Drying of conidia of Penicillium oxalicum, a biological control agent against Fusarium wilt of tomato

The effects of freeze drying, spray drying, and fluid bed drying on the viability of Penicillium oxalicum conidia were compared. Conidia of P. oxalicum can be dried by fluid bed drying and freeze drying maintaining 100% viability after both processes, but protective additives must be added for obtaining this viability in the case of freeze drying. The best viabilities were obtained after freeze drying with non-fat skim milk (NFSM) + Tween 20, NFSM + peptone and NFSM + sucrose. However, NFSM + glycerol had only a 0.5% viability after freeze drying. Freeze-dried P. oxalicum conidia with or without additives did not maintain viability over time at room temperature, while conidia dried in a fluidized bed drier had a 40-50% viability after 180 days of storage in these conditions. Penicillium oxalicum conidial viability after spray-drying was lower than 20%. Penicillium oxalicum conidia dried by fluid bed drying were effective in reducing the incidence of Fusarium wilt of tomato under glasshouse and field conditions.