Diversity of the ‘Candidatus Phytoplasma asteris’ and ‘Candidatus Phytoplasma fraxini’ isolates that infect urban trees in Bogotá, Colombia

Abstract

Phytoplasmas have been associated with a disease that affects trees of at least 11 species from different botanic families in Bogotá, Colombia. ‘Candidatus Phytoplasma asteris’ and ‘Candidatus Phytoplasma fraxini’ are the major groups of phytoplasma in the area of Bogotá. In this study, the genetic diversity within ‘Ca. P. asteris’ and ‘Ca. P. fraxini’ was studied in five urban tree species: Croton species (Euphorbiaceae), Fraxinus uhdei (Oleaceae), Magnolia grandiflora (Magnoliaceae), Populus nigra (Salicaceae) and Quercus humboldtii (Fagaceae). Analyses of the 16S rRNA gene using nested PCR, RFLP and sequencing showed that phytoplasmas of ‘Ca. P. asteris’ could be assigned to: subgroup 16SrI-B; a new subgroup named 16SrI-AF, with a restriction pattern similar to that of 16SrI-B; and a new subgroup named 16SrI-AG, with a restriction pattern similar to that of 16SrI-K and 16SrI-AH with a restriction pattern similar to that of 16SrI-AC. ‘Ca. P. fraxini’ isolates belonged to a new subgroup named 16SrVII-G, with a restriction pattern similar to that of 16SrVII-A. To complement the identification of the phytoplasma strains, we amplified nonribosomal genes such as leuS and secA. Unexpectedly, it was observed that in 16 trees in which 16S rRNA gene analysis showed the presence of ‘Ca. P. fraxini’ only, the leuS or secA primers amplified sequences exclusively affiliated to ‘Ca. P. asteris. In those plants, sequences belonging to ‘Ca. P. fraxini’ leuS or secA genes were not amplified. The present work contributes to the identification of novel strains of both species in Colombia, and supports previous suggestions that phytoplasmas in South America are highly variable.