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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT

Location: Fruit and Nut Research

Title: Infection and decontamination of citrus-canker-inoculated leaf surfaces

Authors
item Bock, Clive
item Graham, Jim -
item Parker, Paul -
item Cook, Amanda -
item Gottwald, Timothy

Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 8, 2010
Publication Date: February 15, 2011
Citation: Bock, C.H., Parker, P. E., Cook, A. Z., Graham, J. H. and Gottwald, T. R. Infection and decontamination of citrus canker-inoculated leaf surfaces. Crop Protection 30: 259-264. 2011.

Interpretive Summary: Citrus canker is spreading to new areas in Florida. Personnel and equipment decontamination is practiced in both disease-endemic and disease-free areas to reduce the risk of bacterial spread by man or machinery. Grapefruit leaf surfaces were used to explore the efficacy of a commonly used personnel sprayer system applying a quaternary amine decontaminant. After treatment, there was a large and rapid decline in the quantity of live bacteria with one pass through the spray hoop (>80% decrease in number of canker bacteria), and multiple sprays (2-6) resulted in up to 100% mortality, although the first spray invariably caused the highest proportion of bacteria. The effect of the decontaminant spray was immediate (within 0.5 minutes only 3-11% of surface bacteria survived, and by 20 minutes <1-3% survived). Based on these results, personnel sprayers with a quaternary amine compound are an effective way to reduce surface contamination. All the inoculated plants developed symptoms of citrus canker, even those receiving six decontaminant sprays indicating that infection occurred at, or very soon after, inoculation, and the canker bacterium was in protected sites inside the leaf before exposure to the decontaminant spray.

Technical Abstract: Citrus canker (Xanthomonas citri subsp. citri, Xcc) is now considered endemic in Florida and continues to spread. Personnel and equipment decontamination is practiced in both disease-endemic and disease-free areas to reduce the risk of bacterial spread by man or machinery. We used grapefruit leaf surfaces to explore the efficacy of a commonly used personnel sprayer system applying a quaternary amine decontaminant. In three experiments, plants in flush (leaves ¾ expanded) were inoculated (~105 CFU ml-1). Immediately after inoculation, plants were passed through the sprayers 0, 1, 2, 3, or 6 times. Leaves were sampled at 0.5, 10 and 20 min after decontamination and tested for viable Xcc by dilution plating. There was a large and rapid decline in the quantity of live bacteria with one pass through the spray hoop (>80% decrease in CFU ml-1), and multiple sprays (2-6) resulted in up to 100% mortality of surface Xcc. Presumably more thorough coverage with multiple sprays killed remnant bacteria, although the first spray invariably caused the highest proportion of population mortality. The effect of the decontaminant spray was immediate (within 0.5 minutes only 3-11% of surface bacteria survived, and by 20 minutes <1-3% survived). Based on these results, use of a personnel sprayer with a quaternary amine compound is highly effective for reducing surface inoculum. A single spray kills a high proportion of the population, but multiple sprays increase mortality of Xcc. All the Xcc-inoculated plants subsequently developed symptoms of citrus canker. No significant difference in incidence or severity of grapefruit leaf infection was detected among decontamination treatments or compared to the untreated control. This finding indicates that infection occurred at, or very soon after, inoculation, and that Xcc was in protected sites inside the leaf before exposure to the decontaminant spray.

Last Modified: 7/25/2014
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