European Journal of Plant Pathology 107: 543–551, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. Nutritional enhancement of biocontrol activity of Candida sake (CPA-1) against Penicillium expansum on apples and pears Carla Nunes 1 , Josep Usall 1 , Neus Teixid´ o 1 , Miguel Mir ´ o 2 and Immaculada Vi˜ nas 1 1 Postharvest Unit, CeRTA, Centre UdL-IRTA, Av. Rovira Roure 177, 25198 Lleida, Catalonia, Spain (Phone: +34 973 702660; Fax: +34 973 238301; E-mail: nunes.carla@mail.telepac.pt); 2 Department of Food Technology, University of Lleida, Av. Rovira Roure 177, 25198 Lleida, Catalonia, Spain Accepted 4 April 2001 Key words: ‘Blanquilla’, biological control, blue mould, grey mould, Golden Delicious, postharvest Abstract Pome fruits are poor in nitrogenous compounds and the addition of nitrogen can improve colonisation of the fruits by antagonists. Twenty-two nitrogenous compounds were evaluated for their effect on Candida sake (CPA-1) growth in vitro. Ten compounds that induced greater growth were applied with the antagonist to wounded fruits to evaluate their effect on enhancing control of Penicillium expansum. Calcium chloride and 2-deoxy-d-glucose were also tested. l-serine and l-aspartic acid enhanced biocontrol by C. sake against P. expansum on apples. On apples and pears, ammonium molybdate, calcium chloride and 2-deoxy-d-glucose improved the capacity of the antagonist to control P. expansum. The addition of ammonium molybdate at 1 mM allowed C. sake to be used on apples and pears at a lower concentration without diminishing control. Similar results were observed with the addition of calcium chloride to the antagonist. 2-deoxy-d-glucose at 6 and 18 mM enhanced biocontrol on pears by over 81%, but on apples the improvement of biocontrol was observed only at 6 mM. In cold storage, the combination of ammonium molybdate and C. sake completely eliminated the incidence of blue mould on pears, and reduced its severity and incidence by more than 80% on apples. Abbreviations: cfu – colony forming units; MSM – minimum salt medium; NYDB – nutrient yeast dextrose broth; OD – optical density; PDA – potato dextrose agar; RH – relative humidity. Introduction Postharvest fruit and vegetable diseases continue to cause losses world-wide. Fungicides are a primary means of controlling postharvest diseases (Eckert and Ogawa, 1985). The use of chemical fungicides is becoming increasingly restricted because of concerns for the environment and for human health, and it is very expensive to develop new pesticides to overcome the resistance developed by pathogens. Biological control has advanced greatly during the last few years and microbial antagonists have been reported to control several postharvest diseases of fruits (Janisiewicz and Roitman, 1988; Janisiewicz and Marchi, 1992; Mercier and Wilson, 1994; Vi ˜ nas et al., 1998; 1999; Wilson and Wisniewski, 1994). Reliability and cost are two major factors that will determine the feasibility of any biocontrol system (Janisiewicz et al., 1992). Higher concentrations of the antagonist must be applied to achieve a more effective control (Janisiewicz, 1987; Pusey and Wilson, 1984), but increasing the antagonist populations makes bio- control less economical. However, epiphytic antag- onists are influenced by a number of biological and environmental factors (Blakeman and Fokkema, 1982; Fokkema 1984; Morris and Rouse, 1985), and storage practices. They also affect biocontrol and could be manipulated to enhance antagonist activity.