Novel phytoplasma strains of X-disease group unveil genetic markers that distinguish North American and South American geographic lineages within subgroups 16SrIII-J and 16SrIII-U

摘要

Phytoplasmas in the X-disease group (16SrIII) are highly diverse in terms of geographic distributions, vectorship and plant host specificity. Such biological and ecological diversity is often correlated with distinctive genetic markers present in evolutionarily conserved genes. Based on restriction fragment length polymorphism (RFLP) markers in the 16S rRNA gene sequences, 29 subgroups have been delineated, with most of them being found in the Americas. However, it has been unknown whether distinct geographic lineages are present within a given subgroup. Prior to this study, phytoplasmas belonging to subgroups 16SrIII-J and 16SrIII-U were reported only in countries located in South America. In the present study, we identified new phytoplasmas strains closely related to the reference strains of the two subgroups in Mexico, a North American country. These newly identified Mexican strains possess unique RFLP, single nucleotide polymorphism, and fragmental deletion markers in 16S rRNA- and/or ribosomal protein-encoding genes. Since these markers consistently distinguished the Mexican strains from their South American counterparts, they may represent emerging or previously unknown North American geographic lineages of the subgroups 16SrIII-J and 16SrIII-U.