Population dynamics of postharvest decay antagonists growing epiphyticallyand within wounds on grapefruit

Coating formulations of shellac, sucrose ester, and cellulose were tested t hat support populations of bacterial and yeast antagonists of post-harvest Penicillium decay of grapefruit. Surface populations of Pseudomonas syringa e, P. fluorescens, and P. patida were stable between Id and 10(4) CEU/cm(2) on shellacked fruit over 4 months at 13 degreesC, hut numbers of the yeast Candida oleophila rose steadily from 2.35 x 10(3) to nearly 10(5). Through the first 15 days of cold storage, surface populations of P. syringae and C. oleophila were greater when applied to fruit within the pH 7.2 shellac t han when applied by dipping fruit into an antagonist suspension and drying the fruit prior to shellacking; numbers were generally equivalent thereafte r. Within wounds of shellacked fruit, populations of P. syringae were equal regardless of the method of application and increased from 10(4) to more t han 1.2 x 10(7) CFU within 2 weeks. In contrast, numbers of C. oleophila in wounds over the first 2 weeks of storage were greater in fruit dipped and coated with shellac than when the antagonist was incorporated in this mater ial; populations stabilized at approximate to6 x 10(6) CFU after 2 weeks. I ncorporation of P. syringae and C. oleophila into ester and cellulose coati ngs, however, initially fostered greater numbers of both antagonists in wou nds (approximate to 10(6) CFU) than did the preliminary dip application, an d significant population differences persisted for several weeks. In cold s torage, although application method did not affect the efficacy of P. syrin gae, C. oleophila was more efficacious after 3 and 4 months when applied in the shellac than when applied by a preliminary immersion and subsequent dr ying of fruit prior to shellacking.