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Title: Clarireedia: A new fungal genus comprising four pathogenic species responsible for dollar spot disease of turfgrass

item BEIRN, LISA - Rutgers University
item Ismaiel, Ed - Ed
item BOEHM, MICHAEL - The Ohio State University
item CARBONE, IGNAZIO - North Carolina State University
item PUTNAM, ALEXANDER - North Carolina State University
item TREDWAY, LANE - Syngenta Crop Protection
item CLARKE, BRUCE - Rutgers University
item Crouch, Jo Anne

Submitted to: Fungal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2018
Publication Date: 4/23/2018
Citation: Salgado-Salazar, C., Beirn, L.A., Ismaiel, A.A., Boehm, M.J., Carbone, I., Putnam, A.I., Tredway, L.P., Clarke, B.B., Crouch, J.A. 2018. Clarireedia: A new fungal genus comprising four pathogenic species responsible for dollar spot disease of turfgrass. Fungal Biology. 122(8):761-773.

Interpretive Summary: Turfgrass covers millions of acres of parks, lawns, recreational fields and golf courses around the world. Outbreaks of dollar spot disease are a constant threat to at least 35 species of warm- and cool-season turfgrasses worldwide. Dollar spot is destructive, widespread and persistent, with more money spent on its control than any other turfgrass disease. Despite the global importance of dollar spot, until now scientists were unable to determine the identity of the fungus that causes the disease for over 80 years. This research used DNA criteria to show that dollar spot is caused by an entirely new and undescribed group of fungi, which was named Clarireedia. Scientists also discovered that at least four different species of the Clarireedia fungi cause dollar spot disease. Disease on cool-season grasses like Kentucky bluegrass and creeping bentgrass was caused by different Clarireedia fungi than what was found on warm-season grasses like bermuda grass and seashore paspalum. The scientists also found that dollar spot disease in the United Kingdom is caused by very different species of Clarireedia fungi than what is found elsewhere in the world. With this knowledge in hand, plant health practitioners, turfgrass breeders and producers now have the opportunity to develop disease control measures that are specifically targeted against the disease-causing agent.

Technical Abstract: Dollar spot is one of the most destructive and economically important fungal diseases of amenity turfgrasses. The causal agent was first described in 1937 as the ascomycete Sclerotinia homoeocarpa. However, the genus-level taxonomic placement of this fungus has been the subject of an ongoing debate for over 75 years. Existing morphological and rDNA sequence evidence indicates that this organism is more appropriately placed in the Rutstroemiaceae family rather than the Sclerotiniaceae. Here we use DNA sequence data from samples of the dollar spot fungus and other members of the Rutstroemiaceae (e.g. Rutstroemia, Lanzia, Lambertella) collected throughout the world to determine the generic identity of the turfgrass dollar spot pathogen. Phylogenetic evidence from three nucleotide sequence markers (CaM, ITS and Mcm7; 1810-bp) confirmed that S. homoeocarpa is not a species of Sclerotinia; nor is it a member of any known genus in the Rutstroemiaceae. These data support the establishment of a new genus, which we describe here as Clarireedia gen. nov. The type species for the genus, Clarireedia homoeocarpa comb. nov., is described to accommodate the dollar spot fungus, and a neotype is designated. Three new species in this clade, C. bennettii sp. nov., C. jacksonii sp. nov., and C. monteithiana sp. nov. that also cause dollar spot disease are described. Clarireedia homoeocarpa and C. bennettii occur primarily on Festuca rubra (C3 grass) hosts and appear to be restricted to the United Kingdom. Clarireedia jacksonii and C. monteithiana occur on a variety of C3 and C4 grass hosts, respectively, and appear to be globally distributed. This resolved taxonomy puts to rest a major controversy amongst plant pathologists and provides a foundation for better understanding the nature and biology of these destructive pathogens.