Clover proliferation phytoplasma: 'Candidatus Phytoplasma trifolii'

1 Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 2 Southern Crop Protection and Food Research Center, Agriculture and Agri-Food Canada, 1391 Sandford St, London, Ontario, Canada N5V 4T3 Correspondence Chuji Hiruki chujihiruki{at}aol.com 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. Abbreviations: AAY, American aster yellows; AshY, ash yellows; AWB, alfalfa witches'-broom; AY, aster yellows; BLL, brinjal little leaf; BLTV, beet leafhopper-transmitted virescence; CP, clover proliferation; CP R , CP reference strain; CPh, clover phyllody; EAY, eastern aster yellows; EY, elm yellows; FD, flavescence dorée of grapevine; FM, Fragaria multicipita phytoplasma; HD, hemp dogbane; HMA, heteroduplex mobility assay; HV, hydrangea virescence; ILEY, Illinois elm yellows; JWB_F, jujube witches'-broom Fukui isolate; JWB_G, jujube witches'-broom Gifu isolate; JWB_Ko, jujube witches'-bro