Effect of drying on conidial viability of Penicillium frequentans, a biological control agent against peach brown rot disease caused by Monilinia spp.

The effects of drying methods (freeze-, spray-, and fluid bed-drying) on viability of Penicillium frequentans conidia were compared. Viability, estimated by germination of fluid bed- and freeze-dried conidia, was similar to that of fresh conidia. Skimmed milk alone, or in combination with other protectants, was added to conidia before freeze- drying. After the freeze- drying process, all protectants used, except glycerol improved conidial viability. Freeze-dried P. frequentans conidia did not maintain viability after 30 days of storage at room temperature, while conidia dried by fluid bed- drying showed 28% viability following 180 days after drying. This work also demonstrated a relationship between conidial viability after 1 year of storage at room temperature, moisture content after fluid bed- drying and initial weight of sample. Conidial moisture contents must be reduced to 5-15% for optimal storage at room temperature. P. frequentans conidia dried by fluid bed- drying were as effective as fresh conidia in controlling brown rot of peaches.