Losses from postharvest diseases of fruits have been substantial at the storage, wholesale, retail, and consumers levels. The total losses are very difficult to establish because research has generally considered only one or two levels, and little work has been done to determine losses at the consumer level. Nevertheless, in the United States, losses are estimated to range from 5% for citrus to as much as 20% for strawberries (Cappellini and Ceponis 1984; Eckert and Ogawa 1985). Most of the fruit decay results from infection through wounds made during harvest and postharvest handling, but for some fruits, infection takes place in the orchard during the growing season, and remains latent. As fruit mature in storage the pathogens become active again and invade fruit tissue. A variety of approaches have been used to reduce postharvest fruit decays, including sanitation to reduce pathogen inoculum, gentler handling of fruit to reduce wounding (Sommer 1982), physical treatments such as hot water dips and hot air treatments that kill pathogens (Falik et al. 1995; Lurie et al. 1998), storing produce at low temperatures or in modified atmosphere which stop or reduce growth of the pathogens (Sommer 1982), treating fruit with chemicals that enhance natural resistance (El-Ghaouth 1998), with synthetic fungicides (Eckert and Ogawa 1985; Eckert and Ogawa 1988), and, more recently, with biocontrol agents (Droby et al. 1998; Janisiewicz and Jeffers 1997; Janisiewicz and Korsten 2002; Korsten et al. 1995; Usall et al. 2001). Fungicides have been, by far, the most widely used remedy against fruit decay because they are easy to apply and generally, one fungicide is effective against most of the pathogens on a specific crop. Storage of some fruits for extended periods, e.g., citrus fruits, is totally dependent on the use of fungicides. But postharvest use of synthetic fungicides has been increasingly curtailed by the perceived hazard to humans and the environment. This has resulted in new regulations restricting or eliminating their use in this country and abroad. It has become increasing difficult to find and register new fungicides to replace those to which postharvest pathogens have developed resistance (Gullino and Kuijpers 1994; Ragsdale and Sisler 1994). Thus, there has been a need to find effective alternatives to synthetic fungicides. None of the alternative methods developed during the past two decades have had the broad spectrum of activity as synthetic fungicides. Recently, biological control has emerged as an alternative (Janisiewicz and Korsten 2002). The full potential of biocontrol has not yet been realized because the mechanisms of biocontrol have not been explained. A fuller understanding of the antagonistic mechanisms will eventually help manipulate and improve the biocontrol system. Although this method has some limitations, these limitations can be addressed by combining biological control with other alternative methods (Conway et al. 1999; El-Ghaouth et al. 2000b; Janisiewicz et al. 1998; Smilanick et al. 1999). In this chapter, the key elements in the development of biological control of postharvest diseases (BCPD) of fruits, and the current status and future prospects of BCPD of fruits using examples of fungal and bacterial antagonists are discussed.

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