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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT

Location: Fruit and Nut Research

Title: Effect of the duration of inoculum exposure on development of citrus canker symptoms on seedlings of Swingle citrumelo

Authors
item Bock, Clive
item Graham, Jim -
item Gottwald, Timothy
item Cook, Amanda -
item Parker, Parker -

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 5, 2012
Publication Date: January 29, 2014
Citation: Bock, C.H., Graham, J.H., Gottwald, T.R., Cook, A.Z., Parker, P.P. 2014. Effect of the duration of inoculum exposure on development of citrus canker symptoms on seedlings of Swingle citrumelo. European Journal of Plant Pathology. 138:237-245.

Interpretive Summary: Citrus canker, caused by the plant pathogenic bacterium Xanthomonas citri subsp. citri, Xcc, is a serious disease of citrus in Florida. Canker causes yield loss and cankered fruit are subject to trade restrictions. Cultural management techniques such as windbreaks may work by not only reducing wind speed, but also reducing the period of exposure of susceptible foliage or fruit to those wind speeds that support infection from incoming inoculum. To investigate the effect of exposure period to inoculum of Xcc, seedlings of canker-susceptible Swingle citrumelo were exposed to sprayed inoculum for increasing periods at different wind speeds. The incidence and severity of citrus canker most often increased with longer periods of exposure to inoculum, especially so at wind speeds of =16 m/sec. There was a linear relationship between period of exposure to inoculum and incidence and severity of citrus canker. These results support attempts to minimize exposure of canker-susceptible citrus when wind speed is highest and inoculum is available, and thus windbreaks may help minimize periods of exposure to splashed inoculum in high winds.

Technical Abstract: Citrus canker (Xanthomonas citri subsp. citri, Xcc) is one of the most serious diseases citrus in Florida, and elsewhere in the world. The disease causes yield loss and some fresh fruit trade restrictions may apply. Cultural management techniques such as windbreaks may work by not only reducing wind speed, but also reducing the period of exposure of susceptible foliage or fruit to those wind speeds that support infection from incoming inoculum. To investigate the effect of exposure period to inoculum of Xcc, seedlings of canker-susceptible Swingle citrumelo were exposed to sprayed inoculum for increasing periods at different wind speeds. The incidence and severity of citrus canker was assessed. In three experiments the incidence and severity of citrus canker most often increased with longer periods of exposure to inoculum, especially so at wind speeds of =16 m/sec compared to wind speeds of =5 m/sec (wind speed also increased disease incidence and severity). Regression analysis demonstrated relationships between period of exposure to inoculum and the percent infected leaves per plant, the number of lesions per plant, the number of lesions per infected leaf, and for the percent of infected leaves with lesions on the petioles at wind speeds of =16 m/sec (R2 = 0.16-0.72). Due to the effect of inoculum exposure period and wind speed, attempts should be made to minimize exposure of canker-susceptible citrus when wind speed is highest and inoculum is available, and windbreaks may help minimize periods of exposure to splashed inoculum in high winds.

Last Modified: 10/1/2014
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