Multilocus typing for characterization of ‘Candidatus Phytoplasma asteris’-related strains in several ornamental species in Italy

Different ornamental plants showing symptoms indicating phytoplasmapresence were collected between 1993 and 2016 in various floricultural areas innorth and south of Italy, including Sicily. These samples were determined to beinfected by ‘Candidatus Phytoplasma asteris’-related strains, and after PCR/RFLPidentification based on the 16S rRNA gene were assigned to the 16SrI-B subgroup.These infected samples were employed for phytoplasma strain differentiation on tuf,groel, rp and amp genes. Phytoplasma strains were from hydrangea, primula,Centaurium erythraea, petunia and gerbera samples showing flower virescence; fromgladiolus samples both in vivo and in micropropagation showing the “germs fins”symptomatology, from statice with stunting and lack of flower production, fromranunculus and carnation with virescence and malformation of flowers. All the geneswere amplified in nested PCR except the amp gene. For the tuf gene all samplesresulted amplified, and Tru1I RFLP analyses confirmed identical profiles with those of16SrI group phytoplasmas. However, for the other genes only samples fromranunculus, gladiolus in vivo, statice and hydrangea were amplified. For these genesthe phytoplasmas were identical to each other and to reference strains belonging to16SrI-B subgroups; RFLP analyses with Tru1I and AluI further indicated placement inthe rpI-B and GroELI-III groups. Considering that these samples have been collected indifferent Italian regions during 23 years, the relevant conservation in the studiedgenotypes can perhaps be linked to the presence of common leafhopper vectors, notalways identified nor detected in the cultivation areas where the diseased plants werecollected. It is important to highlight that ‘Ca. P. asteris’ is the prevalent phytoplasmareported in flower cultivations worldwide, and its lack of genetic polymorphisms mayalso indicate a globalized trading of the pathogen together with its propagationmaterial.