ARS | Publication request: Guangdong and Florida Populations of “Candidatus Liberibacter asiaticus” Distinguished by a Genomic Locus With Short Tandem Repeats

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2010
Publication Date: May 13, 2010
Citation: Chen, J., Deng, X., Sun, X., Jones, D., Irey, M., Civerolo, E.L. 2010. Guangdong and Florida Populations of “Candidatus Liberibacter asiaticus” Distinguished by a Genomic Locus With Short Tandem Repeats. Phytopathology. 100:567-572.

Interpretive Summary: Huanglongbing (HLB) is a highly destructive disease that threatens citrus production worldwide. The disease, also referrred to as yellow shoot disease and citrus greening, has been known in Guangdong, P. R. China, for over a hundred years. HLB was found in Florida, USA, in 2005. An unculturable bacterium, named as “Candidatus Liberibacter asiaticus”, has been associated with HLB. It is not clear how the HLB bacteria in Florida are related to HLB bacteria in Guangdong. In this study a unique genomic marker in the HLB bacterium was used to distinguish the HLB bacterial population in Guangdong, from the HLB bacterial population in Florida. Also, two genetically different HLB bacterial strains were found in Florida. One of these was widespread throughout the state and the other was limited to central Florida. This is the first report of the differentiation of “Ca. L. asiaticus” populations from different geographic regions. This information should aid understanding of the epidemiology of HLB around the world and lead to the development of effective disease management strategies.

Technical Abstract: Huanglongbing (HLB, yellow shoot disease) is a highly destructive disease that threatens citrus production worldwide. The disease was first observed in Guangdong, P. R. China over 100 years ago, and was found in Florida, USA in 2005. “Candidatus Liberibacter asiaticus” has been associated with HLB in many citrus-growing regions around the world, including Guangdong and Florida. The relationships of “Ca. L. asiaticus” populations in different geographical regions are of high importance in HLB epidemiology and control. In this study, we identified a genetic marker containing small tandem repeats in the genome of “Ca. L. asiaticus” and comparatively analyzed the tandem repeat numbers (TRNs) in “Ca. L. asiacticus” populations from Guangdong and Florida. Analyses on TRNs showed that the bacterial population in Guangdong was distinct from that in Florida. The Guangdong population was characterized by strains of TRN7 with a frequency of 47.6%. The Florida population was predominated by strains of TRN5 with a frequency of 84.4%. Further analyses grouped the bacterial strains into two genotypes: TRN<10 and TRN>10. TRN<10 strains are widely distributed in all HLB-affected counties in Florida. TRN>10 strains are aggregated in central Florida. This is the first report on differentiation of “Ca. L. asiaticus” populations from different geographical regions and the presence of two differently distributed genotypes of “Ca. L. asiaticus” in Florida.