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.
This project is related to Objective 3 of the 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 shell life.
We have tested more than 100 natural compounds (essential oils) for activity against Xanthomonas citri supsp. citri (Xcc). Four of these compounds have been found to be active against Xcc. Screening tests have all been done in vitro in petri plates with pure cultures of the organism. When these active compounds were combined with commercial post harvest waxes on fruit for antimicrobial protection in storage and shipping, there was little antimicrobial protection as the waxes functioned to capture the essential oils and render them inactive. Assessment and testing for other places on the packingline where the antimicrobials could be administrated were not completed due to the problems of Huanglongbing (HLB) in the Florida Citrus Industry and the change in industry priorities.