Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 25, 2011
Publication Date: October 1, 2012
Citation: Bock, C.H., Cook, A.Z., Parker, P.E., Gottwald, T.R., Graham, J.H. 2012. Short distance dispersal of splashed bacteria of Xanthomonas citri subsp. citri from canker-infected grapefruit tree canopies in turbulent wind. Plant Pathology. 61:829-836. Interpretive Summary: Citrus canker is caused by the plant pathogenic bacterium Xanthomonas citri subsp citri [Xcc]. Infection can result in yield loss and market restrictions. The pathogen is spread in rain splash and wind. The objective of the study was to understand the behavior of the downwind plume of Xcc from canker-affected grapefruit canopies at different wind speeds common during rainstorms in Florida. This information can be used to help manage the disease through effective wind break design. Wind speed up to ~20 m sec-1 was tested. The quantity of bacteria collected across the dispersal plume was somewhat variable, but the lowest number of bacteria was consistently collected at the greatest sample height (a negative exponential function). Furthermore, more bacteria were collecetd at a given height at higher wind speeds (an exponential function). Understanding the characteristics of Xcc dispersal from infected citrus canopies will aide development of wind break strategies to minimize pathogen dispersal and infection events.
Technical Abstract: Citrus canker (Xanthomonas citri subsp citri [Xcc]) can result in yield loss and market restrictions. The pathogen is dispersed in rain splash and spread is promoted by wind. The goal of this study was to gain some insight into the behavior of the downwind plume of Xcc from ~1.5 m-tall canker-affected grapefruit canopies at different wind speeds common during rainstorms in Florida. Wind speed up to 19.9 m sec-1 was tested. In all experiments bacteria flux density (BFD, bacteria cm2 min-2) was quantified at heights 30, 70, 110, 130 and 180 cm above ground, and at four points (17, 51, 85 and 119 cm) across the dispersal plume at each height, 1 m down wind. BFD varied substantially among experiments, but the lowest BFDs were consistently detected at the greatest sample height. The relationship between BFD and sample height was described by a negative exponential function (P=0.0690-0.0002, R2 = 0.49-0.99). BFD was greater at a given height with increase in wind speed, and the relationship between BFD and wind speed was described by an exponential function (P=<0.2371-0.0015, R2 = 0.84>0.99). Kolmogorov-Smirnov tests indicated differences in the cumulative distribution functions of the BFD at different wind speeds and heights, but not at specific heights across the plume. Multiple regression analysis demonstrated predictability of the proportion of total bacteria collected at any point (F=150, P<0.0001, R2= 0.53). Understanding the characteristics of Xcc dispersal from infected citrus canopies will help in development of wind break strategies to minimize pathogen dispersal and infection events.