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Clover proliferation phytoplasma (CP R ) is designated as the reference strain for the CP phylogenetic group or subclade, on the basis of molecular analyses of genomic DNA, the 16S rRNA gene and the 16S-23S spacer region. Other strains related to CP R include alfalfa witches'-broom (AWB), brinjal little leaf (BLL), beet leafhopper-transmitted virescence (BLTV), Illinois elm yellows (ILEY), potato witches'-broom (PWB), potato yellows (PY), tomato big bud in California (TBBc) and phytoplasmas from Fragaria multicipita (FM). Phylogenetic analysis of the 16S rRNA gene sequences of BLL, CP R , FM and ILEY, together with sequences from 16 other phytoplasmas that belong to the ash yellows (AshY), jujube witches'-broom (JWB) and elm yellows (EY) groups that were available in GenBank, produced a tree on which these phytoplasmas clearly clustered as a discrete group. Three subgroups have been classified on the basis of sequence homology and the collective RFLP patterns of amplified 16S rRNA genes. AWB, BLTV, PWB and TBBc are assigned to taxonomic subgroup CP-A, FM belongs to subgroup CP-B and BLL and ILEY are assigned to subgroup CP-C. Genetic heterogeneity between different isolates of AWB, CP R and PWB has been observed from heteroduplex mobility assay analysis of amplified 16S rRNA genes and the 16S-23S spacer region. Two unique signature sequences that can be utilized to distinguish the CP group from others were present. On the basis of unique properties of the DNA from clover proliferation phytoplasma, the name 'Candidatus Phytoplasma trifolii' is proposed for the CP group.

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A phytoplasma was discovered in diseased specimens of f ield-grown hortensia (Hydrangea spp.) exhibiting typical phyllody symptoms. PCR amplification of DNA using phytoplasma specific primers detected phytoplasma DNA in all of the diseased plants examined. No phytoplasma DNA was found in healthy hortensia seedlings. RFLP patterns of amplified 165 rDNA differed from the patterns previously described for other phytoplasmas including six isolates of foreign hortensia phytoplasmas. Based on the RFLP, the Japanese Hydrangea phyllody (JHP) phytoplasma was classified as a representative of a new subgroup in the phytoplasma 165 rRNA group I (aster yellows, onion yellows, all of the previously reported hortensia phytoplasmas, and related phytoplasmas). A phylogenetic analysis of 16s rRNA gene sequences from this and other group I phytoplasmas identified the JHP phytoplasma as a member of a distinct sub-group (sub-group Id) in the phytoplasma clade of the class Mollicutes. The phylogenetic tree constructed from 165 rRNA gene sequences was consistent with the hypothesis that the JHP phytoplasma and its closest known relatives, the Australian grapevine yellows (AUSGY), Phormium yellow leaf (PYL), Stolbur of Capsicum annuum (STOL) and Vergilbungskrankheit of grapevine (VK) share a common ancestor. The unique properties of the DNA from the JHP phytoplasma clearly establish that it represents a new taxon, Candidatus Phytoplasma japonicum '.