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Varying the cellulose component of coating formulations affected the survival of two yeast biocontrol agents, Candida guillermondii (Castelani) Langeron and Guerra strain US7 and Debaryomyces sp. strain 230, when these yeasts were incorporated into the coating. Using methylcellulose as the main film-former gave the most recovery of the yeasts after an incubation period for both strains. Significant control of decay on naturally infected `Pineapple' and `Valencia' oranges [Citrus sinensis (L.) Osb.] was demonstrated for US7 in a methylcellulose-based coating for the first 2 to 4 weeks of storage at 16C and 90% relative humidity. During this time, US7 in methylcellulose formulations was similar in decay control to a commercial shellac coating with imazalil at 2000 mg·liter–1. A US7 concentration of at least 105 colony-forming units/cm was maintained on the coated fruit surface of `Valencia' oranges for 3 weeks of storage. Suppression of decay by US7 was improved by the addition of glucose and calcium chloride to the coating formulation. Although nearly equal in concentration recovered, Debaryomyces strain 230 was not as effective as US7 in disease suppression of `Pineapple' oranges. The addition of US7 to Nature Seal, a coating material made with methylcellulose, had neither a quantitative nor a qualitative effect on the pathogen population compared to the same formulation without the antagonist. Chemical name used: 1-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl]-1H-imidazole (imazalil).

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