Multilocus sequences confirm the close genetic relationship of four phytoplasmas of peanut witches'-broom group 16SrII-A

Four witches'-broom diseases associated with Arachis hypogaea (peanut), Crotalaria pallida, Tephrosia purpurea, and Cleome viscosa were observed in Hainan Province, China during field surveys in 2004, 2005, and 2007. In previously reported studies, we identified these four phytoplasmas as members of subgroup 16SrII-A, and discovered that their 16S rRNA gene sequences were 99.9-100% identical to one another. In this study, we performed extensive phylogenetic analyses to elucidate relationships among them. We analyzed sequences of the 16S rRNA gene and rplV-rpsC, rpoB, gyrB, dnaK, dnaJ, recA, and secY combined sequence data from two strains each of the four phytoplasmas from Hainan province, as well as strains of peanut witches'-broom from Taiwan (PnWB-TW), "Candidatus Phytoplasma australiense", "Ca. Phytoplasma mali AT", aster yellows witches'-broom phytoplasma AYWB, and onion yellows phytoplasma OY-M. In the 16S rRNA phylogenetic tree, the eight Hainan strains form a clade with PnWB-TW. Analysis of the seven concatenated gene regions indicated that the four phytoplasmas collected from Hainan province cluster most closely with one another, but are closely related to PnWB-TW. The results of field survey and phylogenetic analysis indicated that Cr. pallida, T. purpurea, and Cl. viscosa may be natural plant hosts of peanut witches'-broom phytoplasma.