Abstract: Huanglongbing (HLB) , previously known as greening disease, is probably the most serious disease in citrus. The presumptive causal agent is believed to be a non-cultured, phloem-restricted α-proteobacterium. Currently, there are three Candidatus Liberibactor spp. associated with citrus Huanglongbing
(HLB) disease, Ca. Liberibactor asiaticus, Ca. Liberibactor africanus and Ca. L iberibactor am ericanus. In this study, a genomic walkingmethod was used to obtain new sequences extended from previously known loci,
rplKAJL-rpoBC, 16S/23S rRNA and outermembrane protein (omp) of Ca. L iberibactor asia ticus. In rplKA-JL-rpoBC locus, 3 218 bp of new sequenceswere obtained at the 5′up stream end and 2 653 bp at the 3′down2
stream. Totally, fragments about 1 853 bp and 2 459 bp were also acquired from 5′up stream and 3′down-stream of 16S/23S rRNA region, respectively. Similarly, in om p locus, fragment about 4 014 bp were obtained at 5′up stream and 971 bp at 3′downstream, respectively. Genomic walking approach was used in this study, and totally 15 168 bp non2redundancy sequences from asiaticus specieswere obtained. Sequence analysis shows that there are two new genes (suhB and serA) at the rplKAJL-rpoBC gene cluster locus, four new
genes ( transmembrane p rotein gene, cell wall hydrolase pseudogene, 5S ribosomal RNA and tRNA^Met ) extended from the 16S/23S rRNA gene locus and six new genes (rpsB, tsf, pyrH, frr, cdsA2, cds2) at the omp locus. These new sequences obtained in this study will facilitate the PCR2based HLB research.

Key words: citrus, Huanglongbing, Candidatus Liberibactor, sequence