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Title: The effect of wind on dispersal of splash-borne Xanthomonas citri subsp citri at different heights and distances downwind of canker-infected grapefruit trees

Author
item Bock, Clive
item Gottwald, Timothy
item COOK, AMANDA - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center
item PARKER, PAUL - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center
item GRAHAM, JAMES - University Of Florida

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2011
Publication Date: 1/1/2012
Citation: Bock, C.H., Gottwald, T.R., Cook, A.Z., Parker, P.E., Graham, J.H. 2012. The effect of wind on dispersal of splash-borne Xanthomonas citri subsp citri at different heights and distances downwind of canker-infected grapefruit trees. Journal of Plant Pathology. 93:667-677.

Interpretive Summary: Citrus canker is caused by the plant pathogenic bacterium Xanthomonas citri subsp citri (Xcc). Xanthomonas citri subsp citri is a major pathogen of grapefruit and other canker-susceptible citrus species and cultivars grown in Florida and elsewhere. It is dispersed by rain splash, and wind promotes the dispersal of the pathogen. The aim of this study was to explore the relationships between wind speed and the number of bacteria dispersed downwind to different heights at different distances. There was a rapid decline in mean the bacteria flux density (BFD, bacteria/ml/min) of Xcc collected at greater heights and distances downwind at all wind speeds, although higher wind speed resulted in greater dispersal. Disease management aimed at reducing sources of inoculum, and wind speeds to reduce dispersal of inoculum within orchards, is discussed.

Technical Abstract: Xanthomonas citri subsp citri (Xcc), which causes citrus canker, is a major pathogen of grapefruit and other canker-susceptible citrus species and cultivars grown in Florida and elsewhere. It is dispersed by rain splash, and wind promotes the dispersal of the pathogen. The aim of this study was to explore the relationships between wind speed and the number of bacteria dispersed downwind to different heights at different distances. Wind (up to 20 m s-1) was generated using a fan, and rain simulated using sprayer nozzles. Negative exponential models described the relationship between height and the bacteria flux density (BFD, bacteria cm-2 min-1), with a rapid decline in mean the BFD of Xcc collected at greater heights (P = <0.0001-0.3838, R2= 0.56 - 1.00). A power model described the relationship between distance and BFD of Xcc collected at most heights and wind speeds (P=0.049 - <0.0001, R2 = 0.78-1.00). A multiple regression analysis based on wind speed, height and distance suggested predictability of the proportion of the total BFD of Xcc collected downwind of the simulated wind-rain system (F=49, P<0.0001, R2= 0.46). Disease management aimed at reducing sources of inoculum, and wind speeds to reduce dispersal of inoculum within orchards, is discussed.