Systematic characterization of two Rosellinia species (subgenus Corrugata) causing disease on conifers in temperate forests of the United States

Authors: MILLER, STEPHAN - Oak Ridge Institute For Science And Education (ORISE); MUNCK, ISABEL - Forest Service (FS); Castlebury, Lisa

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Conifer trees in Maine, New Hampshire, and Ohio are known to host two different fungal species that are extremely difficult to tell apart. Both cause a disease called twig and needle blight, and there have been suggestions that they represent the same species. These fungi were given a preliminary microscopic identification and subjected to DNA analysis to determine their genetic relatedness. Even though there were some microscopic differences noted it was determined by using DNA sequences that the two likely represented a single species. The resulting DNA sequences were deposited in a public database and the microscopic features were captured by digital imaging. This important information will assist forestry professionals, plant pathologists and regulatory officials in the management and tracking of conifer and other forest tree diseases and lead to less confusion about the pathogen causing twig and needle blight.

Technical Abstract: In 2023, conifers with Rosellinia infections were discovered in Maine, New Hampshire, and Ohio. The trees displayed twig and needle blight with heavy matting of mycelium on plant samples. Based on morphological characterization, the isolates causing the infections were identified as either Rosellinia mycophila or R. herpotrichoides. Both species belong to the R. thelena subgroup (subgenus Corrugata) of Rosellinia as defined by Petrini (2013). To date, no molecular data are available for species within the Corrugata subgenus; we sequenced and conducted a multi locus phylogenetic analysis (ITS, LSU, TUB2, RPB2) with the collected specimens. Recently, several Rosellinia species were segregated to Dematophora as they cluster in a separate clade and form distinct asexual morphs; Rosellinia species form geniculosporium-like conidiogenous cells while Dematophora species form dematophora-like asexual cells. The research conducted herein reveals that R. mycophila and R. herpotrichoides form a well-defined clade which neighbors the geniculosporium and dematophora-like clades. Both R. mycophila and R. herpotrichoides produce nodulisporium-like conidiogenous cells. It is likely that other Rosellinia species forming a nodulosporium-like anamorph cluster in this clade. Based on evolutionary divergence values, the R. mycophila and the R. herpotrichoides specimens collected in this study are more than 99.3% similar. In 1961, Petrak considered R. mycophila to be a small-ascospore form of R. herpotrichoides. In 1986, Francis disagreed and argued that the two should be maintained as separate species. Our analysis suggests there is little genetic distinction between the two species from our field collections; the differences in ascospore morphology may reflect phenotypic plasticity and environmental variation.