Genetic studies on ‘Candidatus Liberibacter solanacearum’
Studies have been conducted to determine whether there is any geographic pattern in the known genetic variability of ‘Candidatus Liberibacter solanacearum’. This bacterium is associated with potato zebra chip disease (EPPO A1 List) transmitted by Bactericera cockerelli (EPPO A1 List) in the Americas and New Zealand, as well as with diseases of carrot and celery (Apiaceae) in Europe transmitted by other psyllids (Bactericera trigonica, Trioza apicalis). Comparisons were carried out on a large number of sequences obtained from different geographical sources (Guatemala, Honduras, Mexico, New Zealand, USA, and Finland), as well as from different hosts: Solanaceae (Capsicum annuum, Lycium berlandieri, Solanum betaceum, S. lycopersicum, S. tuberosum), Apiaceae (Daucus carota) and the psyllid vector (Bactericera cockerelli). These comparisons revealed 3 different patterns which could be interpreted as 3 different haplotypes (haplotypes were described by SNPs (single-nucleotide polymorphisms) on the 16S rRNA, 16S/23S intergenic spacer region, 50S rplJ and rpIL ribosomal protein genes). Haplotype ‘a’ was found primarily from Honduras, Guatemala, through Western Mexico to Arizona and California and in New Zealand. Haplotype ‘b’ was found from Eastern Mexico and northwards through Texas to South Central Washington. Haplotypes ‘a’ and ‘b’ corresponded to sequences obtained from solanaceous host plants and B. cockerelli. Their distributions presented some overlap in Texas, Kansas and Nebraska. Haplotype ‘c’ corresponded to sequences obtained from carrot crops in Finland. The authors concluded that these apparently stable haplotypes suggest a long divergence and separation of bacterial populations. They also noted that more studies are needed to verify whether these sequence differences correspond to biological differences in the plant or insect hosts.
Sources
Nelson WR, Fisher TW, Munyaneza (2011) Haplotypes of 'Candidatus Liberibacter solanacearum' suggest long-standing separation. European Journal of Plant Pathology 130(1), 5-12.