Huanglongbing (HLB) is considered as one of the most destructive and devastating disease of citrus trees worldwide. In the present study, we analyzed the genetic diversity of the 16S rDNA gene sequence of ‘Candidatus Liberibacter asiaticus’ (‘Ca.L. asiaticus’) strains from symptomatic trees of Citrus latifolia and Citrus aurantifolia with HLB and performed comparative analysis with sequences in the GenBank database. Two hundred and fourteen (214) samples of trees collected in the Yucatán Peninsula were analyzed using PCR amplification and real-timeq PCR. We detected twenty-five positive trees by PCR, although the positive trees were increased to seventy by real-time q PCR. Blast searches of 75 sequences of 1167 bp in size obtained by PCR-positive trees revealed 99 to 100% similarity with sequences of ‘Ca.L. asiaticus’. Multiple alignment showed 2 clusters of sequences, wherein the first group were 100% identical, and the second group was characterized by the presence of polymorphic sites distributed across the gene sequence. The consensus sequence of the first group was named H36PENINSULAR. Analysis of the 16S rDNA sequences from GenBank revealed the same behavior, wherein one group exhibited 100% similarity (within the group). Alignment of the first groups from each of the two analyses above revealed a complete match between them (100% similarity). Accordingly, we suggest that sequence H36PENINSULAR be considered the principal haplotype of the 16S rRNA gene of ‘Ca.L. asiaticus’ because it exhibits worldwide distribution and dominance.
Key words: Huanglongbing, 16s rRNA gene, ‘Candidatus Liberibacter asiaticus’, Mexican lime, Persian lime.