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.
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.
Preharvest and postharvest measures were combined to insure that citrus fruit from Florida would not contain citrus canker lesions or any of the citrus canker bacteria. Preharvest sprays combining a carnauba wax with copper hydroxide and other compounds were applied in the groves and reduced the numbers of lesions on the fruit and leaves. The reduction of lesions reduced the number of bacteria available for new infections. When fruit were harvested, there were fewer lesions and less inoculum on or near the fruit. Postharvest measures included introducing sanitizers that were proven to reduce the numbers of bacteria and fungi on the surface of the fruit. Peroxyacetic acid was approved as a canker disinfectant by the Animal and Plant Health Inspection Service (APHIS) after data from this project showed its efficacy to do so. Studies with biological control agents showed that application of some of these organisms could decrease the bacterial survival on the leaves and fruit of the citrus trees. This information could be used as both a pre or post harvest measure to control the occurrence of the bacteria and would be especially useful to the organic growers, as many of these biological control agents are rated for organic farming. Final reports were written and filed as this project concluded.