Differential Induction of Proteins in Orange Flavedo by Biologically Based Elicitors and Challenged by Penicillium digitatum Sacc. 1 J. E. Fajardo, T. G. McCollum, R. E. McDonald, and R. T. Mayer U.S. Horticultural Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 2120 Camden Road, Orlando, Florida 32803-1419 E-mail: mcdonald@ao.net Received June 16, 1997; accepted August 20, 1998 The effects of biologically based inducing agents (elicitors) applied singly or in combination to har- vested oranges were investigated for enhancing host resistance to green mold. Oranges (Citrus sinensis cv. ‘Valencia’) treated with inducing agents and chal- lenged by the green mold pathogen (Penicillium digita- tum) showed a delay in the onset and progression of disease symptoms compared with inoculated fruits not treated with the elicitors. Chitosan (a preparation of ground crab shells), Margosan-O (an oil-based plant- derived product from neem seed)  Aspire (a water dispersible granule containing an antagonistic yeast), Aspire, and chitosan  Aspire reduced fruit decay 38, 41, 42, and 44%, respectively. The inducing agents reduced disease incidence but not disease severity. Application of elicitors followed by inoculation with P. digitatum and P. digitatum infection alone in- creased total soluble proteins in the flavedo (the tissue that forms the outer colored rind) twofold relative to the untreated control. The flavedo is an important tissue that is vulnerable to postharvest diseases espe- cially at storage and transport of the harvested crop. No apparent qualitative differences were visualized in protein patterns analyzed by SDS–PAGE of all treat- ments across all days of incubation. A temporal differ- ential induction of chitinase, -1,3-glucanase, and per- oxidase was demonstrated as a result of elicitor application followed by challenge inoculation with P. digitatum. Induction of these enzymes was corrobo- rated by immunodetection. Lysozyme and a polygalac- turonase-inhibiting protein were detected at low activ- ity levels. However, the defensive proteins appeared to be constitutive and slightly induced but did not in- volve the de novo synthesis of novel proteins. Key Words: Azadirachta indica; Candida oleophila; green mold; induced resistance; neem extract; yeast. INTRODUCTION About 25% of the economic loss in harvested fruits and vegetables is caused by pathogens during harvest- ing, processing, packing, and transporting of the com- modity (Wilson and Wisniewski, 1989; Droby et al., 1991; Wisniewski and Wilson, 1992). Green mold, caused by Penicillium digitatum Sacc. is an important posthar- vest disease of citrus (Whiteside et al., 1993). Control of green mold is mostly by the use of fungicides such as benomyl, imazalil, and thiabendazole. Development of fungicide-resistant strains of P. digitatum has occurred and no new fungicides are currently being used (Eckert and Wild, 1983). The use of biologically based materials for the control of postharvest diseases may help combat fungicide-resistant strains of pathogens (Spotts and Cervantes, 1986; Holmes and Eckert, 1992; Stange and Eckert, 1994; Brown, 1995), avoid pesticide residues from the environment and commodities (Brown, 1995), reduce cost of disease control (Brown, 1995), minimize effects on nontarget organisms (Droby et al., 1991), and circumvent regulatory and environmental issues im- pacting registration of chemicals (Wisniewski and Wil- son, 1992; Brown, 1995). Alternatives to synthetic chemicals that are of poten- tial use in postharvest disease control include antago- nistic microorganisms, natural plant- and animal- derived products with fungicidal properties, and induced resistance (Wilson and Wisniewski, 1989; El Ghaouth, 1994; Wilson et al., 1994). The use of biologically based pesticides in conjunction with induced resistance was suggested as a feasible approach for reducing posthar- vest disease in harvested fruits and vegetables (Brown, 1989; Wilson and Wisniewski, 1989; Droby et al., 1991; El Ghaouth, 1994; Wilson et al., 1994). Induction of constitutive plant enzymes or pathogenesis-related (PR) proteins which are capable of inhibiting pathogen development would contribute to greater resistance. Induction can be triggered by elicitors that are biologi- cal, chemical, molecular, or physical (El Ghaouth, 1994). Elicitors can be used for the exploitation of defense mechanisms in plants by either directly acting as 1 Mention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the U.S. Department of Agricul- ture and does not imply its approval to the exclusion of other products or vendors that may also be suitable. BIOLOGICAL CONTROL 13, 143–151 (1998) ARTICLE NO. BC980661 143 1049-9644/98