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. This research was undertaken to help remove the quarantine from the Florida fresh citrus industry due to citrus canker disease (Xcc). Infection lesion ecology is poorly understood and some knowledge of the lesion and the communities of organisms living within are necessary to be able to control the spread of disease and measure the parameters that determine virulence. If certain stages of the lesion contain cells that are not virulent, an avenue is open to reduce inoculum when the cells are least aggressive, bringing fewer viable cells into the packinghouse. The reduction of cells coming onto the packing line on citrus fruit would mean that the challenge of eliminating high numbers of aggressive organisms by protocols on the line is not as great. We have isolated organisms from various age and stage lesions and are looking at their occurrence and identification in the laboratory. Cooperators are looking at virulence of lesions in the field. Antimicrobial compounds and sanitizers effective against Xcc are being studied as part of this protocol. Preliminary data for this study show that our preharvest experimental sprays were able to significantly reduce canker in the field as well as melanose, another disease that can limit fruit sales for the fresh market. This technology may also prove useful towards blackspot, a new disease threat to Florida citrus. Greenhouse studies with grapefruit seedlings have begun in order to test activity of several biological control agents against Xcc. This is an ongoing study. Progress was monitored by e-mail, phone calls and meetings.