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United States Department of Agriculture

Agricultural Research Service

Research Project: EMERGING DISEASES OF CITRUS, VEGETABLES, AND ORNAMENTALS

Location: Subtropical Plant Pathology Research

Title: Variability of direction of tree-to-tree spread of HLB over time

Authors
item Kriss, Alissa
item Silvio, Lopes -
item Gottwald, Timothy

Submitted to: International Research Conference on Huanglongbing
Publication Type: Abstract Only
Publication Acceptance Date: February 1, 2013
Publication Date: N/A

Technical Abstract: Candidatus Liberibacter americanus and Candidatus Liberibacter asiaticus are two bacterial species that cause huanglongbing (HLB) disease in citrus-growing regions of Brazil. A concentrated sampling plan of a grove in Matao, Brazil was initiated to evaluate the spatial and temporal spread of these bacteria. The exact location of each of 8697 trees was recorded, and each symptomatic tree was assessed by PCR for the presence of Ca. L. americanus and Ca. L. asiaticus during 17 different months from April 2006 to May 2008 (Fig. 1). In the first month, only five trees were confirmed to have Ca. L. asiaticus. The first trees with confirmed cases of Ca. L. americanus were not found until February 2007. By the end of the study, 43 trees were confirmed to have Ca. L. americanus, 1164 trees were confirmed to have Ca. L. asiaticus, and three trees were coinfected. For the new trees each month that were confirmed to have Ca. L. asiaticus, their distance (m) from previously infected trees was calculated. This process continued for each of the 17 months and for all lag times from 3 to 24 months (lag is defined here as the time from visual symptoms on one tree to visual symptoms on a newly infected tree). Directionality of disease spread was then examined. The absolute difference between the direction (North = 0°) from an infected tree to other trees it was determined to possibly infect and the direction from that infected tree to a newly infected tree were found. Results indicate that predictions of tree-to-tree spread should take the direction of previously found infections into account versus assuming that all trees around an infected tree (i.e., a 360° circle around an infected tree with some radius) have equal probability of being infected by psyllids from a symptomatic tree.

Last Modified: 9/23/2014
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