All authors except RKJ have read and approved the final manuscript.”
“Background Huanglongbing (HLB) is a destructive disease of citrus production worldwide. All known commercial citrus cultivars are susceptible to HLB. The disease was first selleck compound noted in Chaoshan area in Guangdong Province of the People’s
Republic of China in the late of 1800s [1] and is currently distributed in 10 citrus producing provinces in South China. HLB is now established in Sao Paulo of Brazil [2] and Florida of the United States [3] where it poses a great threat to the citrus industry. The disease is associated with three species of non-culturable, phloem-limited, α-Proteobacteria: ‘Candidatus Liberibacter asiaticus’, ‘Ca. L. africanus’, and ‘Ca. L. americanus’ [4, Selleck Smoothened Agonist 5]. In both China and U.S., only ‘Ca. L. asiaticus’ has been detected. Due to the lack of pure culture, ‘Ca. L. asiaticus’ has been poorly characterized. Little is known about the bacterial biology, genetic diversity, and epidemiology. Sequence analyses of conserve genomic loci such as 16S rRNA gene and 16S/23S intergenic spacer regions have been used
to define ‘Ca. Liberibacter’ species [4, 6]. However, more variable genomic loci need to be identified to better characterize the bacterium. Before the availability of whole genome sequence, Bastianel et al. [7] identified an outer member protein gene (omp) to differentiate isolates/strains of ‘Ca. L. asiaticus’ from different geographical origins, although each regions was represented by only one to three strains. Tomimura et al. [8] analyzed the single nucleotide polymorphisms (SNPs) in a bacteriophage-type DNA polymerase gene and revealed three clusters of
‘Ca. L. asiaticus’ strains from the Southeast Asia. All Indonesia strains clustered in one group and the other two clusters were not correlated with geographical origins including Vietnam, Thailand, Taiwan, and Japan. The completed genome sequence of ‘Ca. L. asiaticus’ Strain Psy 62 is now available [9]. The annotated genome has 1,109 protein and 53 RNA coding loci and is readily accessible for genomic analyses. Based on the variation of tandem repeat number (TRN) at the locus of CLIBASIA_01645, the population of ‘Ca. (-)-p-Bromotetramisole Oxalate L. asiaticus’ strains in Guangdong of China was found to differ from that in Florida of U.S. [10]. This analysis of TRN also detected the possible presence of two genotypes in Florida: a TRN < 10 genotype that widely distributed statewide and a TRN > 10 genotype that was limited to central Florida. In Guangdong, TRN variations were more heterogeneous and correlations to geographical origins were not established. A recent report used four tandem repeat loci to analyze ‘Ca. L. asiaticus’ strains from Japan, Taiwan and Indonesia revealed various levels of population diversity, yet correlation to other genotypes or geographical origins was not known [11]. More recently, a prophage terminase gene (CLIBASIA_05610) was used to evaluate population diversity of ‘Ca. L.