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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT Title: Wind speed effects on the quantity of Xanthomonas citri subsp. citri dispersed downwind from canopies of grapefruit trees infected with citrus canker

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

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 2010
Publication Date: June 1, 2010
Citation: Bock, C.H., Graham, J.H., Gottwald, T.R., Cook, A.Z., Parker, P.E. 2010. Wind speed effects on the quantity of Xanthomonas citri subsp. citri dispersed downwind from canopies of grapefruit trees infected with citrus canker. Plant Disease. 94:725-736.

Interpretive Summary: Citrus canker continues to spread in Florida. Storms spread the disease, but little information exists on the interaction of fundamental physical and biological processes involved in its dispersal. Wind/rain events were simulated using a fan to generate wind up to 19 m's-1, and spray nozzles to simulate rain. Greater wind speeds consistently dispersed more canker bacteria measured by concentration or number sampled. Up to 41-fold more were collected at higher wind speeds. The resulting relationship between wind speed up to 19 m/sec and concentration of bacteria collected was linear. Likewise, the number sampled had a linear relationship with wind speed. The quantity of bacteria collected declined with distance, and the relationship was described by an inverse power model. At higher wind speeds more bacteria were dispersed to all distances. Wind borne inoculum in splash in Florida is likely to be important for dispersing large quantities of canker bacteria from infected citrus trees. Disease and crop management aimed at reducing sources of inoculum and wind speeds in a grove should help minimize disease spread by wind-borne inoculum.

Technical Abstract: The epidemic of citrus canker (Xanthomonas citri subsp. citri, Xcc) in Florida continues to expand since termination of the eradication program in 2006. Storms are known to be associated with disease spread, but little information exists on the interaction of fundamental physical and biological processes involved in dispersal of this bacterium. To investigate the role of wind speed in dispersal, wind/rain events were simulated using a fan to generate wind up to 19 m's-1, and spray nozzles to simulate rain. Funnels at ground level and panels at 1.3 m height and distances up to 5 m downwind collected wind-driven splash. Greater wind speeds consistently dispersed more bacteria measured by concentration [colony forming units (CFU) ml-1] or number sampled [bacteria flux density (BFD) = bacteria cm-2 minute-1], from the canopy in the splash. The CFU ml-1 of Xcc collected by panels 1 m downwind at the highest wind speed was up to 41-fold greater than that collected at the lowest wind speed. BFD at the highest wind speed was up to 884-fold higher than that collected at the lowest wind speed. Both panels at distances >1 m and funnels at distances >0 m collected many-fold more Xcc at higher wind speeds compared to no wind (up to 1.4 x 103-fold greater CFU ml-1 and 1.8 x 105-fold the BFD). The resulting relationship between wind speed up to 19 m's-1 and the mean CFU ml-1 collected by panel collectors downwind was linear and highly significant. Likewise, the mean CFU ml-1 collected from the funnel collectors had a linear relationship with wind speed. The relationship between wind speed and BFD collected by panels was generally similar to that described for CFU ml-1 of Xcc collected. However, BFD collected by funnels was too inconsistent to determine a meaningful relationship with increasing wind speed. The quantity of bacteria collected by panels declined with distance, and the relationship was described by an inverse power model (R2 = 0.94-1.00). At higher wind speeds more bacteria were dispersed to all distances. Wind borne inoculum in splash in subtropical wet environments is likely to be epidemiologically significant as both rain intensity and high wind speed can interact to provide conditions conducive for dispersing large quantities of bacteria from canker-infected citrus trees. Disease and crop management aimed at reducing sources of inoculum and wind speeds in a grove should help minimize disease spread by wind-borne inoculum.

Last Modified: 12/17/2014
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