Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2004
Publication Date: 1/1/2005
Citation: Bock, Clive, Parker, Paul, Gottwald, Tim R. 2004. The Effect of Simulated Wind-Driven Rain on Duration and Distance of Dispersal of Xanthomonas Axonopodis pv citri from Canker Infected Citrus Trees. Plant Disease. 89:71-80. Interpretive Summary: Citrus canker is currently the target of an intensive eradication program in south Florida. The dispersal and deposition of bacteria from infected plants is not well understood, but is information of direct value to the eradication program and for the future management of the disease. The distribution of disease has implicated the combined effects of wind and rain in the spread of canker bacteria within fields and over distances of hundreds of meters. This paper reports the results of a series of experiments that were conducted to investigate the combined effects of simulated wind and rain splash on dispersal of bacteria from infected trees. The results showed that bacteria are dispersed in large quantities during the initial five minutes of the dispersal event, and the quantity of bacteria dispersed rapidly declined thereafter to about one-tenth the initial quantity, a level at which the bacteria can be dispersed for at least several days. Bacteria were readily caught 12 m from canker-infected plants, and this illustrates that they are readily dispersed in wind blown spray from infected plants. The results illustrate how the canker bacteria are adapted to immediate dispersal in wind/rain events and that these spray and splash borne bacteria have the potential to be dispersed substantial distances.
Technical Abstract: Dynamics of dispersal of bacteria of citrus canker (Xanthomonas axonopodis pv citri) were assessed in simulated wind driven rain splash. The wind/rain splash events were simulated using electric blowers to generate wind and sprayer nozzles to produce water droplets. The spray was blown at canker-infected trees 1 m down wind. The duration over which bacteria were dispersed was assessed over 52 h after commencing a rain splash event. Initially large quantities of bacteria were recovered from samples (104 bacteria per ml), but the numbers declined to 103 per ml after 1 h and remained at that level for the duration of the experiment. In a more detailed study of dispersal the greatest numbers of bacteria were dispersed during the first 5-min period (1.34 x 105 bacteria per ml). By ten minutes after initiation of dispersal approximately one-third of the initial number was being dispersed, and by the end of the first hour only one-tenth the initial quantity was dispersed. Funnel samplers placed at ground level under the trees showed a similar trend. The distance to which bacteria were dispersed in wind blown splash was also tested under simulated conditions - bacteria were collected at all distances sampled (up to 12 m), but most were deposited at 1 m (4.2 x 107 bacteria per m2). An inverse power law regression model best described the data on duration and distance of dispersal. Citrus canker is readily dispersed in wind-driven rain and is dispersed in large quantities immediately after the stimulus occurs, upon which wind driven splash can disperse inoculum over a prolonged period and over a substantial distance.