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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., Competing Interests: The author(s) declare no conflict of interest.

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., Competing Interests: The author(s) declare no conflict of interest.

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.

The genus Clarireedia contains multiple species causing dollar spot (DS) on turfgrass worldwide. In November 2020, 119 Clarireedia isolates were obtained from symptomatic seashore paspalum at golf courses in Hainan province and identified to species level based on partial sequence of the internal transcribed spacer (ITS) region. A total of 45 and 22 isolates were identified as C. paspali and C. monteithiana , respectively; the remaining 52 isolates defined a new clade. Isolates from this clade were further selected for phylogenetic, morphological, and biological analyses. Maximum likelihood and Bayesian methods were implemented to obtain phylogenetic trees for partial sequences of the ITS, EF-1α , and McM7 genes. The selected isolates consistently fell into a distinct, well-supported clade within Clarireedia . Morphological and biological characteristics were observed among the different species in Clarireedia . Altogether, this study described a new species, Clarireedia hainanense , which has widespread distribution in Hainan, China. These findings may have important implications for the management of DS disease.

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 Sdh B, Sdh C, 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 Sdh B subunit gene, and amino acid substitutions G91R and G150R on the Sdh C 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. Sdh B, Sdh C, and SdhD subunits of these isolates were sequenced to reveal an additional mutation on the Sdh B 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.