Phytoplasmas associated with elm yellows: Molecular variability and differentiation from related organisms

Restriction fragment length polymorphism (RFLP) analyses were performed on polymerase chain reaction (PCR) amplimers of phytoplasmal DNA from eight sa mples obtained from Ulmus spp. (elms) affected by elm yellows (EY) in Italy and the United States, from Catharanthus roseus infected with strain EY1, and from five other plant species infected with phytoplasmas of the EY grou p sensu late (group 16SrV). RFLP profiles obtained with restriction enzyme TaqI from ribosomal DNA amplified with primer pair P1/P7 differentiated elm -associated phytoplasmas from strains originally detected in Apocynum canna binum, Prunus spp., Rubus fruticosus, Vitis vinifera, and Ziziphus jujuba. RFLP profiles obtained similarly with BfaI differentiated strains from A. c annabinum and V. vinifera from other phytoplasmas of group 16SrV. Elm-assoc iated strains from within the United States had two RFLP patterns in riboso mal DNA based on presence or absence of an RsaI site in the 16S-23S spacer. Elm-associated phytoplasma strains from Italy were distinguished from thos e of American origin by RFLPs obtained with MseI in the same fragment of no n-ribosomal DNA. Strain HD1, which was discovered in A. cannabinum associat ed with EY-diseased elms in New York State, was unique among the strains st udied.