Production of Ampelomyces quisqualis conidia in submerged fermentation and improvements in the formulation for increased shelf-life

Abstract

A strain of Ampelomyces quisqualis (ITA3) was found to be more effective against powdery mildew than the commercial one (CNCM I‒807), however its mass production and formulation need to be developed for practical application as biopesticide. Strains of A. quisqualis are considered to be slow growing fungi with a radial growth rate of a few millimetres a week on solid media and their conidia are known to be difficult to produce in industrial fermenters. The current study optimised nutrient composition and growth conditions for high mycelial growth and conidiation of the ITA3 strain on a cost-effective culture medium and finalised a stable and effective dry formulation for the conidia. Plackett–Burman design and response surface methodology were employed for optimisation of new bioprocesses. In the tested culture media, a 23.2-fold increase in biomass and a 2.2 × 108 conidia yield were obtained with the optimised sugar-based medium, with a time reduction of 43% as compared to original sugar-based medium. The kinetic parameter biomass yield (Yx/s) and specific growth rate (μ) values obtained were 3.29 g cells g−1 substrate and 0.56 days−1, respectively. When fermentation was scaled-up in a fermenter, 3.8 × 107 conidia mL−1 were produced within 15 days. Silica gel powder added to undried conidia in water allowed good storage stability and preserved the biocontrol efficacy of the fungus. The high conidia yield and good biocontrol results achieved in this study with formulated ITA3 conidia are economically sustainable for the industrial production of A. quisqualis.