Genetic diversity among phytoplasmas infecting Opuntia species: virtual RFLP analysis identifies new subgroups in the peanut witches'-broom phytoplasma group.

Phytoplasmas were detected in cactus (Opuntia species) plants exhibiting witches'-broom disease symptoms in Yunnan Province, south-western China. Comparative and phylogenetic analyses of 16S rRNA gene sequences indicated that an overwhelming majority of the cactus-infecting phytoplasmas under study belonged to the peanut witches'-broom phytoplasma group (16SrII). Genotyping through use of computer-simulated restriction fragment length polymorphism (RFLP) analysis of 16S rRNA genes revealed a remarkable genetic diversity among these cactus-infecting phytoplasma strains. Based on calculated coefficients of RFLP pattern similarities, seven new 16SrII subgroups were recognized, bringing the total of described group 16SrII subgroups to 12 worldwide. Geographical areas differed from one another in the extent of genetic diversity among cactus-infecting phytoplasma strains. The findings have implications for relationships between ecosystem distribution and the emergence of group 16SrII subgroup diversity.