Biomass and Spore Yield of Cercospora aff. canescens by Submerged Fermentation: Defining and Optimizing Culture Conditions.

Morningglory species (Ipomoea spp.) are important weeds in Brazilian agriculture, particularly in non-burning sugarcane farming system. The fungus Cercospora aff. canescens has been selected as potential mycoherbicide; however, inoculum production is considered a challenge. The purpose of this study was to define and optimize culture conditions for biomass and spore yield of Cercospora aff. canescens CMAA 1444 in submerged fermentation. Initially, a Plackett-Burman experimental design with 12 treatments was conducted using a modified Czapek-Dox medium to screen the effect of these factors: carbon (dextrose): nitrogen (calcium nitrate) ratios (10:1, 50:1, and 100:1), pH (4, 7, and 8.5), light periods (0 = continuous dark, 12 h, and 24 h), magnesium sulphate (0.25 g.L- 1, 1 g.L- 1, and 2.5 g.L- 1) and potassium sulphate (0.25 g.L- 1, 1 gL- 1, and 2.5 g.L- 1) concentrations. Afterwards, individual assays were conducted in a completely randomized design using a broader range of C: N ratios (0:1; 20:1; 40:1; 60:1; 80:1; 100:1) and pH (3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8; 8.5, and 9). Highest biomass and spore yield were obtained after 14 days of submerged fermentation. Optimal conditions shared by both responses included 24-h light period, magnesium sulphate at 0.25 g.L- 1, and potassium chloride at 0.25 g.L- 1. Maximum biomass (3.0 g) was achieved at C: N ratio 100:1 and pH = 8.5, whereas maximum spore yield (8.4 × 105 spores.mL- 1) was achieved at C: N ratio 40:1 and pH = 5. These results represent an important step toward large-scale production of Cercospora aff. canescens, enabling its use as a mycoherbicide for the control of morningglories.