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United States Department of Agriculture

Agricultural Research Service

Title: The decline in quantity of bacteria of Xanthomonas axonopodis pv citri dispersed from canker-infected citrus plants during wind/rain events

Authors
item Bock, C. H. - UNIV. OF FLORIDA/USDA
item Parker, P. E. - USDA-APHIS
item Cook, A. Z. - USDA-APHIS
item Gottwald, Timothy

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2006
Publication Date: June 1, 2006
Citation: Bock, C., Parker, P., Cook, A., Gottwald, T.R. 2006. The decline in quantity of bacteria of Xanthomonas axonopodis pv citri dispersed from canker-infected citrus plants during wind/rain events. Phytopathology. 96(6): Supplement S13.

Technical Abstract: Background and objectives. Citrus canker (caused by Xanthomonas axonopodis pv. citri, Xac) is an important disease of citrus in several tropical and sub-tropical citrus growing regions. Canker damaged trees produce less yield and the blemished fruit is unfit for fresh sale, so processing becomes the only option. In several afflicted areas the pathogen is under strict eradication, including in Florida. All trees deemed to have been exposed to inoculum (within 1900 ft of an infected tree) are removed (2). However, little is known about the effect of wind on the biological and physical processes of dispersal and infection of Xac (1). The objective of this study was to investigate characteristics of dispersal of Xac bacteria downwind from canker infected plants. Materials and Methods. The effect of wind speed and the characteristics of the downwind dispersal plume of bacteria in wind-blown splash were examined. Wind was simulated using a fan, and spray was generated using a grid of overhead sprayer nozzles above canker-infected plants. Panel and funnel samplers were used to collect the rain splash, and rainfall and wind speed were monitored (3). The bacteria counts were related to wind speeds using regression analysis and ANOVA. Results and Discussion. Greater total quantities of bacteria were collected downwind from infected plants at higher wind speeds. In one experiment the number of bacteria collected by panel samplers at 2 m from the inoculum source was 15833 at 5 ms-1 wind speed and 36758 at 18 ms-1. The total number of Xac bacteria sampled with no wind was 31638, and at 18 ms-1 was 138080, illustrating how wind enhances the dispersal of Xac in rains splash from the foliage of a citrus canopy. The plume of dispersed canker downwind in this simulated system showed that as wind speed increased the plume of bacteria was dispersed further and greater quantities of bacteria were dispersed at greater heights. Higher wind speeds increased the quantity of Xac bacteria dispersed in rain splash away from infected trees. Storm events with high winds are a common occurrence in Florida and could result in enhanced dispersal of Xac bacteria from infected plants. We are currently extending the scope of these studies in natural wind/rain events and in a wind tunnel/rain generating facility at the USDA.

Last Modified: 12/24/2014
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