Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2009
Publication Date: 8/1/2009
Citation: Jackson, M.A., Jaronski, S.T. 2009. Production of Microsclerotia of the Fungal Entomopathogen Metarhizium anisopliae and their Use as a Biocontrol Agent for Soil-Inhabiting Insects. Mycological Research. 113(8):842-850.
Interpretive Summary: The formation of a sclerotium, an overwintering structure produced by many plant pathogenic fungi, has not been reported for any entomopathogenic fungi, including Metarhizium anisopliae. Three strains of M. anisopliae all formed desiccation tolerant microsclerotia (small sclerotia) using deep-tank fermentation. Microsclerotia of M. anisopliae survived drying (less than 5% moisture) with no significant loss in viability. Rehydration and incubation of air-dried microsclerotia of M. anisopliae on moistened soils resulted in filamentous growth and the production of insect-infecting spores. When incorporated in soil, microsclerotia of M. anisopliae infected and killed the sugar beet root maggot, Tetanops myopaeformis. This is the first report of the production of sclerotia by an entomopathogen using deep-tank fermentation and provides a novel approach to the control of soil-dwelling insects with the biocontrol fungus, M. anisopliae.
Technical Abstract: Three strains of Metarhizium anisopliae, F52, TM109, and Ma1200, were evaluated for growth and propagule formation in shake flask studies using media with varying carbon concentrations and carbon-to-nitrogen ratios. Under the conditions of this study, all strains produced blastospores and microsclerotia, a pigmented, compact hyphal aggregate. The formation of a microsclerotium, an overwintering structure produced by many plant pathogenic fungi, is novel for entomopathogens, including M. anisopliae. The three strains of M. anisopliae tested produced similar biomass concentrations when media and growth time were compared. Strain Ma1200 produced significantly higher concentrations of blastospores when compared to the other two strains of M. anisopliae with highest blastospore concentrations (1.6 and 4.2 x 108 blastospores ml-1 on days 4 and 8, respectively) produced in media with the highest carbon and nitrogen concentrations. While all strains formed desiccation tolerant microsclerotia, highest concentrations were produced by strain F52 in carbon-rich media. Microsclerotial preparations of M. anisopliae survived drying (less than 5% moisture) with no significant loss in viability. Rehydration and incubation of air-dried microsclerotia on water agar plates resulted in hyphal and sporogenic germination to produced high concentrations of conidia. Bioassays with the sugarbeet root maggot, Tetanops myopaeformis, where dried microsclerotial preparations of M. anisopliae strain F52 were incorporated into soil, showed significant efficacy in controlling the insect even in drier soils. Microsclerotial preparations of M. anisopliae F52 showed superior efficacy against the sugarbeet root maggot were compared to conventional conidia-containing corn grit granules. This is the first report of the production of sclerotial bodies by an entomopathogen and provides a novel approach to the control of soil-dwelling insects with M. anisopliae.