Molecular characterization of a phytoplasma of the ash yellows group (16Sr VII-B) occurring in Artemisia annua and Conyza bonariensis weeds

In South America, plants infecting phytoplasmas from different 16Sr groups have been detected and characterized. Among them, 16Sr VII (ash yellows) phytoplasmas have been detected in herbaceous plants. In Brazil, EriWB and RPWB isolates infecting Erigeron sp. and Catharanthus roseus have been assigned to a new 16Sr VII-B subgroup. In Argentina, 16Sr VII subgroup C was created to enclose the ArAWB phytoplasma which infects alfalfa (Medicago sativa) plants. Recently, new isolates from the 16Sr VII group phytoplasmas have been detected in Artemisia annua and Conyza bonariensis showing typical witches' broom symptoms. The aim of this work was to perform a molecular characterization of these isolates in order to classify them and associate them to their closest relatives. A restriction analysis on PCR fragments (PCR-RFLP) from the 16S rRNA gene was performed. Sequences of three isolates were obtained to perform a cladistic analysis and to reveal their similarity to other phytoplasmas. Identical PCR-RFLP patterns, high sequence similarity (99.9%) and the cladistic grouping associated the new phytoplasma isolates infecting weeds in Argentina with the 16Sr VII-B subgroup. ArtWB strains represent geographic isolates of the EriWB phytoplasma. This work reveals the wide distribution of 16Sr VII-B phytoplasmas and their capability to infect different host plants.