Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2014
Publication Date: 6/2/2014
Citation: Kepler, R.M., Humber, R.A., Rehner, S.A. 2014. Clarification of generic and species boundaries for Metarhizium and related fungi through multigene phylogenetics. Mycologia. 106(4)-811-829, DOI:10.3852/13-319.
Interpretive Summary: Insect parasitic fungi are used for the biological control of agricultural pest insects. Identification and classification of these fungi is complicated by their simple physical form, which makes these organisms hard to distinguish from one another. We performed a molecular analysis of the asexual insect pathogen Metarhizium to determine their relationship to other similar fungi. Using DNA sequences from five gene regions, we provide a detailed account of relationships in this group and change the definition of Metarhizium to include species of Metacordyceps and other genera. Two new species, M. brasiliensis and M. koreana are described. This research will be used by insect pathologists who need to identify these fungi when used to control agricultural pest insects.
Technical Abstract: The genus Metarhizium traditionally refers to green-spored asexual insect pathogenic fungi. Through culturing and molecular methods, Metarhizium has been linked to Metacordyceps sexual states. Historically, fungal nomenclature has allowed separate names for the different life-stages of pleomorphic fungi. However, with the move to one name for one fungus regardless of life-stage, there is a need to determine which name is the most appropriate. For Metarhizium the situation is complicated by the fact that Metacordyceps sexual states are interspersed among additional conidial genera, including Pochonia, Nomuraea and Paecilomyces. Metarhizium has priority as the earliest available name, but delimiting the boundaries of this genus remains problematic. Previous phylogenetic work identified a core Metacordyceps clade, comprised of strongly pigmented species including the asexual genera Metarhizium and Nomuraea, subtended by a poorly resolved grade of species lacking pigmentation and including asexual forms identified as Pochonia or formerly attributed to Paecilomyces. To clarify relationships among these taxa we have obtained representative material for each genus and established a molecular dataset of five protein-coding genes. The resulting phylogeny supports Metarhizium combining the majority of species recognized in Metacordyceps as well as the green-spored Nomuraea species and those in the more recently described genus Chamaeleomyces. Pochonia is polyphyletic, and we restrict the sense of this genus to those species forming a monophyletic clade with P. chlamydosporia, and the excluded species are transferred to Metapochonia gen. nov. It is our hope this unified concept of sexual and asexual states in Metarhizium will foster advances in understanding the unique ecologies of the associated species.