ARS | Publication request: Population diversity of ‘Candidatus Liberibacter asiaticus’ in southern China revealed by tandem repeat number variation in a hypervariable genomic locus

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 14, 2012
Publication Date: August 4, 2012
Citation: Ma, W., Wen, X., Gu, Y., Deng, X., Chen, J. 2012. Population diversity of ‘Candidatus Liberibacter asiaticus’ in southern China revealed by tandem repeat number variation in a hypervariable genomic locus. Phytopathology. 102:S4.74.

Technical Abstract: ‘Candidatus Liberibacter asiaticus’ is a putative pathogen of citrus Huanglongbing (HLB, yellow shoot disease). HLB is highly destructive and has occurred in southern China for over a hundred years. Due to unsuccessful in vitro cultivation of the bacterium and lack of efficient markers to discriminate bacterial strains, population diversity of ‘Ca. L. asiaticus’ in southern China remains poorly studied. A PCR primer set flanking a genomic region with variable tandem repeat numbers (TRNs) has been developed to differentiate ‘Ca. L. asiaticus’ populations in Guangdong, China and Florida, U.S.A. (Phytopathology 100:567-572). In this study, TRN variations of ‘Ca. L. asiaticus’ were further investigated with samples from Guangdong and seven other provinces (Fujian, Guangxi, Guizhou, Hainan, Jiangxi, Yunnan, and Zhejiang) in southern China. Among the 226 HLB samples analyzed, 177 (78.3%) yielded single PCR amplicons. Sequence analysis showed a continuous distribution of TRNs ranging from 2 to 24 among the 177 amplicons, with the mode at TRN=8 (39 samples, 22.0%). The wide TRN range suggests a high level of bacterial population diversity that matches well with the long history of HLB in China. On the other hand, over 60% of the samples had TRNs of 6, 7 or 8, suggesting selection of these genotypes. Interestingly, 49 out of the 226 (21.7%) samples showed multiple PCR amplicons. Results from sequence analyses suggested the presence of multiple genotypes/strains of ‘Ca. L. asiaticus’ in a single citrus host.