Diversity of rhizosphere associated entomopathogenic fungi of perennial herbs, shrubs and coniferous trees

Understanding habitat selection of fungal entomopathogens is critical to improve the efficacy, persistence and cost of these fungi as microbial insecticides. This study sought to determine the prevalence of Metarhizium and Beauveria spp. isolated from the rhizosphere of strawberry, blueberry, grape and Christmas tree crops in the Willamette Valley of Oregon. Entomopathogenic fungi were assigned to thirteen species based on molecular phylogenetic criteria. Four species of Metarhizium were isolated including Metarhizium brunneum, Metarhizium guizhouense, Metarhizium robertsii, and Metarhizium flavoviride var. pemphigi. Nine Beauveria species were isolated including, Beauveria brongniartii, an undescribed species referred to as Clade C and seven phylogenetic species of Beauveria bassiana. Strawberries and blueberries were significantly associated with M. brunneum and Christmas trees with M. guizhouense and M. robertsii. Grapes were significantly associated with B. bassiana phylogenetic species Bbas-16. All of the Metarhizium isolates screened were pathogenic to Otiorhynchus sulcatus larvae in laboratory bioassays but only M. brunneum and M. robertsii caused significant levels of infection. The study results suggest that certain species of Metarhizium and Beauveria are significantly associated with the strawberry, blueberry and Christmas tree rhizosphere and could potentially provide better control of O. sulcatus.

Graphical abstractMaximum parsimony phylogeny of tef 1 sequences of Metarhizium isolates and Bloc gene sequences of Beauveria isolates. Bootstrap analysis was based on 1000 pseudo-replicates; bootstrap values ⩾70% are listed above relevant internodes. Scale bar represents five nucleotide changes. Representative sequences are available from GenBank under accession HQ412787–HQ412795 and HQ412773–HQ412786, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Four species of Metarhizium were isolated including M. brunneum, M. guizhouense, M. robertsii, and M. flavoviride var. pemphigi. ► Nine Beauveria species were isolated including, Beauveria brongniartii, an undescribed species referred to as Clade C and seven phylogenetic species of Beauveria bassiana. ► Strawberries and blueberries were significantly associated with M. brunneum and Christmas trees with M. guizhouense and M. robertsii. ► Grapes were significantly associated with B. bassiana phylogenetic species Bbas-16.