1a. Objectives (from AD-416)
To establish methods to ascertain that asymptomatic fruit leaving the packinghouse for market will be free of viable cells of the bacterium that causes citrus canker (Xanthomonas axonopodis pv citri). These methods will insure that bacteria established in small wounds and abrasions will not be able to cause disease when transferred to different localities.
1b. Approach (from AD-416)
Studies will be undertaken using wounded inoculated fruit to better understand the capabilities of the pathogen to survive certain sanitation and treatment protocols. Should the pathogen survive packingline sanitation in wounds, a further antimicrobial treatment would insure no viable cells leave the packinghouse. Compounds will be screened using novel methods for their abilities to reduce or eliminate growth of Xanthomonas. These will be done on a continuing basis: antimicrobial compounds will be screened and compatible coatings found that will act as a carrier for them. These measures will be combined with sanitizers to form a system that will be consistently effective in reducing the occurrence of viable bacterial cells in the ready-to-ship product. The most efficient method in the laboratory setting will be scaled up to packinglines and tested for efficiency on inoculated and un-inoculated asymptomatic injured and non-injured fruit.
3. Progress Report
This project is related to Objective 2 of this in-house project: Relate chemical composition to sensory flavor and pathogen resistance data from Objective 1 to determine which compounds are important for flavor or have antimicrobial properties. Florida’s fresh citrus industry had been hurt by a quarantine prohibiting the shipment of citrus fruit to any citrus producing states. For states where minimal shipping is allowed, there is a costly set of rules that packers must obey to be in compliance to ship. The restriction for shipping is the result of living bacterial cells of the canker organism (Xcc) found on fruit that had been processed through a packingline. The possibility remains, however small, those bacterial cells will be carried on the fruit and escape, causing outbreaks of this disease in places where it has not yet reached. This study involves testing compounds that will eliminate any bacteria still viable in wounds or biofilms on the surface of the fruit. Compounds that have been tested are essential oils and by-products from citrus and other natural sources. Our preliminary data shows that some essential oils are active against this bacterium. We are experimenting with vehicles to carry these antimicrobial compounds onto the fruit and make them compatible with the packingline. Application of these antimicrobials to the fruit will insure that there are no viable bacterial cells leaving the packinghouse. This research has resulted in a publication on a new method to screen antimicrobials. New studies have shown that chlorine dioxide can destroy Xcc cells when growing under laboratory conditions. We are collecting new and aggressive lesions and bacteria from the field this year and subjecting them to various concentrations of chlorine dioxide with active natural volatiles to see if there would be synergetic effect. This is an ongoing study.