Title: A new detached-leaf assay to test the inoculativity of psyllids with Candidatus Liberibacter asiaticus associated with huanglongbing disease Authors
Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 20, 2011
Publication Date: June 1, 2011
Citation: Ammar, E., Walter, A.J., Hall, D.G. 2011. A new detached-leaf assay to test the inoculativity of psyllids with Candidatus Liberibacter asiaticus associated with huanglongbing disease. Phytopathology. 101:S6. Technical Abstract: To test the inoculativity of the Asian citrus psyllid (ACP) with Candidatus Liberibacter asiaticus (Las), associated with the Huanglongbing (HLB) or citrus greening disease, psyllids are usually fed singly or in small groups on citrus seedlings and these assayed by polymerase chain reaction (PCR) 3-12 months later. Here, we developed a new ‘detached-leaf assay’ method in which HLB-infected ACP adults were fed for 1 week on detached healthy sweet orange leaves placed in 50-ml polypropylene tubes. One week later, these leaves were processed for quantitative PCR using two Las primers (Li and LJ900). When feeding 10, 5 or 1 ACP/ leaf/week the percentages of Las-positive leaves were 40, 18.8 and 4.4 percent, respectively, using Li primers, and 60, 40.6 and 11.1 percent, respectively, using LJ900 primers. Ct values for Q-PCR using LJ900 primers were much lower than those using Li primers. Our results, using the more conventional but less sensitive Li primers, are largely comparable to those obtained by previous workers using whole citrus seedlings for Las-inoculation by ACP. However, using more sensitive primers can increase the usefulness of this method. We suggest that this new detached-leaf assay method can potentially speed up Las-inoculativity tests on ACP from 3-12 months to only 2-3 weeks, which can greatly enhance pathogen-vector relation studies on Las and ACP.