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United States Department of Agriculture

Agricultural Research Service

Research Project: EMERGING DISEASES OF CITRUS, VEGETABLES, AND ORNAMENTALS

Location: Subtropical Plant Pathology Research

Title: Effects of postharvest treatments on recovery of Xanthomonas citrisubsp. citri from infected grapefruit leaves

Authors
item Anco, Dan -
item POOLE, GAVIN
item GOTTWALD, TIMOTHY

Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2014
Publication Date: May 6, 2014
Citation: Anco, D.J., Poole, G.H., Gottwald, T.R. 2014. Effects of postharvest treatments on recovery of Xanthomonas citrisubsp. citri from infected grapefruit leaves. Crop Protection Journal. 62:115-123.

Interpretive Summary: Leaves of ‘Duncan’ grapefruit were inoculated with the citrus canker bacterium and subjected to various treatments of temperature, disinfectant, and duration. In general, recovery of the bacterium decreased with increasing temperature and treatment duration, and decreases were greater in the presence of the disinfectant Pro-San. Tissue damage, when observed, was limited to the youngest, most supple leaves subjected to elevated temperatures for ~10 min duration. Reductions of bacterial titer were in excess of 99% after treatment at 50C for 20 min in the presence of Pro-San. Results may be useful in influencing future regulatory policies regarding trade of citrus foliage, especially those used as condiments.

Technical Abstract: Studies were conducted to evaluate treatments to reduce recovery of Xanthomonas citri subsp. citri (Xcc) in infected grapefruit leaves. To investigate effects of temperature (0, 10, 40, and 50°C), disinfectant (none or Pro-San), and treatment duration (0, 2, 10, and 20 min) on recovery of Xcc in vitro, a split-split plot experimental design was utilized. Recovery of Xcc in vitro in the absence of Pro-San decreased with increasing treatment duration at 50°C but not at temperatures < 50°C. No Xcc recovery in vitro was observed after any treatment combination involving Pro-San. Decontamination of grapefruit leaves infected with Xcc in relation to disinfectant (none or Pro-San), temperature (0, 10, 40, 45, and 50°C), treatment duration (0, 2, 5, 10, and 20 min), and assessment time (0, 2, 7, and 14 days post treatment [dpt]) was examined using a split-split-split plot design. Reductions in Xcc recovery generally increased with increasing treatment duration and temperature, and they were greater for treatments involving Pro-San. To examine the general trend of increased Xcc recovery with increasing dpt, nonlinear mixed regression analysis was used to fit a monomolecular model to relative Xcc recovery data. Results indicated that increases in relative Xcc recovery after 14 dpt were insignificant and unsubstantial. Treatment at 45°C for 20 min or 50°C for > 5 min resulted in leaf tissue damage in some instances; in two cases, tissue damage was observed on control leaves 14 dpt. Experiments were conducted to investigate the relationships of tissue damage with leaf age and tissue damage localization with inoculation location. Tissue damage was observed on only the youngest, most supple leaves, and its localization did not appear to be related to naturally occurring citrus canker lesions or experimental phosphate-buffer-inoculation sites. Results from these studies may be useful in influencing future regulatory policies regarding trade of citrus foliage, especially those used as condiments.

Last Modified: 7/28/2014
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