Dollar Spot Research Articles

Horizontal and Vertical Distribution of Clarireedia spp. in Asymptomatic and Symptomatic Creeping Bentgrass Cultivars.

Dollar spot is an important disease of both cool- and warm-season turfgrasses caused by six fungal species in the genus Clarireedia, yet the ecology and epidemiology of these pathogens remains poorly understood. The goal of this study was to determine the distribution of Clarireedia in asymptomatic and symptomatic creeping bentgrass (Agrostis stolonifera) in the field using a previously developed quantitative PCR assay. To determine the horizontal distribution of the pathogen, the abundance of Clarireedia spp. was measured in leaf and crown tissue from 90, 1-cm-diameter cores spaced 10 cm apart in May 2019 and 2020 (asymptomatic tissue) and August 2019 and July 2020 (symptomatic tissue). Thirty-seven to 69% of cores sampled from asymptomatic turfgrass and 77 to 95% of cores taken from symptomatic turfgrass yielded positive detections for Clarireedia. Spatial analysis indicated that Clarireedia was randomly distributed in the field in both asymptomatic and symptomatic turfgrass. To assess the vertical distribution of the pathogen, the abundance of Clarireedia was measured in the foliar, crown, and thatch layers of 39, 1-cm-diameter × 2.5-cm-deep cores of creeping bentgrass maintained at fairway height (9.5 mm) during 2019 and 2020. Clarireedia was most abundant in foliar tissue, followed by crown tissue and thatch (lowest abundance) throughout the 2-year study. Both studies provide evidence that Clarireedia is widely distributed in turfgrass swards prior to symptom development and can persist within turfgrass as an endophyte. These findings will improve our understanding of Clarireedia epidemiology and may lead to more sustainable dollar spot management.

Optimizing liquid‐applied iron sulfate rate and application interval for dollar spot suppression on golf course fairways

AbstractIron sulfate applications reduce dollar spot severity on golf course turfgrass, but further optimizing the use of iron sulfate may increase efficacy and encourage more widespread adoption by golf course superintendents. Three iron sulfate rates (9, 18, 36 kg ha−1), two application intervals (7 and 14 days), three water volumes (306, 612, and 1223 L ha−1), and combinations with fertilizer and fungicide products were evaluated at field locations in Madison, WI, Bloomington, MN, and Blacksburg, VA, in 2018 and 2019. Iron sulfate rate decreased dollar spot at all locations in a dose‐dependent manner, and 7‐day applications were more efficacious than 14‐day applications. Water volume had no impact on disease severity at any location and combining iron sulfate with fertilizer had minimal impact as well. These results demonstrate improved iron sulfate strategies for dollar spot management and can be implemented by golf course superintendents in areas where fungicide resistance and fungicide regulations limit the use of traditional fungicides.

Field Evaluation of Fluazinam Fungicide in Dollar Spot Populations Confirmed In Vitro Insensitivity.

Fluazinam, a fungicide widely used in agriculture and turf management, was traditionally thought to pose a low risk of resistance. However, our in vitro sensitivity test conducted in 2021 revealed reduced sensitivity to fluazinam in dollar spot, highlighting the need for more vigilant field monitoring. In 2022 and 2023, we evaluated the field responses of four Clarireedia jacksonii isolates with varying in vitro sensitivity to fluazinam. Fluazinam was used at both a full labeled rate (0.5 oz/1,000 ft2) and a half-rate (0.25 oz/1,000 ft2) to evaluate the effectiveness in isolate-inoculated plots in the field. In 2022, both natural and sensitive isolates showed significantly better control compared to insensitive isolates under both half- and full-rate treatments. However, in 2023, half-rate fluazinam demonstrated limited control under high disease pressure, providing relative disease control of dollar spot less than 45% across all treatments. In contrast, full-rate fluazinam maintained significantly better control of natural and sensitive isolates compared with insensitive isolates. Our results, showing that in vitro insensitivity leads to field insensitivity under inoculated conditions, suggest the development of fluazinam insensitivity in the C. jacksonii population. This highlights the need for judicious use of fluazinam and the establishment of continuous resistance monitoring. Furthermore, the loss of control observed when fluazinam was applied at half-rates under high disease pressure highlights the importance of careful fungicide use.

Probe-Based Loop-Mediated Isothermal Amplification Assay for Rapid Detection of Two Clarireedia spp., the Causal Agent of Dollar Spot of Turfgrass.

Dollar spot is a major fungal disease affecting turfgrass worldwide and can quickly destroy turfgrass swards. An assimilating probe-based loop-mediated isothermal amplification (LAMP) assay was developed to detect Clarireedia monteithiana and C. jacksonii, the causal agents of dollar spot within the continental United States. Five LAMP primers were designed to target the calmodulin gene with the addition of a 6-carboxyl-fluorescein florescent assimilating probe, and the temperature amplification was optimized for C. jacksonii and C. monteithiana identification. The minimum amount of purified DNA needed for detection was 0.05 ng μl-1. Specificity assays against host DNA and other turfgrass pathogens were negative. Successful LAMP amplification was also observed for dollar spot-infected turfgrass field samples. Further, a DNA extraction technique via rapid heat-chill cycles and visualization of LAMP results via a florescent flashlight was developed and adapted for fast, simple, and reliable detection in 1.25 h. This assimilating probe-based LAMP assay has proved successful as a rapid, sensitive, and specific method for the detection of C. monteithiana and C. jacksonii in pure cultures and from symptomatic turfgrass leaves blades. The assay represents a promising technology to be used in the field for on-site, point-of-care pathogen detection.

Determining the optimal ratio of resistant to susceptible bentgrass cultivars to reduce dollar spot severity

AbstractDollar spot, caused by Clarireedia spp., is the most prevalent disease on creeping bentgrass golf fairways. Interseeding newer dollar spot‐resistant cultivars into susceptible bentgrass stands could reduce dollar spot severity and the need for resultant fungicide use. This study was conducted to determine the optimal ratio of resistant to susceptible cultivars in a blend that will result in dollar spot reduction. Greenhouse experiments were conducted on cultivar blend ratios (0%, 10%, 25%, 50%, 75%, 90%, 100%) of dollar spot‐resistant (Pure Select, 007XL, Coho) and susceptible (Penncross) bentgrass challenged with inoculation of two Clarireedia spp. isolates. Disease severity was determined using visual estimates and digital image analysis. Dollar spot severity was significantly influenced by the Clarireedia isolate, with a fungicide‐resistant isolate being more aggressive and producing more disease than a sensitive one. Dollar spot severity was highest on Penncross alone, with no statistical differences observed among the resistant cultivar monostands. Mean disease severity of the blended cultivar ratios was divided into three statistically different groups—low resistance (10% and 25%), medium resistance (50% and 75%), and high resistance (90% and 100%). Compared to Penncross, blending a 10% resistant cultivar reduced AUDPC (area under the disease progress curve) values by 2% and 3% in Experiments 1 and 2, respectively, while blending a 90% resistant cultivar yielded 20% and 32% reductions. These results indicate dollar spot severity decreases as the ratio of the resistant cultivar in a stand increases, and blending resistant cultivars into susceptible has the potential for reducing disease.

Leveraging deep learning for dollar spot detection and quantification in turfgrass

Leveraging deep learning for dollar spot detection and quantification in turfgrass

The role of oxalic acid in Clarireedia jacksonii virulence and development on creeping bentgrass.

Dollar spot is a destructive foliar disease of amenity turfgrass caused by the fungus Clarireedia spp., and mainly Clarireedia jacksonii on the northern US region's cool-season grass. Oxalic acid (OA) is an important pathogenicity factor in related fungal plant pathogens such as Sclerotinia sclerotiorum, however, the role of OA in the pathogenic development of C. jacksonii remains unclear due to its recalcitrance to genetic manipulation. To overcome these challenges, a CRISPR/Cas9-mediated homologous recombination approach was developed. Using this novel approach, the oxaloacetate acetylhydrolase (Oah) gene that is required for the biosynthesis of OA was deleted from C. jacksonii wild-type stain. Two independent knockout mutants, ΔCjoah-1 and ΔCjoah-2, were generated and inoculated on potted creeping bentgrass along with a wild-type isolate (WT) and a genome sequenced isolate LWC-10. After 12 days, bentgrass inoculated with the mutants ΔCjoah-1 and ΔCjoah-2 exhibited 59.41% lower dollar spot severity compared to the WT and LWC-10 isolates. Oxalic acid production and environmental acidification were significantly reduced in both mutants when compared to the WT and LWC-10. Surprisingly, stromal formation was also severely undermined in the mutants in vitro, suggesting a critical developmental role of OA independent of plant infection. These results demonstrate that OA plays a significant role in C. jacksonii virulence and provide novel directions for future management of dollar spot.

Effect of turfgrass care products on soil biological health, disease suppression, and turfgrass quality

Despite the wide use of turfgrass care products such as wetting agents (WAs), plant growth regulators (PGRs), and biological products (BPs), little is known about their effect on soil biological health, turfgrass quality, and disease suppression. Studies were conducted to evaluate the effect of some commonly used turfgrass care products on soil biological health, dollar spot suppression, and turfgrass quality. The turfgrass care products were: nine WAs (Vivax, Fleet, Magnus, Cascade, Dispatch, Duplex, Pervade, Sixteen90, and Revolution); four PGRs (Anuew, Trimmit, Proxy, and Cutless) and; three BPs (Plant Helper, KaPreRemeD8-NSL, and KaPreRemeD8-NSP). Potted bentgrass (Agrotis stolonifera L.) were treated independently with the WAs, PGRs, and BPs, and deionized water was used as a control. Soil samples were collected from the pots at 7 and 14 weeks after treatment (WAT) and analyzed for soil biological health using soil respiration, urease, and phosphatase activities as indicators. Disease suppression was evaluated by inoculating potted bentgrass with an isolate of Clarireedia jacksonii, the causal agent of dollar spot of cool season grasses and the infection was visually assessed at intervals of 10 days. The WAs Dispatch, Fleet, Magnus, and Vivax stimulated rate of soil respiration at 7 WAT compared to the control. The PGRs Cutless, Trimmit, and Proxy had no effect on soil respiration whereas Anuew suppressed soil respiration. Turfgrass quality was improved by the WAs Revolution, Cascade, Pervade, Duplex, and Sixteen90 at 7 WAT, but none of the PGRs and BPs improved turf quality. Cascade stimulated phosphatase activity and was the only product to impact this indicator. None of the products had a significant effect on dollar spot suppression. These results could guide turfgrass growers and professionals in making decisions that enhance the quality of turfgrass without compromising the health of the soil that sustains it.

Abstract 2442 Finding the mRNA sequence of Methylcitrate synthase in Sclerotinia Homoeocarpa using Bioinformatics

Abstract 2442 Finding the mRNA sequence of Methylcitrate synthase in Sclerotinia Homoeocarpa using Bioinformatics

Genome-wide transcriptional analyses of Clarireedia jacksonii isolates associated with multi-drug resistance.

Emerging multidrug resistance (MDR) in Clarireedia spp. is a huge challenge to the management of dollar spot (DS) disease on turfgrass. Insight into the molecular basis of resistance mechanisms may help identify key molecular targets for developing novel effective chemicals. Previously, a MDR isolate (LT586) of C. jacksonii with significantly reduced sensitivities to propiconazole, boscalid, and iprodione, and a fungicide-sensitive isolate (LT15) of the same species were isolated from creeping bentgrass (Agrostis stolonifera L.). The present study aimed to further explore the molecular mechanisms of resistance by using genome-wide transcriptional analyses of the two isolates. A total of 619 and 475 differentially expressed genes (DEGs) were significantly down and upregulated in the MDR isolate LT586, compared with the sensitive isolate LT15 without fungicide treatment. Three hundreds and six and 153 DEGs showed significantly lower and higher expression in the MDR isolate LT586 than those in the sensitive isolate LT15, which were commonly induced by the three fungicides. Most of the 153 upregulated DEGs were xenobiotic detoxification-related genes and genes with transcriptional functions. Fifty and 17 upregulated DEGs were also commonly observed in HRI11 (a MDR isolate of the C. jacksonii) compared with the HRS10 (a fungicide-sensitive isolate of same species) from a previous study without and with the treatment of propiconazole, respectively. The reliability of RNA-seq data was further verified by qRT-PCR method using a few select potentially MDR-related genes. Results of this study indicated that there were multiple uncharacterized genes, possibly responsible for MDR phenotypes in Clarireedia spp., which may have important implications in understanding the molecular mechanisms underlying MDR resistance.

Topdressing Biochar Compost Mixtures and Biological Control Organism Applications Suppress Foliar Pathogens in Creeping Bentgrass Fairway Turf.

Biochar, compost, and biological control agents can suppress pathogens on their own; however, their reliability and efficacy are not as acceptable as synthetic fungicides commonly used to suppress pathogens. A multiyear field study was initiated to evaluate combinations of monthly applications of a biochar compost mixture and weekly or biweekly Bacillus subtilis QST713 applications for their ability to suppress foliar pathogens on a creeping bentgrass (Agrostis stolonifera L.) fairway and to measure their impact on strain QST713 establishment. Disease severity and turfgrass quality were measured every 14 days throughout the growing season. Populations of strain QST713 were quantified by quantitative PCR analysis on DNA extracted from foliage samples collected throughout the trial. Biochar compost mixture applications increased turfgrass quality in both years of the study and reduced dollar spot (Clarireedia jacksonii Salgado-Salazar) severity in 2021. Weekly strain QST713 applications reduced copper spot (Gloeocercospora sorghi D. C. Bain & Edgerton) severity compared with biweekly applications and the nontreated control in 2020, yet monthly biochar compost mixture with weekly strain QST713 applications completely suppressed copper spot in 2021. Populations of strain QST713 were highest in weekly treated plots, and monthly biochar compost mixture applications did not affect strain QST713 establishment. Although there was not an interaction between biochar compost mixture and strain QST713 applications, implementing both in a season-long program will benefit turfgrass health and reduce disease severity.

Activity of the Succinate Dehydrogenase Inhibitor Fungicide Benzovindiflupyr Against Clarireedia spp.

Dollar spot (DS), caused by Clarireedia spp. (formerly Sclerotinia homoeocarpa), is one of the most important diseases of turfgrasses worldwide. Benzovindiflupyr, a pyrazole carboxamide fungicide belonging to succinate dehydrogenase inhibitors, was recently registered for DS control. In this study, baseline sensitivity, toxicity, and control efficacy of benzovindiflupyr against Clarireedia spp. were evaluated. The frequency of sensitivities had a unimodal distribution (Kolmogorov-Smirnov, P > 0.10). The mean EC50 value was 1.109 ± 0.555 μg/ml, with individual values ranging from 0.160 to 2.548 μg/ml. Benzovindiflupyr increased the number of hyphal offshoots and cell membrane permeability and inhibited oxalic acid production. Positive cross-resistance was observed between benzovindiflupyr and boscalid, but not between benzovindiflupyr and thiophanate-methyl, propiconazole, or iprodione. Benzovindiflupyr showed high protective and curative control efficacies in vivo and in field applications. Both protective and curative control efficacies of benzovindiflupyr were significantly better than propiconazole, and equivalent to boscalid, over 2 years of field research. The results have important implications for managing DS and fungicide resistance problems in Clarireedia spp.

Spo0A-dependent antifungal activity of a plant growth promoting rhizobacteria Bacillus subtilis strain UD1022 against the dollar spot pathogen (Clarireedia jacksonii)

Dollar spot is an economically important foliar disease of turfgrass caused by Clarireedia spp. Increased use of chemical fungicides for disease management has possible negative effects on the environment and human health. The quest for eco-friendly alternatives to fungicides is driving the development of new biological strategies for managing dollar spot. In the present study, an analysis of antifungal activity of the plant growth promoting rhizobacteria (PGPR) Bacillus subtilis strain UD1022 (hereafter UD1022) and plant health products (PHPs) (Acibenzolar-S-methyl, kelp extract, fosetyl-Al, and trinexapac-ethyl) against Clarireedia jacksonii for control of the turfgrass fungal disease dollar spot was conducted. In vitro assays revealed that UD1022 has significant inhibitory effects against the mycelial growth of C. jacksonii. Of all the treatments, wild type UD1022 and a non-ribosomal peptide mutant (sfp¯) showed potential antagonism against C. jacksonii with inhibition rate of 17.2 % and 18.4%, respectively. Interestingly a Bacillus-derived broad antifungal compound (surfactin) and PHPs showed no direct antagonistic activity against dollar spot pathogen and were statistically like the untreated control. All the mutants of UD1022 except spo0A¯ showed varying but significant inhibition of the fungal pathogen suggesting that spo0A gene may be directly involved in the antagonism against C. jacksonii. Bacterial volatile compounds (BVCs) of UD1022 may not be involved in antagonism as no fungal inhibition was observed in the indirect assay using split petri plates. Filter sterilized cell free lysate (CFL) as well as heat treated CFL of UD1022 bacterial culture did not show any fungal inhibition indicating a primary role of live bacterial cells and not bacterial-derived or secreted compounds in fungal growth inhibition. The results indicate UD1022 to possess the potential to be extended for the biocontrol of dollar spot of turfgrass.

Sensitivity of Clarireedia spp. to benzimidazoles and dimethyl inhibitors fungicides and efficacy of biofungicides on dollar spot of warm season turfgrass.

Dollar spot caused by Clarireedia spp. (formerly Sclerotinia homoeocarpa) is an economically destructive fungal disease of turfgrass that can significantly compromise turf quality, playability, and aesthetic value. Fungicides are frequently used to manage the disease but are costly and potentially unfavorable to the environment. Repeated use of some active ingredients has resulted in reduced efficacy on C. jacksonii causing dollar spot in cool-season turfgrasses in the US. Experiments were conducted to study fungicide sensitivity of Clarireedia spp. as well as to develop alternatives to fungicides against dollar spot on warm-season turfgrass in Georgia. First, 79 isolates of Clarireedia spp. collected across the state were tested on fungicide-amended agar plates for their sensitivity to thiophanate-methyl (benzimidazole) and propiconazole (dimethyl inhibitor). Seventy-seven isolates (97.5%) were sensitive (0.001 to 0.654 μg/mL) and two isolates (2.5%) were found resistant (>1000 μg/mL) to thiophanate-methyl. However, in the case of propiconazole, 27 isolates (34.2%) were sensitive (0.005 to 0.098 μg/mL) while 52 isolates (65.8%) were resistant (0.101 to 3.820 μg/mL). Next, the efficacy of three bio- and six synthetic fungicides and ten different combinations were tested in vitro against C. monteithiana. Seven bio- and synthetic fungicide spray programs comprising Bacillus subtilis QST713 and propiconazole were further tested, either alone or in a tank mix in a reduced rate, on dollar spot infected bermudagrass 'TifTuf' in growth chamber and field environments. These fungicides were selected as they were found to significantly reduce pathogen growth up to 100% on in vitro assays. The most effective spray program in growth chamber assays was 100% B. subtilis QST713 in rotation with 75% B. subtilis QST713 + 25% propiconazole tank mix applied every 14 days. However, the stand-alone application of the biofungicide B. subtilis QST713 every seven days was an effective alternative and equally efficacious as propiconazole, suppressing dollar spot severity and AUDPC up to 75%, while resulting in acceptable turf quality (>7.0) in field experiments. Our study suggests that increased resistance of Clarireedia spp. to benzimidazoles and dimethyl inhibitors warrants continuous surveillance and that biofungicides hold promise to complement synthetic fungicides in an efficacious and environmentally friendly disease management program.

Comparative physiological and transcriptome analysis provide insights into the inhibitory effect of 6-pentyl-2H-pyran-2-one on Clarireedia jacksonii

Clarireedia spp. is a destructive phytopathogenic fungus that causes turf dollar spot of bent-grass, leading to widespread lawn death. In this study, we explored the antifungal capability of 6-pentyl-2H-pyran-2-one (6PP), a natural metabolite volatilized by microorganisms, which plays an important role in the biological control of turfgrass dollar spot. However, the mechanisms by which 6PP inhibits Clarireedia jacksonii remain unknown. In the present study, C. jacksonii mycelial growth was inhibited by the 6PP treatment and the 6PP treatment damaged cell membrane integrity, causing an increase in relative conduc-tivity. Furthermore, physiological and biochemistry assay showed that 6PP treatment can enhance reactive oxygen species (ROS) levels, malondialdehyde (MDA) content obviously increased with 6PP exposure, increased alchohol dehydrogenase (ADH) and depleted acetalde-hyde dehydrogenase (ALDH), and activated the activities of many antioxidant enzymes in C. jacksonii. Gen Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that some genes in C. jacksonii after 6PP treatment related to integrity of the cell wall and membrane, and oxidative stress were significantly downregulated. It is worth mentioning that the fatty acid degradation pathway is significantly upregulated, with an increase in ATP content and ATP synthase activity, which may promote fungal cell apoptosis. Moreover, we found that the expression of ABC transporters, and glutathione metabolism encoding genes were increased to respond to external stimuli. Taken together, these findings revealed the potential antifungal mechanism of 6PP against Clarireedia spp., which also provides a theoretical basis for the commercial utilization of 6PP as a green pesticide in the future.

Genetic diversity of colonial bentgrass Agrostis capillaris based on simple sequence repeat markers and high‐resolution melt analysis with haplotype scoring

AbstractColonial bentgrass (Agrostis capillaris) is a tetraploid rhizomatous bentgrass that generally exhibits improved resistance to the important fungal disease dollar spot and has more tolerance to water‐deficit stress than the more widely grown creeping bentgrass (Agrostis stolonifera). Interspecific hybridization between these two species is possible and efforts to understand the genetic mechanisms of enhanced biotic and abiotic stress resistance in colonial bentgrass are proceeding. To gain a better understanding of the level of genetic diversity in cultivated colonial bentgrasses and to determine if genotypes with improved interspecific hybridization potential can be identified, nine colonial bentgrass cultivars and one creeping bentgrass cultivar were screened with 48 colonial bentgrass‐derived simple sequence repeat markers. Twenty‐one primer pairs were found to produce reliable amplification, and these markers were scored using high‐resolution melt analysis to generate haplotypes that were used to evaluate cultivar relationships. The nine colonial bentgrass cultivars could be placed into two groups and overall showed limited levels of diversity. The creeping bentgrass cultivar was distinct and individual genotypes within each species exhibited haplotypes more common in the alternate species, suggesting that these markers may be useful for selecting genotypes with enhanced interspecific hybridization potential.

Comparing methods to quantify cover in turfgrass research

AbstractTurfgrass cover can be assessed qualitatively using visual ratings, but quantitative turfgrass cover measurements are desired for producing unbiased data. Digital image analysis and point intercept are two quantitative percent cover data collection methods used in turfgrass research. A potential weakness of digital image analysis is the difficulty in evaluating color variation. Considering this, a series of controlled environment and field experiments were conducted to evaluate the accuracy of the point intercept method compared to using a digital grid, digital image analysis, and visual ratings when utilized in turfgrass research. To explore this topic, four experiments were conducted in Corvallis, OR, and one in New Brunswick, NJ. Results from research conducted in Corvallis, OR, determined that the closest point intercept spacing (2.5 cm) resulted in a percent cover that was not statistically different from the known cover and the lowest variance, but the greatest amount of time required to collect the data. Digital image analysis was the most consistent method for measuring percent cover when a known percent cover was being quantified. The estimate of the percent dollar spot cover was reduced by a single pigment application regardless of the data collection method. In the absence of pigment applications, the point intercept frame, digital image analysis, and visual ratings were well‐correlated methods used to assess dollar spot cover. Digital image analysis was not correlated with the other data collection methods when used to evaluate percent anthracnose cover. The research conducted in New Brunswick, NJ, determined that the point intercept method and digital image analysis are well‐correlated methods for quantifying turfgrass establishment from seed.

The Epichloë festucae Antifungal Protein Efe-AfpA Has Activity against Numerous Plant Pathogens.

Fungal plant pathogens can present major problems for most crop species. Currently, control of fungal diseases relies heavily on the use of fungicides. However, there are problems associated with fungicide use, including potential toxicity to non-target organisms and the development of resistance in the target fungus. New strategies are being sought to reduce fungicide use. One area of active research is the potential use of antifungal proteins from various fungal species as alternatives or complements to traditional fungicides. An antifungal protein, Efe-AfpA, from the fungal endophyte Epichloë festucae was previously found to protect plants from the pathogen Clarireedia jacksonii, the causal agent of dollar spot disease. Here we report that Efe-AfpA also has inhibitory activity against other important plant pathogens. These results suggest that it may be possible to develop Efe-AfpA as a biofungicide to target a broad range of destructive plant pathogens.

Genome Resources for Four Clarireedia Species Causing Dollar Spot on Diverse Turfgrasses.

Dollar spot (DS) is a destructive fungal disease impacting almost all warm- and cool-season turfgrasses worldwide. Multiple fungal species in the genus Clarireedia are causal agents of DS. Here, we present whole-genome assemblies of nine fungal isolates in the genus Clarireedia, including four species (C. paspali, C. hainanense, C. jacksonii, and C. monteithiana) causing DS on seashore paspalum (Paspalum vaginatum Sw.), creeping bentgrass (Agrostis stolonifera L.), and Kentucky bluegrass (Poa pratensis L.) in China. This work provides valuable baseline genomic data to support further research and management of DS pathogens on turfgrasses.

Whole genome sequencing of Clarireedia aff. paspali reveals potential pathogenesis factors in Clarireedia species, causal agents of dollar spot in turfgrass.

Dollar spot is one of the most damaging diseases in turfgrass, reducing its quality and playability. Two species, Clarireedia monteithiana and C. jacksonii (formerly Sclerotinia homoeocarpa) have been reported so far in the United States To study the Clarireedia genome, two isolates H2 and H3, sampled from seashore paspalum in Hawaii in 2019 were sequenced via Illumina paired-end sequencing by synthesis technology and PacBio SMRT sequencing. Both isolates were identified as C. aff. paspali, a novel species in the United States Using short and long reads, C. aff. paspali H3 contained 193 contigs with 48.6Mbp and presented the most completed assembly and annotation among Clarireedia species. Out of the 13,428 protein models from AUGUSTUS, 349 cytoplasmic effectors and 13 apoplastic effectors were identified by EffectorP. To further decipher Clarireedia pathogenicity, C. aff. paspali genomes (H2 and H3), as well as available C. jacksonii (LWC-10 and HRI11), C. monteithiana (DRR09 and RB-19) genomes were screened for fifty-four pathogenesis determinants, previously identified in S. sclerotiorum. Seventeen orthologs of pathogenicity genes have been identified in Clarireedia species involved in oxalic acid production (pac1, nox1), mitogen-activated protein kinase cascade (pka1, smk3, ste12), appressorium formation (caf1, pks13, ams2, rgb1, rhs1) and glycolytic pathway (gpd). Within these genes, 366 species-specific SNPs were recorded between Clarireedia species; twenty-eight were non-synonymous and non-conservative. The predicted protein structure of six of these genes showed superimposition of the models among Clarireedia spp. The genomic variations revealed here could potentially lead to differences in pathogenesis and other physiological functions among Clarireedia species.