Production of the fungal biocontrol agent Epicoccum nigrum by solid substrate fermentation: effect of water activity on accumulation of compatible solutes

Epicoccum nigrum conidia were produced by solid fermentation on wheat grain s (cv. Rendeveaux and Brigadier) at different water activities (a(w)). Coni dial production was highest at high a(w) (0.996) than at reduced a(w) (0.98 ). However, conidial production at reduced a(w) was improved when the a(w) of the substrate was adjusted with a mixture of glycerol and water. Maximum levels of conidiation were 7-11 x 10(6) conidia g(-1) grain. The a(w) of t he solid substrate affected the pattern of accumulation of compatible solut es in the conidia. Mannitol was the main polyol in all conidial types. Howe ver, the amounts of mannitol were higher in conidia produced at high a(w). At reduced a(w) the conidia of E. nigrum accumulated more glycerol, which i s more efficient in the osmorregulation proccess than mannitol. Arabitol ac cumulated in low amounts, specifically in conidia produced at the lower a(w ), on cv. Rendeveaux but not on cv. Brigadier. Trehalose was detected in hi gher amounts in cv. Rendeveaux than in cv. Brigadier, and the amounts were higher in conidia produced at high a(w). A significant amount of endogenous solutes was detected in the washing liquid used for the separation of the conidia.