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

item Davis, Robert
item Zhao, Yan

Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2007
Publication Date: 6/1/2008
Citation: Cai, H., Wei, W., Davis, R.E., Chen, H., Zhao, Y. 2008. Genetic diversity among phytoplasmas infecting Opuntia: virtual RFLP analysis identifies new subgroups in the peanut witches'-broom phytoplasma group. International Journal of Systematic and Evolutionary Microbiology. 58:1448-1457.

Interpretive Summary: Cacti are fleshy, evergreen plants known for their pleasing appearance, remarkable blossoms, and extreme tolerance to dry climate and poor soil conditions. Native to the Americas, many cacti have been cultivated and introduced into other parts of the world as landscaping plants and edible crops. Cacti are vulnerable to infection by phytoplasmas, which are small bacteria without a cell wall. Infection of cacti by phytoplasmas can significantly change the shape of the infected plants, impacting their commercial value. In the present study, through DNA fingerprinting analysis on diseased cactus plants collected from the province of Yunnan in southwestern China, we discovered that: (1) cacti can be infected by two distinctly different groups of phytoplasmas, (2) significant genetic diversity exists among phytoplasmas even belonging to the same group, and (3) the extent of phytoplasma genetic diversity differs, depending on geographical and ecological characteristics. Findings from this study have important implications for theories of phytoplasma evolution and for managing phytoplasma diseases in cacti and other crops. This information will be of interest to scientists and extension personnel who are concerned with phytoplasmal diseases and to regulatory agencies that are concerned with implementing new quarantine regulations.

Technical Abstract: Phytoplasmas were detected in cactus plants exhibiting witches’-broom disease symptoms in Yunnan Province, southwestern 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, eight new 16SrII subgroups were recognized, bringing the total of described group 16SrII subgroups to 13 worldwide. Geographic areas differed from one another in the extent of genetic diversity among Opuntia-infecting phytoplasma strains. The findings have implications for relationships between ecosystem distribution and emergence of group 16SrII subgroup diversity.