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United States Department of Agriculture

Agricultural Research Service

Title: Wind Speed Effects on the Dispersal of Xanthomonas Axonopodis Pv Citri and Infection of Grapefruit Leaves

Authors
item Bock, Clive - UNIVERSITY OF FLORIDA
item Parker, Paul - USDA-APHIS
item Cook, A. Z. - USDA-APHIS
item Gottwald, Timothy

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: September 30, 2005
Publication Date: November 7, 2005
Citation: Bock, C., Parker, P., Cook, A., Gottwald, T.R. 2005. Wind speed effects on the dispersal of xanthomonas axonopodis pv citri and infection of grapefruit leaves. Second International Citrus Canker and Huanglongbing Workshop,Orlando, FL, November 7-11, 2005. C4, p.14.

Interpretive Summary: Citrus canker (caused by Xanthomonas axonopodis pv. citri, Xac) is an important disease limiting yield and marketability of citrus in several tropical and sub-tropical regions. In several afflicted areas, including in Florida, canker eradication has been instigated. The objective of this study was to investigate how wind affects the processes of Xac dispersal and citrus infection. The concentration of bacteria collected under trees did not change at different wind speeds and was consistently greater than that collected 1 m down wind at all wind speeds, but the concentration (and total number) of bacteria collected 1 m down wind had a linear relationship with wind speed. The plume of dispersed canker downwind showed that as wind speed increased the plume of bacteria was dispersed further. Greater quantities of Xac bacteria were also dispersed at greater heights. Higher wind speed also increased infection. The incidence (% leaves) and severity (lesions/plant) of infection was increased, with incidence two times greater at 15 m/sec (~35 mph) compared to no wind. Storm events with high winds are a common occurrence in Florida and not only increase dispersal of Xac bacteria, but also cause greater rates of infection. We are currently extending the scope of these studies in natural wind/rain events and in a wind tunnel/rain generating facility at the USDA.

Technical Abstract: Citrus canker (caused by Xanthomonas axonopodis pv. citri, Xac) is an important disease limiting yield and marketability of citrus in several tropical and sub-tropical regions. In several afflicted areas, including in Florida (1), canker eradication has been instigated. The objective of this study was to investigate how wind affects the processes of Xac dispersal and citrus infection. Wind speeds (0 to 18 m/sec) were simulated using a fan, and spray was generated using overhead sprayers above canker-infected plants (2). For dispersal studies, panel and funnel samplers collected rain splash down wind and under plants, respectively. For infection studies, grapefruit seedlings were sprayed with Xac inoculum (4.7x105 bacteria/ml) at 0, 4, 7 and 15 m/sec wind speeds. Volume collected, bacteria colony counts, and incidence and severity of infection were related to wind speed using regression analysis and general linear modeling. The concentration of bacteria collected under trees did not change significantly at different wind speeds (P=0.05), and was consistently greater than that collected 1 m down wind at all wind speeds. However, the concentration (and total number) of bacteria collected 1 m down wind had a linear relationship with wind speed. In one experiment the total number of Xac bacteria sampled at canopy height 1 m down wind with no wind was 236, and at 18 ms-1 (~40 mph) was 2.8x106, illustrating how wind increases dispersal of Xac in splash from a citrus canopy. The plume of dispersed canker downwind showed that as wind speed increased the plume of bacteria was dispersed further (Figure 1), despite a steep gradient in wind speed with distance from the fan. Greater quantities of Xac bacteria were also dispersed at greater heights. Higher wind speed also increased infection. The incidence (% leaves) and severity (lesions/plant) of infection was increased (Figure 2), with incidence two times greater at 15 m/sec (~35 mph) compared to no wind. Storm events with high winds are a common occurrence in Florida and not only increase dispersal of Xac bacteria, but also cause greater rates of infection. We are currently extending the scope of these studies in natural wind/rain events and in a wind tunnel/rain generating facility at the USDA.

Last Modified: 9/10/2014
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