Effect of drying on conidial viability of Penicillium frequentans , a biological control agent against peach brown rot disease caused by Monilinia spp. BELEN GUIJARRO, INMACULADA LARENA, PALOMA MELGAREJO, & ANTONIETA DE CAL Department of Plant Protection, INIA, Madrid, Spain (Received 31 January 2005; returned 28 March 2005; accepted 26 July 2005) Abstract 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. Keywords: Biological control, brown rot disease, fluid bed-drying, Monilinia spp., Penicillium frequentans Introduction Penicillium frequentans Westling, a component of the resident mycoflora of peach twigs and flowers (Melgarejo et al. 1985), reduces peach twig blight caused by Monilinia laxa (Aderh. et Ruhl.) Honey (Melgarejo et al. 1986; De Cal et al. 1990). P. frequentans induced significant reductions in disease severity (from 38 to 80%) compared to the fungicide captan (De Cal et al. 1990) when it was included in some preparations. Recently, De Cal et al. (2002) have developed a mass production method for P. frequentans conidia by solid-fermentation. Biological control agents must be formulated as products capable of storage, distribution and application in the agricultural market to be of practical use. The major drawback in commercialising biocontrol products is the development of stable formulated products that retain similar efficacy to that of the agent’s fresh cells Correspondence: P. Melgarejo, Department of Plant Protection, INIA, Crtra. De la Corun ˜a Km. 7, 28040 Madrid, Spain. Tel: 34 91 3476846. Fax: 34 91 3572293. E-mail address: melgar@inia.es First published online 24 January 2006 ISSN 0958-3157 print/ISSN 1360-0478 online # 2006 Taylor & Francis DOI: 10.1080/09583150500335897 Biocontrol Science and Technology, 2006; 16(3/4): 257  /269