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

Different ornamental plants showing symptoms referable to phytoplasma presence and collected between 1993 and 2015 in various floricultural areas in north and south of Italy, enclosing Sicily, resulted to be infected by ‘Candidatus Phytoplasma asteris’-related strains, and after PCR/RFLP identification on 16Sr gene were assigned to 16SrI-B subgroup. These infected samples were employed for phytoplasma strain differentiation on tuf, groel, rp and amp genes. In particular, the 23 phytoplasma strains employed were from hydrangea (5), primula (3), gentian (2), petunia (2) and gerbera (1) samples showing flower virescence; from gladiolus samples both in vivo and in micropropagation (2) showing the “germs fins” symptomatology, from statice (2) with stunting and lack of flower production, from ranunculus (2) and carnation (4) with virescence and malformation of flowers. All the genes were amplified in nested PCR except amp gene. On tuf gene all the samples were amplified, and Tru1I RFLP analyses confirmed identical profiles with those of 16SrI group phytoplasmas, however on the other genes only samples from ranunculus, gladiolus in vivo, statice and hydrangea were amplified. On these genes the phytoplasmas were identical to each other and to reference strains belonging to 16SrI-B subgroups, and after RFLP analyses carried out with Tru1I and AluI they were further enclosed in the rpI-B and GroELI-III groups. Considering that these samples were collected in different Italian regions during 22 years, the relevant conservation in the studied genotypes can be perhaps linked to the presence of common leafhopper vectors, not always identified nor detected in the cultivation areas where the diseased plants were collected. It is important to underline that ‘Ca. P. asteris’ is the prevalent phytoplasma reported in flower cultivations worldwide, and its lack of genetic polymorphisms may also indicate a globalized trading of the pathogen together with his propagation material.