Commercial production of conidia emitting granules for soil application of Metarhizium brunneum

Abstract: Metarhizium brunneum Cb15 was produced in liquid culture and formulated into an extruded granule for controlling wireworms (Agriotes sp.) in potatoe-fields by applying the granules at planting. The production was optimized by changing the production medium for the fungus. Best conidia emission of resulting granules was achieved in media where the highest concentration of submerged conidia was produced. More submerged conidia were produced if the liquid culture was inoculated with aerial conidia than if started from a liquid preculture with submerged conidia. In the full grown fermentation broth a concentration of 5e7 submerged conidia/ml was achieved. The granules were produced directly from the fermentation broth by adding soy-flour, glucose, potassium-mono-phosphate and sodium-alginate. The resulting granules were dried at 45 °C inlet – and max. 38 °C outlet temperature to a residual moisture of approx. 7%. Conidia production of the resulting granules was tested on water agar. While 100% of the granules produced aerial conidia after 10 days incubation at16 °C, the concentration of conidia was 4.2e9 ± 7e8 conidia per g granules. The method for producing these conidia emitting granules is highly efficient and can eassily be adapted to other entomopathogenic or disease suppressing fungi.