and mixtures exhibited above average turf quality but were more susceptible to brown patch disease. Compared to all other entries, monostands and mixtures of AST had the lowest turf quality and most dollar spot (caused by Clarireedia jacksonii C. Salgado, L.A. Beirn, B.B. Clarke, & J.A. Crouch sp. nov.). Festuca L. spp. (fine fescue spp.), when mixed with improved ACP cultivars such as ‘Puritan’ and ‘Capri’, exhibited above average turf quality but had below average performance in monostands or when combined with older ACP cultivars such as SR 7100. Divot resistance and recovery were variable between years but the FRL cultivar Shoreline and most FRC cultivars recovered quickly in both years, while ACP cultivar Capri and FBP cultivar Beacon were slow to recover in both years. Most species and mixtures were comparable and, in some cases, better than AST for divot recovery indicating that the alternative species tested in this study could provide sustainable turfgrass management on golf course fairways.

Hyperlocal Variation in Soil Iron and the Rhizosphere Bacterial Community Determines Dollar Spot Development in Amenity Turfgrass.

Dollar spot, caused by the fungal pathogen Clarireedia spp., is an economically important foliar disease of amenity turfgrass in temperate climates worldwide. This disease often occurs in a highly variable manner, even on a local scale with relatively uniform environmental conditions. The objective of this study was to investigate mechanisms behind this local variation, focusing on contributions of the soil and rhizosphere microbiome. Turfgrass, rhizosphere, and bulk soil samples were collected from within a 256-m2 area of healthy turfgrass, transported to a controlled environment chamber, and inoculated with Clarireedia jacksonii Bacterial communities were profiled by targeting the 16S rRNA gene, and 16 different soil chemical properties were assessed. Despite their initial uniform appearance, the samples differentiated into highly susceptible and moderately susceptible groups following inoculation in the controlled environment chamber. The highly susceptible samples harbored a unique rhizosphere microbiome with suggestively lower relative abundance of putative antibiotic-producing bacterial taxa and higher predicted abundance of genes associated with xenobiotic biodegradation pathways. In addition, stepwise regression revealed that bulk soil iron content was the only significant soil characteristic that positively regressed with decreased dollar spot susceptibility during the peak disease development stage. These findings suggest that localized variation in soil iron induces the plant to select for a particular rhizosphere microbiome that alters the disease outcome. More broadly, further research in this area may indicate how plot-scale variability in soil properties can drive variable plant disease development through alterations in the rhizosphere microbiome.IMPORTANCE Dollar spot is the most economically important disease of amenity turfgrass, and more fungicides are applied targeting dollar spot than any other turfgrass disease. Dollar spot symptoms are small (3 to 5 cm), circular patches that develop in a highly variable manner within plot scale even under seemingly uniform conditions. The mechanism behind this variable development is unknown. This study observed that differences in dollar spot development over a 256-m2 area were associated with differences in bulk soil iron concentration and correlated with a particular rhizosphere microbiome. These findings provide interesting avenues for future research to further characterize the mechanisms behind the highly variable development of dollar spot, which may inform innovative control strategies. Additionally, these results suggest that small changes in soil properties can alter plant activity and hence the plant-associated microbial community, which has important implications for a broad array of agricultural and horticultural plant pathosystems.

Strategies for increasing ferrous sulfate efficacy against dollar spot of creeping bentgrass

AbstractDollar spot (Clarireedia spp.) is a damaging turfgrass disease. Ferrous sulfate (FeSO4) suppresses dollar spot with little risk of resistance. Optimizing FeSO4 applications is crucial for adequate dollar spot suppression. Supplementing FeSO4 applications with chlorothalonil fungicide could also increase efficacy against dollar spot and longevity of disease suppression. Four experiments were conducted to determine the 1) optimal water carrier volume for FeSO4, 2) proper nozzle selection for FeSO4 applications, 3) most efficacious rate combination of FeSO4 and chlorothalonil, and 4) longevity of chlorothalonil efficacy when applied in conjunction with FeSO4 for dollar spot suppression on creeping bentgrass (Agrostis stolonifera L.). These studies were conducted on either putting greens mown at 3.2 to 6.4 mm or fairways mown at 16.5 mm. The following carrier volumes were tested in Experiment 1: 281, 421, 842 and 1684 L ha–1. For Experiment 2, Turbo FloodJet (TF), Turbo TeeJet Induction (TTI), Air Induction Turbo TwinJet (AITTJ), and Extended Range Flat Fan (XRFF) nozzles were used to determine optimal nozzle type. In Experiment 3, chlorothalonil was applied at 0, 2.28, 4.57, 6.86 and 9.16 kg a.i. ha–1 with or without 48.8 kg ha–1 of FeSO4. In Experiment 4, 48.8 kg ha–1 of FeSO4 was applied biweekly and chlorothalonil was curatively applied at 8.2 kg a.i. ha–1 when infection centers per plot reached 30. Water carrier volume had no effect on dollar spot suppression, the AITTJ and XRFF nozzles provided the greatest disease suppression and turf quality, FeSO4 reduced effective chlorothalonil rates by up to 68.5% and FeSO4 increased longevity of chlorothalonil efficacy.

Influence of calcium and nitrogen fertilizer on creeping bentgrass infected with dollar spot under cool temperatures

AbstractDollar spot, caused by the fungal pathogen Clarireedia homoeocarpa Bennett, is a wide‐spread disease of creeping bentgrass (Agrostis stolonifera L.) that in the north central region of the U.S., occurs as early as March. Over‐dependence on fungicides has resulted in widespread resistance, necessitating non‐chemical treatment approaches. The objective of this experiment was to assess the effects of N and Ca fertilizers on creeping bentgrass for dollar spot tolerance under cool temperatures. In a chilling chamber, a single application of Ca or N fertilizer significantly reduced dollar spot disease cover by 47% or 34%, respectively, compared to the untreated control. Application of both Ca and N, however, appeared to be antagonistic and resulted in only a 14% reduction of disease cover. Application of Ca, not N, improved root production but reduced shoot growth in the 4‐week period regardless of dollar spot, resulting in an elevated root to shoot ratio. Root architecture, including total root length, surface area and total tips, was also improved following a Ca only application. Collectively, these results suggested that Ca might play a beneficial role in improving the stress tolerance of creeping bentgrass, and building healthier and stronger root systems in the spring‐like conditions. Although a single application of Ca does not adequately suppress dollar spot, future research might be of interest to explore optimal application strategies in order to reduce over‐dependence on fungicides.

Genome Resources for Seven Fungal Isolates That Cause Dollar Spot Disease in Turfgrass, Including Clarireedia jacksonii and C. monteithiana

Fungi in the genus Clarireedia are widespread and destructive pathogens of grasses worldwide, and are best known as the causal agents of dollar spot disease in turfgrass. Here, we report genome assemblies of seven Clarireedia isolates, including ex-types of the two most widespread species, Clarireedia jacksonii and C. monteithiana. These datasets provide a valuable resource for ongoing studies of the dollar spot pathogens that include population diversity, host-pathogen interactions, marker development, and disease control.

Exploring fine fescues as an option for low‐input golf greens in the north‐central USA

AbstractThere is a need to reduce inputs on golf course putting greens. In the north‐central United States, the use of alternative species, like fine fescues (Festuca spp.), could be part of a solution, but information is needed on management and cultivar choices. Our objectives were twofold: (a) to compare performance of fine fescues (strong creeping red [Festuca rubra L. ssp. rubra Gaudin, STF], slender creeping red [Festuca rubra L. ssp. littoralis (G. Mey.) Auquier, SLF], Chewings [Festuca rubra L. ssp. commutata Gaudin, CHF], and hard fescue [Festuca brevipila Tracey, HDF]) to bentgrasses (creeping bentgrass [Agrostis stolonifera L., CRB], and colonial bentgrass [Agrostis capillaris L., CLB]) managed as low‐input greens treated with 0, 48.9, 97.7, or 195.3 kg N ha−1 yr−1 during 2017–2018; and (b) to evaluate multiple fine fescue cultivars for multiyear performance when maintained as low‐input greens in St. Paul, MN. In 2017, CHF and SLF maintained the highest quality of the fine fescues and maintained higher quality at low N compared with both bentgrasses, primarily due to less dollar spot (Clarireedia spp.). During 2018, fine fescue responses to N were similar to those in 2017, but summer patch (Magnaporthe spp.) disease resulted in decline of some taxa. In the cultivar study, top‐performing cultivars were CHF, most of which performed similarly. However, SLF and STF cultivars performed more variably. Chewings fescue and SLF maintained with 48.9–97.7 kg N ha−1 yr−1 may be alternatives to CRB for low‐input greens in the north‐central United States, primarily due to reduced dollar spot.

A Rapid Molecular Detection System for SdhB and SdhC Point Mutations Conferring Differential Succinate Dehydrogenase Inhibitor Resistance in Clarireedia Populations.

Dollar spot, caused by the ascomycete fungus Clarireedia (formerly Sclerotinia), is one of the most resource-demanding diseases on amenity turfgrasses in North America. Differential resistance to the succinate dehydrogenase inhibitor (SDHI) fungicide class, conferred by singular point mutations on the SdhB, SdhC, and SdhD subunits of the succinate dehydrogenase enzyme (SDH), has been reported in dollar spot as well as many other plant-pathogenic fungal diseases. Four unique mutations were previously reported from Clarireedia field isolates collected from two different cool-season golf courses in Japan and Rhode Island: an amino acid substitution H267Y and a silent mutation (CTT to CTC) at codon 181 on the SdhB subunit gene, and amino acid substitutions G91R and G150R on the SdhC subunit gene. To properly diagnose and monitor SDHI resistance in the field, a rapid detection system for known mutations is crucial. As part of this study, additional SDHI-resistant Clarireedia isolates were collected from Rutgers University research plots and in vitro sensitivity to four SDHI active ingredients was assessed. SdhB, SdhC, and SdhD subunits of these isolates were sequenced to reveal an additional mutation on the SdhB subunit gene, H267R, not previously observed in Clarireedia. Cleaved amplified polymorphic sequence (CAPS) and derived CAPS molecular markers were developed to detect five mutations conferring SDHI resistance in Clarireedia isolates and validated using samples from two additional golf courses in Connecticut and Wisconsin experiencing SDHI field failure. This PCR-based molecular detection system will be useful for continued monitoring, assessment, and delay of SDHI resistance in the field.

Non‐conventional fungicides to control dollar spot disease

AbstractThere are strong societal pressures against the use of synthetic pesticides in our modern urban society. The purpose of this work was to test the efficacy of several substances, many of which are household use items and can be considered non‐conventional, for their ability to control the common turfgrass disease, dollar spot, in lab and field tests. From the over 10 lab tests per treatment and the over 10 field tests between 2015 to 2019, we concluded that among over 20 mostly non‐conventional products applied at different rates and intervals, only ferrous sulfate (21% a.i.) used at 250 g per 100 m2 or ferric sulfate (84.5% a.i.) used at 300 g per 100 m2 applied in 10 L of water per 100 m2 on a weekly basis could provide suppression of dollar spot disease on creeping bentgrass equivalent to a standard fungicide control during periods of low to moderate disease pressure.

The Epichloë festucae Antifungal Protein Efe-AfpA Is also a Possible Effector Protein Required for the Interaction of the Fungus with Its Host Grass Festuca rubra subsp. rubra.

Strong creeping red fescue (Festuca rubra subsp. rubra) is a commercially important low-maintenance turfgrass and is often naturally infected with the fungal endophyte Epichloë festucae. Epichloë spp. are endophytes of several cool-season grass species, often conferring insect resistance to the grass hosts due to the production of toxic alkaloids. In addition to insect resistance, a unique feature of the strong creeping red fescue/E. festucae symbiosis is the endophyte-mediated disease resistance to the fungal pathogen Clarireedia jacksonii, the causal agent of dollar spot disease. Such disease resistance is not a general feature of other grass/ Epichloë interactions. E. festucae isolates infecting red fescue have an antifungal protein gene Efe-afpA, whereas most other Epichloë spp. do not have a similar gene. The uniqueness of this gene suggests it may, therefore, be a component of the unique disease resistance seen in endophyte-infected red fescue. Here, we report the generation of CRISPR-Cas9 Efe-afpA gene knockouts with the goal of determining if absence of the protein in endophyte-infected Festuca rubra leads to disease susceptibility. However, it was not possible to infect plants with the knockout isolates, although infection was possible with the wild type E. festucae and with complemented isolates. This raises the interesting possibility that, in addition to having antifungal activity, the protein is required for the symbiotic interaction. The antifungal protein is a small secreted protein with high expression in planta relative to its expression in culture, all characteristics consistent with effector proteins. If Efe-AfpA is an effector protein it must be specific to certain interactions, since most Epichloë spp. do not have such a gene in their genomes.

Dollar Spot Suppression on Creeping Bentgrass in Response to Repeated Foliar Nitrogen Applications

Dollar spot is caused by the fungus Clarireedia spp. and is the most economically important disease of golf course turfgrass in temperate regions of the United States. Previous research has demonstrated that nitrogen (N) fertilization may reduce dollar spot severity, but the results have been inconsistent, and the impact of N as part of repeated foliar fertilization applications to golf course putting greens remains unclear. Two independent trials were replicated in Madison, Wisconsin and Glenview, Illinois in the 2015, 2016, and 2017 growing seasons. The objective of the first trial was to evaluate the effect of four different N rates applied as urea (4.9, 9.8, 19.4, and 29.3 kg N/ha applied every 2 weeks) on dollar spot severity, and the objective of the second trial was to evaluate the effect of three N sources (calcium nitrate, ammonium sulfate, and ammonium nitrate applied every 2 weeks) on dollar spot severity. Results from the N rate trial at both locations indicated that only the highest (29.3 kg N/ha) rate consistently reduced dollar spot severity relative to the nontreated control. Nitrogen source had minimal and inconsistent impacts on dollar spot severity based on location and year. Although these results show that meaningful reductions in dollar spot severity can be achieved by manipulating N fertilizer application rates, the rate of N needed for disease suppression may be impractical for most superintendents to apply and result in undesirable nontarget impacts.

Identification of a tractable model system and oxalic acid‐dependent symptom development of the dollar spot pathogen Clarireedia jacksonii

AbstractClarireedia jacksonii causes dollar spot disease of cool‐season turfgrasses in the United States and produces the phytotoxin oxalic acid. The role of oxalic acid in host–pathogen interactions of C. jacksonii is unknown and there are multiple challenges to studying these interactions in natural turfgrass hosts. Consequently, identification of model plants to study C. jacksonii–host interactions and the role of oxalic acid in pathogenesis is necessary. Controlled environment inoculation assays were used to evaluate pathogenesis of C. jacksonii in various model plants and investigate the role of oxalic acid in symptom development. Observations at microscopic and macroscopic levels demonstrated that infection progressed similarly in all monocots tested (creeping bentgrass, wheat, barley, rice, Brachypodium distachyon) but not in the dicot Arabidopsis thaliana. Plant oxalic acid content increased from near zero to around 0.2–0.4 mM following inoculation with C. jacksonii in creeping bentgrass, barley, and wheat. Conversely, oxalic acid content remained near zero in A. thaliana and was not well correlated with inoculation in rice and B. distachyon, both of which had higher endogenous oxalic acid levels than other monocots. Time‐course oxalic acid quantification experiments with creeping bentgrass and B. distachyon further supported a link between symptom development and in planta oxalic acid content and identified 48 hr postinoculation as a critical time‐point for investigating the role of oxalic acid in C. jacksonii pathogenesis. These studies demonstrate that various monocots can serve as tractable model systems for studying C. jacksonii–host interactions and that increases in oxalic acid content are associated with C. jacksonii symptom development.

Taxonomical Identification of Clarireedia Species Causing Dollar Spot Disease of Turfgrass in Georgia

Taxonomical Identification of <i>Clarireedia</i> Species Causing Dollar Spot Disease of Turfgrass in Georgia

Real-Time PCR Detection of Clarireedia spp., the Causal Agents of Dollar Spot in Turfgrasses.

Dollar spot is one of the most economically important diseases of turfgrasses. Recent taxonomic revisions have placed the dollar spot fungal pathogens in the new genus Clarireedia, with five species described. The main goal of this study was to develop a quantitative real-time PCR (qPCR) molecular detection assay based on the internal transcribed spacer (ITS) of the ribosomal RNA genes to quantify the abundance of Clarireedia spp. from environmental (field) samples. The qPCR assay was able to detect isolates of the four tested Clarireedia spp. but did not cross react with nontarget fungi, including closely related taxa, other turfgrass pathogens, or other fungal species commonly isolated from turfgrass. The assay is capable of detecting as little as 38.0 fg (3.8 × 10-14 g) of Clarireedia genomic DNA in 3 h. The qPCR assay detected Clarireedia spp. in both symptomatic and asymptomatic creeping bentgrass (Agrostis stolonifera) foliar tissue. Clarireedia spp. were rarely detected in the thatch or soil, indicating that these pathogens are not widely distributed in these areas of the environment. The fact that the pathogen was detected in asymptomatic tissue suggests that creeping bentgrass may be able to tolerate a certain quantity of the pathogens in leaves before disease symptoms appear; however, further research is needed to validate this hypothesis.

Curative Evaluation of Biological Control Agents and Synthetic Fungicides for Clarireedia jacksonii

Clarireedia jacksonii sp. nov. formerly Sclerotinia homoeocarpa F.T. Bennett, one of the causal agents of dollar spot, is the most widespread pathogen in turfgrass systems. Dollar spot (DS) affects both cool- and warm-season grasses, during a wide range of environmental conditions. Field studies were conducted at Clemson University, Clemson, SC, on a creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds) cv. Crenshaw] putting green for 2 consecutive years from August to October in year 1 and July to September in year 2. The objective of the studies was to evaluate biological control agents (BCAs) and synthetic fungicides at reduced rates for their efficacy controlling dollar spot. Four replications of 1.5 × 1.5-m plots were used in the experimental design. Treatments included the following: Bacillus subtilis (BS); plant extract oils (EO) including clove oil + wintergreen oil + thyme oil; extract of Reynoutria sachalinensis (RS); Bacillus licheniformis (BL); chlorothalonil (CL); and azoxystrobin + propiconazole (AzP). Synthetic fungicides were used at reduced rates in combination with biological control agents, to evaluate curative control efficacy of various combinations. All reduced synthetic programs, except CL + EO, provided acceptable disease severity (≤15%) at the end of year 1 and acceptable (≥7) turfgrass visual quality. Azoxystrobin + propiconazole, CL, AzP + BL, AzP + EO, AzP + BS all provided ≤15% disease severity and ≥7 visual turfgrass quality 14 days after the last application in year 2.

Evaluating biological and oil‐based fungicides for dollar spot suppression on turfgrass

AbstractDollar spot (caused by Clarireedia jacksonii) receives more fungicide applications than any other turfgrass disease. Increasing restrictions on fungicide usage and expanding reports of fungicide resistant fungal populations have resulted in renewed interest in biological and plant‐based control of turfgrass diseases. Six commercially available biological fungicides (Actinovate AG, Double Nickel LC, Nortica, Rhapsody, Serende Opti, Zio) and two oil‐based fungicides (Civitas, Timorex Gold) were evaluated for dollar spot control on a creeping bentgrass putting green in Madison, WI, USA in 2017 and 2018. No biological or oil‐based fungicide provided effective full‐season dollar spot control compared to the synthetic fungicide boscalid. However, Civitas mineral oil provided levels of dollar spot control similar to boscalid on 9 of 12 rating dates over both years. The remaining treatments tested provided levels of dollar spot control and turf quality similar to boscalid ranging from 4 to 7 of a possible 12 rating dates. These results indicate that the biological fungicides tested here failed to provide commercially acceptable dollar spot control under moderate disease pressure in the midwestern U.S. The mineral oil Civitas did provide effective suppression under moderate disease pressure, while the tea tree oil Timorex Golf did not. Certain oil‐based fungicides like Civitas can provide effective dollar spot control during periods of low to moderate disease pressure, but more research is needed before biological fungicides can be successfully integrated into a dollar spot management program.

Oxalic Acid Production in Clarireedia jacksonii Is Dictated by pH, Host Tissue, and Xylan.

Dollar spot is caused by the fungus Clarireedia jacksonii and is the most common disease of golf course turfgrass in temperate climates. Oxalic acid (OA) is an important pathogenicity factor in other fungal plant pathogens, such as the dicot pathogen Sclerotinia sclerotiorum, but its role in C. jacksonii pathogenicity on monocot hosts remains unclear. Herein, we assess fungal growth, OA concentration, and pH change in potato dextrose broth (PDB) following incubation of C. jacksonii. In addition, OA production by C. jacksonii and S. sclerotiorum was compared in PDB amended with creeping bentgrass or common plant cell wall components (cellulose, lignin, pectin, or xylan). Our results show that OA production is highly dependent on the environmental pH, with twice as much OA produced at pH 7 than pH 4 and a corresponding decrease in PDB pH from 7 to 5 following 96 h of C. jacksonii incubation. In contrast, no OA was produced or changes in pH observed when C. jacksonii was incubated in PDB at a pH of 4. Interestingly, C. jacksonii increased OA production in response to PDB amended with creeping bentgrass tissue and the cell wall component xylan, a major component of grass cell walls. S. sclerotiorum produced large amounts of OA relative to C. jacksonii regardless of treatment, and no treatment increased OA production by this fungus, though pectin suppressed S. sclerotiorum’s OA production. These results suggest that OA production by C. jacksonii is reliant on host specific components within the infection court, as well as the ambient pH of the foliar environment during its pathogenic development.

Baseline sensitivity and control efficacy of fluazinam against Clarireedia homoeocarpa

Clarireedia homoeocarpa (formerly called Sclerotinia homoeocarpa) causes dollar spot, one of the most important diseases of turfgrasses worldwide. The dinitroaniline fungicide fluazinam was recently registered for turfgrass. In this study, baseline sensitivity, toxicity and control efficacy of fluazinam against C. homoeocarpa were investigated. The frequency of sensitivities had a unimodal distribution (Kolmogorov-Smirnov, P = 0.20). The mean EC50 value was 0.0226 ± 0.0109 μg ml−1 with individual values ranging from 0.0032 to 0.0440. Fluazinam increased the number of hyphal offshoots, cell membrane permeability, and inhibited oxalic acid production. No positive cross-resistance between fluazinam and thiophanate-methyl, propiconazole, or boscalid was observed. Fluazinam at 1 μg ml−1 can reach 90.10% preventative control efficacy on detached leaves; while, the curative control efficacy of fluazinam at 5 μg ml−1 was less than 60%. The preventative control efficacy of fluazinam in the field was consistently more than 97% in 2017 and 2018. The curative control efficacy in the field reached 75.56% in 2017 and 95.91% in 2018. Both preventative and curative control efficacies of fluazinam were better than propiconazole and fludioxinil over two years. The results have important implications for managing dollar spot disease and fungicide resistance problems in C. homoeocarpa.

The Hsp90 Inhibitor, Monorden, Is a Promising Lead Compound for the Development of Novel Fungicides.

Endophytic fungi are great resources for the identification of useful natural products such as antimicrobial agents. In this study, we performed the antifungal screening of various plant endophytic fungi against the dollar spot pathogen Sclerotinia homoeocarpa and finally selected Humicola sp. JS-0112 as a potential biocontrol agent. The bioactive compound produced by the strain JS-0112 was identified as monorden known as an inhibitor of heat shock protein 90 (Hsp90). Monorden exhibited strong antagonistic activity against most tested plant pathogenic fungi particularly against tree pathogens and oomycetes with the minimum inhibitory concentration values less than 2.5 μg mL–1. Extensive in planta assays revealed that monorden effectively suppressed the development of several important plant diseases such as rice blast, rice sheath blight, wheat leaf rust, creeping bentgrass dollar spot, and cucumber damping-off. Especially, it showed much stronger disease control efficacy against cucumber damping-off than a synthetic fungicide chlorothalonil. Subsequent molecular genetic analysis of fission yeast and Fusarium graminearum suggested that Hsp90 is a major inhibitory target of monorden, and sequence variation among fungal Hsp90 is a determinant for the dissimilar monorden sensitivity of fungi. This is the first report dealing with the disease control efficacy and antifungal mechanism of monorden against fungal plant diseases and we believe that monorden can be used as a lead molecule for developing novel fungicides with new action mechanism for the control of plant diseases caused by fungi and oomycetes.

Elucidation of Terpenoid Biosynthesis in Sclerotinia

Terpenes are a large class of specialized metabolites found in plant and fungus species that have been widely studied for their medicinal and cytotoxic properties. The plant pathogenic fungus Sclerotinia homoeocarpa was previously shown to produce eleven nortetralabdane compounds that exhibit strong antiplasmodial and growth inhibitive properties. Our objective is to elucidate the biosynthesis of these unique terpene compounds in S. homoeocarpa. Genome mining identified two terpene cyclases as well as multiple clustered cytochromes P450 (CYPs). Combinatorial expression in Escherichia coli and GC‐MS analysis of extracts revealed that one cyclase, ShTPS1, is a bifunctional diterpene synthase that produces the 20‐carbon compound pimara‐8(14),15‐diene. This diterpene likely acts as a scaffold to be modified by downstream CYPs into nortetralabdanes. The second cyclase, ShTPS2, produces several 25‐carbon sesterterpenes, one of the least well‐characterized subsets of terpenes and a frontier for pharmaceutical research. The discovery of ShTPS2 is uniquely interesting due to its promiscuity and the rarity of characterized bifunctional sesterterpene synthases ‐ terpene synthases with a chimeric prenyltransferase domain. Homology modeling of ShTPS2 identified targets for site‐directed mutagenesis in the prenyltransferase and terpene cyclase domains. Mutations in these areas reveal both the functional plasticity of the enzyme and that the promiscuity may result from cationic intermediates of a single terpene cyclase pathway. This research contributes to understanding the diversity of terpene biosynthesis in fungi and allows for the biosynthesis of compounds of interest that are naturally produced at low levels, enabling future work to investigate their function.Support or Funding InformationThis work was supported by the Massachusetts Agricultural Experiment Station as well as the University of Massachusetts Amherst Commonwealth Honors College and Department of Biochemistry and Molecular Biology.

Effects of rolling and N-fertilization on dollar spot and Microdochium patch on golf greens in Scandinavia

Dollar spot was officially documented in Scandinavia in 2013 and the spread and damage from this disease has increased during last years. In summer 2017, on the golf greens with red fescue (Vallda GC, Sweden) and with the mixture of red fescue, colonial bentgrass and annual bluegrass (Roskilde GC, Denmark) rolling 2 times per week reduced dollar spot 61% and 37% and rolling 4 times per week reduced dollar spot 95% and 54%, respectively. Thus, rolling 3-4 times per week can be recommended on golf greens with dollar spot pressure. In the experiment 2018 dollar spot was reduced 24% with increase in nitrogen from 150 to 240 kg ha-1 yr-1 on creeping bentgrass/annual bluegrass golf green (Kävlinge GK, Sweden). However, the increased N-rate lead to a higher degree Microdochium patch from 14% to 30%.