Optimization of culture medium for microsclerotia production by Nomuraea rileyi and analysis of their viability for use as a mycoinsecticide

Microsclerotia (MS) formation was successfully induced in Nomuraea rileyi (Ascomycetes: Hypocreales) in liquid amended medium (AM) culture. To improve MS production, the culture medium was varied. Three quantitative variables, carbon, nitrogen, and basal salt sources, were investigated using the AM. An orthogonal experiment [L9 (3)3] design was applied to optimize the culture medium. Maximum MS production (21.9 × 104 MS ml−1) was obtained using the optimized culture medium (32.0 g l−1 of glucose, 2.0 g l−1 of ammonium citrate, and 0.15 g l−1 of ferrous sulfate). Subsequently, viability, including thermotolerance, shelf-life, and infection, were investigated to evaluate the potential of MS for use as a mycoinsecticide. The MS, collected from the optimized culture medium, exhibited virulence and greater thermotolerance than conidia, and maintained 86.4 % germinability after one-year room temperature storage. These results suggested that the MS obtained through optimization production can be used as a mycoinsecticide.