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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT Title: Predisposition of citrus foliage to infection with Xanthomonas citri subsp. citri

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

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2012
Publication Date: January 1, 2013
Citation: Bock, C.H., Graham, J.H., Cook, A.Z., Parker, P., Gottwald, T.R. 2013. Predisposition of citrus foliage to infection with Xanthomonas citri subsp. citri. Journal of Plant Pathology. 95:99-106.

Interpretive Summary: Citrus canker is caused by Xanthomonas citri subsp. citri, Xcc a plant pathogenic bacterium. It is a serious disease of susceptible citrus in Florida and other citrus-growing areas of the world. Leaf preconditioning as a route for entry of the bacteria is poorly characterized. Experiments were designed to investigate the effects of wind and rain and high humidity and mild abrasion in predisposing citrus foliage to infection with Xcc. Exposure of leaves of citrus seedlings to wind and rain caused significant injury and leaves developed up to two fold as high an incidence and 10-fold as high severity compared to leaves on seedlings of non-treated control plants. The points of attachment of the lamina to the petioles were particularly susceptible to wind-induced injury. There was no effect of humidit on disease incidence or severity compared to the non-treated control. Mild leaf abrasion of grapefruit seedlings with sand increased incidence and severity of disease two-fold. Ways to reduce leaf injury by minimizing wind speed in orchards will contribute to reducing canker incidence and severity

Technical Abstract: Citrus canker (caused by Xanthomonas citri subsp. citri, Xcc) is a serious disease of susceptible citrus in Florida and other citrus-growing areas of the world. The effect of leaf preconditioning as a route for entry of the bacteria is poorly characterized. A series of experiments were designed to investigate the effects of wind and rain (to simulate a storm), high humidity (>90%) and mild abrasion with sand (to simulate wind blow sand and debris) in predisposing citrus foliage to infection with Xcc. Exposure of leaves of Swingle citrumelo seedlings to wind and rain (16 m sec-1 and 235 mm h-1, respectively) for 15 or 30 min caused significant injury and leaves developed up to two fold as high an incidence and 10-fold as high severity compared to leaves on seedlings of non-treated control plants. The points of attachment of the lamina to the petioles were particularly susceptible to wind-induced injury with up to 25% showing symptoms compared to 0% for the non-treated control. Over 80% of injured leaves had lesions associated with the site of injury. There was little or no effect of humidity >90% for 1.5 or 2.5 h on disease incidence or severity compared to the non-treated control. Mild leaf abrasion of grapefruit seedlings with sand increased incidence and severity of disease two-fold. Ways to reduce leaf injury by minimizing wind speed in orchards will contribute to reducing canker incidence and severity.

Last Modified: 11/23/2014
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