Colletotrichum species cause anthracnose diseases on a number of grass hosts and are common inhabitants of many others. They are divided into four species: C. sublineolum is pathogenic to Sorghum spp.; C. caudatum is found on C4 grasses such as indiangrass and big bluestem; C. falcatum causes red rot of sugarcane; and C. graminicola sensu lato is a broadly defined species including isolates that attack maize, wheat, oats, and many forage, turf, and amenity grasses of the subfamily Pooideae. In this paper, a combination of hierarchal- and nonhierarchal-based analyses were employed to examine evolutionary relationships among the grass-infecting Colletotrichum species, with special emphasis on isolates from turf and other grasses in the subfamily Pooideae. Reconstructions performed with data sets from over 100 Colletotrichum isolates at three variable loci using phylogenetic and network-based methodologies unambiguously supported the taxonomic separation of maize-infecting isolates of C. graminicola from the pooid-infecting strains of Colletotrichum. To reflect the evolutionary relationships that exist between these distinct lineages, we propose the resurrection of the species name C. cereale to describe the pooid-infecting isolates. There was also support for further subdivision of C. cereale, but the current data are insufficient to confidently subdivide the species, as there was some evidence of recombination between lineages of this species.

In 1989, a close association was found between single-plant progenies of strong creeping red fescue infected with the endophyte Epichloë festucae and enhanced suppression of dollar spot, a widespread foliar disease of turfgrass caused by Sclerotinia homoeocarpa. From this limited observation, extensive field evaluations were conducted on a wide range of fine fescue germplasm obtained throughout the United States and Europe to determine the frequency and magnitude of this association. In five field trials established between 1985 and 1991, endophyte-infected Chewings, hard, blue, and strong creeping red fescue cultivars, selections, and crosses consistently exhibited endophyte-mediated suppression of dollar spot, when compared with closely related endophyte-free entries. Endophyte-infected Chewings and hard fescue cultivars and selections also had greater turf density and supported less foliar mycelium of S. homoeocarpa than endophyte-free entries.

Frequency and severity of anthracnose epiphytotics, caused by Colletotrichum cereale Manns Manns sensu lato Crouch, Clarke, and Hillman, on annual bluegrass (ABG) [Poa annua L. f. reptans (Hauskins) T. Koyama] putting greens have increased over the past decade. This 3‐yr field study evaluated the impact of N fertilization (4.9 kg ha−1 every 7 or 28 d), mefluidide (ME; 0 and 0.106 kg a.i. ha−1 yr−1) {N‐[2,4‐dimethyl‐5‐[[(trifluoromethyl)sulfonyl]amino]phenyl]acetamide}, trinexapac‐ethyl (TE; 0 and 0.050 kg a.i. ha−1 every 14 d) [4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxocyclohexanecarboxylic acid ethylester], verticutting (VC; 0‐ and 3‐mm depth every 14 d), and interactions of these factors on anthracnose of ABG mowed at 3.2 mm. Nitrogen fertilization frequency had the greatest influence on disease throughout the study; N applied at 4.9 kg ha−1 every 7 d reduced damage 5 to 24% compared to a 28‐d interval. The plant growth regulators, ME and TE, frequently interacted during the last 2 yr of the study; sequential application of ME and TE reduced disease 6 to 14% compared to plots that only received one of these plant growth regulators. At advanced stages of disease, the combination of 7‐d N fertilization and ME and TE application had the greatest disease reduction. Verticutting had little effect on anthracnose severity.

Species limits in the fungal genus Colletotrichum are traditionally distinguished by appressorial and/or conidial morphology or through host plant association, but both criteria are criticized for their inability to resolve distinct taxa. In previous research eight novel falcate-spored Colletotrichum species were identified from graminicolous hosts using multilocus molecular phylogenetic analysis. In the present work formal descriptions and illustrations are provided for six of the new taxa: C. hanaui sp. nov., C. nicholsonii sp. nov., C. paspali sp. nov., C. jacksonii sp. nov., C. miscanthi sp. nov. and C. axonopodi sp. nov.; and an emended description with epitypification is provided for C. eleusines. Comparison of hyphopodial appressoria and host association against phylogenetic species boundaries and evolutionary relationships in the graminicolous Colletotrichum group demonstrate that, while these characters can be useful in combination for the purpose of species diagnosis, erroneous identification is possible and species boundaries might be underestimated if these characters are used independently, as exemplified by the polyphyletic taxa C. falcatum. Appressoria have been subject to convergent evolution and were not predictive of phylogenetic relationships. Despite these limitations, the results of this work establish that in combination appressorial and host range characters could be used to generate informative dichotomous identification keys for Colletotrichum species groups when an underlying framework of evolutionary relationships, taxonomic criteria and nomenclature have been satisfactorily derived from molecular systematic treatments.

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 y. Existing morphological and rDNA sequence evidence indicates that this organism is more appropriately placed in the family Rutstroemiaceae 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, Clarireedia bennettii sp. nov., Clarireedia jacksonii sp. nov., and Clarireedia 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.