Identification and characterization of the phytoplasma associated with elm yellows in southern Italy and its relatedness to other phytoplasmas of the elm yellows group

In the neighbouring regions Basilicata, Campania, and Calabria of southern Italy, diseased trees of European field elm (Ulmus minor) were examined for phytoplasmal infection using polymerase chain reaction (PCR) technology. All affected trees examined tested positively. Using a primer pair specific for the EY phytoplasma group and restriction fragment length polymorphism (RFLP) analysis of PCR-amplified ribosomal DNA, the organism detected was identified as the elm yellows (EY) phytoplasma. RFLP analysis of PCR-amplified ribosomal DNA was also employed to attempt differentiation within the EY group which includes, in addition to the EY agent, phytoplasmas infecting Rubus, alder, eucalypts, Spanish broom, and grapevine. Following separate digestion with AluI, RsaI, Sau3AI, MseI, HhaI, and KpnI, all PCR-products from EY-group phytoplasmas examined had similar RFLP profiles. When the same ribosomal DNA fragments were digested with TaqI restriction endonuclease, three different restriction profiles were detected among the EY-group phytoplasmas. These profiles represented, respectively, (1) the EY phytoplasma (2) the phytoplasmas causing rubus stunt and being associated with alder yellows, spartium witches broom, and eucalyptus little leaf, and (3) the flavescence dorée phytoplasma. RFLP analysis using TaqI endonuclease enabled for the first time the differentiation of the phytoplasmas associated with alder yellows, eucalyptus little leaf, and spartium witches broom from the EY agent.