Morphological and phylogenetic resolution of Conoideocrella luteorostrata (Hypocreales: Clavicipitaceae), a potential biocontrol fungus for Fiorinia externa in United States Christmas tree production areas

ABSTRACT

The entomopathogenic fungus Conoideocrella luteorostrata has recently been implicated in natural epizootics among exotic elongate hemlock scale (EHS) insects in Christmas tree farms in the eastern United States. Since 1913, C. luteorostrata has been reported from various plant feeding Hemiptera in the southeastern United States, but comprehensive morphological and phylogenetic studies of U.S. populations are lacking. The recovery of multiple strains of C. luteorostrata from mycosed EHS in North Carolina provided an opportunity to conduct pathogenicity assays and morphological and phylogenetic studies to investigate genus- and species-level boundaries among the Clavicipitaceae. Pathogenicity assays confirmed that C. luteorostrata causes mortality of EHS crawlers, an essential first step in developing this fungus as a biocontrol. Morphological studies revealed that conidia aligned with previous measurements of the Paecilomyces-like asexual state of C. luteorostrata, with conidiophore morphology consistent with historical observations. Additionally, a Hirsutella-like synanamorph was observed in select C. luteorostrata strains. In both a four-locus, 54-taxon Clavicipitaceae-wide phylogenetic analysis including D1–D2 domains of the nuclear 28S rRNA region (28S), elongation factor 1 alpha (EF1-α), DNA-directed RNA polymerase II subunit 1 (RPB1), and DNA-directed RNA polymerase II subunit 2 (RPB2) and a two-locus, 38-taxon (28S and EF1-α) phylogenetic analysis, all three Conoideocrella species were resolved as strongly supported monophyletic lineages across all loci and both methods (maximum likelihood and Bayesian inference) of phylogenetic inference except for 28S for C. tenuis. Despite the strong support for individual Conoideocrella species, none of the analyses supported the monophyly of Conoideocrella with the inclusion of Dussiella. Due to the paucity of RPB1 and RPB2 sequence data, EF1-α provided superior delimitation of intraspecies groupings for Conoideocrella and should be used in future studies. Further development of C. luteorostrata as a biocontrol against EHS will require additional surveys across diverse Hemiptera and expanded pathogenicity testing to clarify host range and efficacy of this fungus.

KEYWORDS:

• Paecilomyces cinnamomeus
• Torrubiella luteorostrata
• Dussiella tuberiformis
• elongate hemlock scale
• entomopathogenic fungus

ACKNOWLEDGMENTS

We acknowledge that this work was completed on the traditional land of the Osage, Shawnee, and Massawomeck peoples. Samples were additionally collected on the land of Cherokee, Yuchi, and Moneton peoples. We especially thank Ryan Percifield, Director of the West Virginia University Genomics Core Facility, who assisted with library preparation and sequencing of C. luteorostrata strain ARSEF 14590.

DISCLOSURE STATEMENT

JES was a paid consultant for Zymergen, Sincarne, and Michroma.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00275514.2023.2296337

Additional information

Funding

This project was funded by the Christmas Tree Promotion Board grants 20-10-WVU and 21-07-WVU. B.L. was supported by the U.S. Department of Agriculture (USDA-ARS Project 8062-22410-007-000D). H.B. was supported by West Virginia University (WVU) Research Apprentice Program, and the Honors Biology Capstone Program, under Dr. Susan Raylman in the WVU Department of Biology. A.M.M. was supported by a WVU Outstanding Merit Fellowship. J.E.S. is a Canadian Institute for Advanced Research (CIFAR) fellow in the program “Fungal Kingdom: Threats and Opportunities” and was supported by the National Science Foundation (NSF) (EF-2125066) and the U.S. Department of Agriculture (USDA) (National Institute of Food and Agriculture Hatch project CA-R-PPA-211-5062-H). Analyses were performed on the University of California Riverside High Performance Computing Cluster supported by the NSF (DBI-1429826 and DBI-2215705) and the National Institutes of Health (NIH) (S10-OD016290).