Development of a fluid-bed coating process for soil-granule-based formulations of Metarhizium brunneum, Cordyceps fumosorosea or Beauveria bassiana

Aim: Granule-based products of solid state fermented micro-organisms are available for biocontrol. Because liquid fermentation has several advantages, we investigated fluid-bed coating with liquid fermented biomass.

Methods and results: Biomass containing mycelium or mycelium and submerged spores of the entomopathogenic fungi Metarhizium brunneum, Cordyceps fumosorosea and Beauveria bassiana were produced in liquid culture, separated and different biomass concentrations were adjusted. Based on the examined thermo-tolerance, we defined fluid-bed coating adjustments and investigated granule colonization and sporulation on granules. Granule colonization depended on the biomass concentration and strain. For C. fumosorosea and B. bassiana, concentrations of 0·003%_{dry weight} resulted in nearly 100% granule colonization, for M. brunneum with concentrations of 0·7%_{dry weight} in only 50%. The conidiation on granules in sterile soil was highly influenced by the moisture content. Because the granule colonization of M. brunneum was unsatisfactory, we pre-coated nutrients followed by coating with biomass, submerged spores or conidia. Malt extract had a positive effect on the granule colonization for biomass and submerged spores. Furthermore, aerial conidia can also be coated.

Conclusions: Fluid-bed coating of fungal biomass is suitable for the development of granules.

Significance and impact of this study: With this technology, cost-efficient biocontrol products can be developed.