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 samples 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 group 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 cannabinum, Prunus spp., Rubus fruticosus, Vitis vinifera, and Ziziphus jujuba. RFLP profiles obtained similarly with BfaI differentiated strains from A. cannabinum and V. vinifera from other phytoplasmas of group 16SrV. Elm-associated strains from within the United States had two RFLP patterns in ribosomal DNA based on presence or absence of an RsaI site in the 16S-23S spacer. Elm-associated phytoplasma strains from Italy were distinguished from those of American origin by RFLPs obtained with MseI in the same fragment of non-ribosomal DNA. Strain HD1, which was discovered in A. cannabinum associated with EY-diseased elms in New York State, was unique among the strains studied.