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 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.
Providing verification that fresh Florida citrus leaving packinghouses is completely devoid of viable canker bacterial cells (Xanthomonas citri subsp. citri, Xcc) remains a problem for packers. An integrated approach has been developed by the ARS which consists of both pre and post harvest measures. Preharvest methods include spraying with compatible prophylactics which are carried in an ARS (USHRL, CSPRU) patented (WashGard®) formulation which resists erosion of the pesticide by ultra violet (UV) light, wind and rain and maintains both the concentration and the activity of the compound. Post harvest measures include sanitation with a canker approved sanitizer (peroxyacetic acid 85-100 ppm) shown by ARS scientists to eradicate bacterial cells on the peel surface. For cells that may be imbedded in the peel and are not often reached by sanitizers, antimicrobial compound(s) carried in a commercial wax would provide prolonged protection against any remaining viable cells. We are studying compatibility of commercial waxes with several natural antimicrobial compounds that are active against Xcc. Modified atmosphere is also being researched, with varying concentrations of oxygen, carbon dioxide and nitrogen in citrus storage areas to destroy pathogens in or on the fruit. We have shown these modified atmosphere studies can reduce viable cells in small cankers. This study is ongoing.