Submitted to: Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/26/2011
Publication Date: 11/8/2011
Citation: Bock, Clive H., Gottwald, Timothy R. 2011. Processes involved in the dispersal of Xanthomonas citri pv. citri from canker-infectd citrus canopies, and in the infection of citrus foliage. In: Proceedings of the Workshop on Xanthomonas citri/Citrus canker, November 17-18, 2011, Ribeirao Preto, Brazil. p. 27-30.
Technical Abstract: Citrus canker (Xanthomonas citri subsp. citri, Xcc) is now considered endemic in Florida, and epidemics result in yield loss and market penalties both in Florida, and elsewhere where the pathogen occurs, and susceptible citrus is cultivated. The bacterium is dispersed in rain splash, and storms with strong winds and heavy rain are common in Florida. Understanding the interaction of the physical (wind and splash) and biological (bacteria production, dispersal and infection) factors involved can help guide development of effective management strategies, such as the use of wind breaks. In a series of experiments simulating wind and rain the dynamics of these processes were investigated. Bacteria were produced and dispersed in splash continuously for up to 52 h (the maximum time tested), although numbers declined rapidly during the first 10 minutes of a dispersal event. Higher wind speeds result in greater quantities of bacteria escaping the canopy downwind in wind driven splash, the relationship being exponential with respect to wind speed (R2 = 0.84>0.99). With wind, Xcc was dispersed further down wind, and bacteria were collected up to 12 m downwind of an infected canopy (the maximum distance tested) where the canopy was subject to a wind speed of ~20 ms-1. However, the quantity of bacteria dispersed declined with distance. The relationship was described by an inverse power function (R2 = 0.94-1.00), and at higher wind speeds more bacteria were dispersed to all distances. Furthermore, there is a gradient of Xcc across the vertical plane of the downwind dispersal plume – with a negative exponential function describing the relationship between height and bacteria collected (R2 = 0.49-0.99). Regarding infection of citrus, wind speeds (>10 m sec-1) consistently resulted in higher incidence and severity of citrus canker developing, with a dramatic increase in disease between 10 and 15 ms-1. Injury to leaves due to wind was evident at wind speeds =13 m sec-1. The relationship between wind speed and disease, and wind speed and injury was described by a logistic model (R2 = 0.61-1.00). More disease was associated with visible injury as the wind speed increased, and disease not associated with visible injury also increased with wind speed. The availability of Xcc inoculum affected disease incidence and severity, with greater concentrations resulting in more disease. These results demonstrate the role of wind and splash in dispersal of Xcc and facilitating infection of susceptible citrus. Reducing wind speed in citrus groves with the aid of wind breaks should contribute to a reduction in the severity of an epidemic by reducing dispersal and infection events.