Shellac formulations to reduce epiphytic survival of coliform bacteria on citrus fruit postharvest.

Survival of the coliform bacteria Enterobacter aerogenes and Escherichia coli was monitored in a neutral carboxymethylcellulose formulation and in shellac formulations with various pH and concentrations of ethanol and the preservative paraben; populations were subsequently measured from the surface of citrus fruit coated with these formulations. Numbers of the two bacteria increased over 24 h from 10(6) CFU/ml to approximately 10(8) CFU/ml in the carboxymethylcellulose solution, but over this time numbers remained little changed in the neutral solution of shellac. The Enterobacter was more tolerant of alcohol over a 3-h period: although its numbers in a shellac solution with 10% ethanol dropped from more than 10(6) CFU/ml to just over 10(3) CFU/ml. E. coli and a third species. Klebsiella pneunoniae, declined toward the limit of detection (5 CFU/ ml) during this time. The addition of morpholine to increase the formulation pH to 9.0 caused numbers of bacteria to plummet to an undetectable level within 30 to 60 min. On Ruby Red grapefruit and Valencia oranges in storage at 13 degrees C numbers of E. aerogenes and E. coli declined over 2 weeks from 10(5) CFU/cm2 to less than 2.5 x 10(1), but most of the loss in numbers occurred within 1 day. Numbers remained significantly less on shellacked fruit compared with those applied in the carboxymethylcellulose coating, and a shellac coating prepared from a pH 9 solution was more toxic to these species than one in which 12% ethanol had been added to the neutral formulation. The addition of the preservative paraben in the basic shellac was further inhibitory.

Hot water treatment and insecticidal coatings for disinfesting limes of mealybugs (Homoptera: Pseudococcidae).

Hot water immersion and insecticidal coatings were tested to determine if they could be used to disinfest Persian limes, Citrus latifolia Tanaka, of the mealybug pests Planococcus citri Risso and Pseudococcus odermatti Miller & Williams. A 20-min 49 degrees C hot water immersion treatment is effective in killing mealybugs and all other arthropods tested found externally on limes, or under the calyx. No insects or mites were found to survive after the 20-min hot water treatment. In this test, 7,200 limes were treated with 1,308 insects killed and zero survivors. Treatment at 49 degrees C for 20 min did not significantly affect quality when treated fruit were compared with untreated control fruit. Four coatings were tested at a 3% rate: two petroleum-based oils (Ampol and Sunspray oil), a vegetable oil (natural oil), and a soap (Mpede). The coatings gave up to 94% kill (Ampol) of mealybugs, which is not sufficient to provide quarantine security. The coatings might be effective as a postharvest dip before shipment.

Population dynamics of postharvest decay antagonists growing epiphytically and within wounds on grapefruit.

ABSTRACT Coating formulations of shellac, sucrose ester, and cellulose were tested that support populations of bacterial and yeast antagonists of postharvest Penicillium decay of grapefruit. Surface populations of Pseudomonas syringae, P. fluorescens, and P. putida were stable between 10(3) and 10(4) CFU/cm(2) on shellacked fruit over 4 months at 13 degrees C, but 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 than when applied by dipping fruit into an antagonist suspension and drying the fruit prior to shellacking; numbers were generally equivalent thereafter. Within wounds of shellacked fruit, populations of P. syringae were equal regardless of the method of application and increased from 10(4) to more than 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 material; populations stabilized at approximately 6 x 10(6) CFU after 2 weeks. Incorporation of P. syringae and C. oleophila into ester and cellulose coatings, however, initially fostered greater numbers of both antagonists in wounds ( approximately 10(6) CFU) than did the preliminary dip application, and significant population differences persisted for several weeks. In cold storage, although application method did not affect the efficacy of P. syringae, C. oleophila was more efficacious after 3 and 4 months when applied in the shellac than when applied by a preliminary immersion and subsequent drying of fruit prior to shellacking.

Polygalacturonase Production by Agrobacterium tumefaciens Biovar 3.

Agrobacterium tumefaciens biovar 3 causes both crown gall and root decay of grape. Twenty-two Agrobacterium strains representing biovars 1, 2, and 3 were analyzed for tumorigenicity, presence of a Ti plasmid, ability to cause grape seedling root decay, and pectolytic activity. All of the biovar 3 strains, regardless of their tumorigenicity or presence of a Ti plasmid, caused root decay and were pectolytic, whereas none of the biovar 1 and 2 strains had these capacities. Isoelectrically focused gels that were activity stained with differentially buffered polygalacturonate-agarose overlays revealed that all of the biovar 3 strains produced a single polygalacturonase with a pH optimum of 4.5 and pIs ranging from 4.8 to 5.2. The enzyme was largely extracellular and was produced constitutively in basal medium supplemented with a variety of carbon sources including polygalacturonic acid. Lesions on grape seedling roots inoculated with A. tumefaciens biovar 3 strain CG49 yielded polygalacturonase activity with a pI similar to that of the enzyme produced by the bacterium in culture. These observations support the hypothesis that the polygalacturonase produced by A. tumefaciens biovar 3 has a role in grape root decay.