ARS | Publication request: Production of microsclerotia of the entomopathogenic fungus Metarhizium anisopliae in liquid culture

Submitted to: American Society for Microbiology
Publication Type: Abstract
Publication Acceptance Date: February 20, 2008
Publication Date: N/A

Technical Abstract: The goal of this study was the development of a liquid culture method for producing stable, infective propagules of the entomopathogenic fungus Metarhizium anisopliae for control of soil-dwelling insect pests. Three strains of M. anisopliae, F52, TM109, and MA1200, were evaluated using aerated, liquid cultures containing a basal salts medium supplemented with casamino acids and glucose to provide varying carbon concentrations and carbon-to-nitrogen (C:N) ratios. Under the conditions of this study, strain MA1200 produced significantly higher concentrations of blastospores when compared to the other two strains of M. anisopliae with highest blastospore concentrations of 1.6 and 4.2 x 108 blastospores ml-1 being produced by days 4 and 8, respectively. Microsclerotia (small sclerotial bodies, 200-600 microns in diameter) were produced by all three strains of M. anisopliae. The highest concentrations of microsclerotia, 2.7 and 2.9 x 108 L-1, were produced by M. anisopliae strain F52 grown in media with a high carbon concentration (36 g L-1) and C:N ratios of 30:1 and 50:1, respectively. Rehydration of air-dried microsclerotia on water agar plates resulted in 96-100% hyphal germination after 24 hours incubation at 28 C and sporogenic germination leading to the production of 5.3-11.4 x 108 conidia/g dried microsclerotia preparation after 168 hours incubation. Soil incorporation of air-dried microsclerotia preparations resulted in the production of high concentrations of M. anisopliae conidia in situ and significant mortality in sugarbeet root maggot Tetanops myopaeformis) larvae. While many plant pathogenic fungi produce sclerotia as overwintering structures, this study is the first report on the formation of sclerotial bodies by an entomopathogenic fungus. The development of a liquid culture method for producing high concentrations of stable, efficacious microsclerotia provides a novel approach for the control of soil-dwelling insects using sclerotial preparations of M. anisopliae.