Submitted to: Florida Scientist
Publication Type: Abstract Only
Publication Acceptance Date: 2/24/2011
Publication Date: 3/11/2011
Citation: Ammar, E., Shatters, R.G., Hall, D.G. 2011. Localization of the bacterium associated with citrus greening disease in various organs of its insect vector Diaphorina citri (Hemiptera, Psyllidae). [abstract). Florida Scientist. 74(1): 3. Interpretive Summary:
Technical Abstract: Candidatus Liberibacter asiaticus (CLas) bacterium has been strongly implicated as the causative agent of huanglongbing (HLB), or citrus greening, which is currently the most devastating citrus disease in Florida as well as in other areas of South America, Asia and Africa. HLB is transmitted in Florida by the Asian citrus psyllid Diaphorina citri in a persistent manner, but its vector interactions with the psyllid vector, particularly at the organ and cellular levels, are poorly understood. We used fluorescent in situ hybridization (FISH) and quantitative PCR (Q-PCR) for the localization of CLas in D. citri. Several FISH protocols have been tested on hemolymph smears and dissected psyllid organs and on leaf sections from HLB-infected citrus plants as positive controls. CLas was detected in the hemolymph, filter chamber and midgut of D. citri collected from HLB-infected citrus trees, as well as in the phloem of infected citrus leaves, but not in healthy control psyllids or leaves. Additionally, Q-PCR detected CLas in dissected organs of individual D. citri adults collected from HLB-infected citrus trees. The proportion of infected salivary glands (47 percent) was significantly lower than those of the alimentary canal (72 percent) or other body parts (79 percent). The relative titer of CLas, compared to psyllid genomic DNA in each sample, was significantly higher in both the salivary gland and alimentary canal compared to that in the rest of the insect body. These results provide the first molecular confirmation of CLas in the hemolymph, alimentary canal and salivary glands of D. citri. They also strongly suggest that the salivary glands constitute a transmission barrier to CLas in the psyllid vector, and that CLas may replicate or accumulate in both the alimentary canal and salivary glands of D. citri.