Molecular characterization of a 'Candidatus Phytoplasma asteris'-related strain (16SrI-B / cpn60UT I-IB) affecting daisies (Argyranthemum spp.) in Mexico

From 2018 to 2019 symptoms consistent with infection by plant pathogenic phytoplasma bacteria were observed in commercial flower greenhouses located in Atlixco, Puebla, Mexico. Two varieties of Argyranthemum spp. plants exhibited symptoms of phyllody, causing serious concerns among farmers. To determine if phytoplasmas were associated with the symptomatic plants, the 16S rRNA-encoding locus (F2nR2 fragment) was amplified by PCR. This revealed that the symptomatic plants collected were infected by a phytoplasma belonging to the aster yellows group (16SrI-B). These results were confirmed and refined by amplification and sequencing of the phytoplasma chaperonin 60 universal target (cpn60 UT). Sequence analysis using the online tool CpnClassiPhyR confirmed that the phytoplasma detected is a member of the 16SrI group, specifically a member of the cpn60 UT I-IB subgroup. This is the first report of daisies affected by phytoplasma in Mexico, and the first report of the use of CpnClassiPhyR to characterize an unknown phytoplasma strain. The detection of phytoplasmas infecting commercially produced daisies and their characterization provides an impetus for phytoplasma management in Atlixco, a Mexican city for which the production of ornamental plants and cut flowers is of economic importance.