1a. Objectives (from AD-416):
Develop a fruit treatment method to help lift the quarantine that prohibits the shipment of citrus fruit from Florida to many areas, which is devastating the citrus industry. Our work is directed towards developing a system of sanitizers and antimicrobials applied on the packingline which would insure that there were no living Xanthomonas citri subsp. citri (Xcc) cells in fruit leaving the packinghouses. Also we will be looking at the various lesion types to help explain the lack of infection from old lesions and virulence of many leaf lesions.
1b. Approach (from AD-416):
Initially we will be screening experimental compounds in the laboratory by in vitro testing with petri- dishes and pathogens of citrus to see if there is an indication of success with these compounds. This would involve using protocols already in place in addition to utilizing new methods for testing. Concurrently we will be testing packingline protocols already in place to see how much, if any, antimicrobial capabilities are already on the line. The compounds that are active against Xanthomonas citri subsp. citri (Xcc) will be tested on a pilot packingline at the Winter Haven facility. If these compounds are successful on this line, the protocol will be scaled up for trial in a commercial packinghouse. In the field we will be collecting fruit, twig and leaf lesions for the infection study. The lesions will be tested for biofilm development using fluorescent microscopy and changes in the microbial communities in the lesions will be evaluated by various isolation techniques and organisms identified by molecular protocols.
3. Progress Report:
This project is related to Objective 3 of this in-house project: Develop pre- and postharvest treatment protocols for reducing specific decay pathogens using sanitizers, antimicrobials, such as plant (including citrus) essential oils, with or without coatings and/or other surface treatments and storage atmospheres to minimize postharvest losses and maximize shelf life. Novel postharvest sanitation measures are being evaluated to destroy bacteria on fruit surfaces to eliminate the threat of viable bacteria and open international markets. Development of antimicrobial coatings is continuing, assessing compatibility of active natural antimicrobials with commercial postharvest waxes. Studies on the ecology of the canker lesion continue and recent data show that when the bacterium is ‘stressed’ by treatments (e.g. high heat or exposure to antimicrobials) the colony changes and a companion cell becomes the dominant cell form rather than the canker bacterium. Depending on the treatment there are various ratios of the two cell types which may play a role in the success of the canker bacterium as an epiphyte and its virulence as a pathogen. Data also show that these bacteria may be able to process toxic compounds in such a way that the bacterial cells are eventually able to overcome the toxicity and begin to grow. Biological control studies in the greenhouse have been suspended temporarily because of the move from Winter Haven to Ft. Pierce and the lack of available greenhouse facilities.