Candidacolonium agrostis, a novel species associated with summer patch-like disease on Agrostis stolonifera in East China

Creeping bentgrass (Agrostis stolonifera) is one of the most preferred turfgrass species for putting greens at golf courses throughout China. In autumn 2020 and summer 2021, a summer patch-like disease was observed on creeping bentgrass putting greens at two golf courses in East China. Fungal isolates with similar morphology were consistently isolated from the dark root tissues. Four representative isolates from the two golf courses were identified through morphological, biological, and phylogenetic analyses. Bayesian methods and maximum likelihood were used to construct phylogenetic trees based on both multiple and single loci of partial sequences of the 18S nuc rDNA (SSU), ITS1-5.8S-ITS2 nuc rDNA internal transcribed spacer (ITS), and 28S nuc rDNA (LSU) regions, and of the largest subunit of RNA polymerase II (RPB1), minichromosome maintenance complex 7 (MCM7), and translation elongation factor 1-alpha (TEF1) genes, respectively. The isolates consistently formed a highly supported clade within the genus Candidacolonium, which was further supported by distinctive morphological characters. In pathogenicity tests, the fungus produced slightly lobed or mitten-shaped hyphopodia, colonized roots of creeping bentgrass via ectotrophic, dark runner hyphae, and caused disease symptoms with root discoloration, root and shoot mass reduction, and yellow leaf spots. This pathogenic fungus is described as a new species, Candidacolonium agrostis sp. nov., and is most likely the cause of a summer patch-like disease on creeping bentgrass in East China.