Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2017
Publication Date: 8/1/2017
Citation: Davis, R.E., Zhao, Y., Wei, W., Dally, E.L., Lee, I. 2017. ‘Candidatus Phytoplasma luffae’, a novel taxon associated with a witches’-broom disease of loofah, Luffa aegyptica Mill. International Journal of Systematic and Evolutionary Microbiology. 67:3127-3133. 10.1099/ijsem.0.001980.
Interpretive Summary: Phytoplasmas are minute bacteria that are the causes of damaging diseases of crop plants and plants in natural habitats worldwide. Because phytoplasmas that occur outside of North America could possibly pose a threat to US agriculture, it is important to prevent these “exotic” phytoplasmas from entering the USA. One such phytoplasma causes disease in plants of luffa (loofah) growing in Asia. We have identified this phytoplasma by a specific name and obtained precise molecular markers for its identification. Our work will facilitate quarantine measures designed to prevent spread of the phytoplasma across national borders. Using molecular methods to study specific genes, we found that the loofah phytoplasma represents a previously undescribed species, for which we have proposed the designation, ‘Candidatus Phytoplasma luffae’. Our results provide genome-based molecular markers by which ‘Candidatus Phytoplasma luffae’ may be detected and identified, benefitting implementation of quarantine measures to prevent its spread. Such progress will aid the cause of food security and sustainable agricultural production. This report will be of interest to diagnostics laboratories, research scientists, farmers, and quarantine agencies internationally.
Technical Abstract: The phytoplasma associated with witches’ broom disease of loofah (Luffa aegyptica Mill., syn. L.uffa cylindrica (L.) M.J. Roem.) in Taiwan was classified in group 16SrVIII, subgroup A (16SrVIII-A), based on results from actual and in silico RFLP analysis of 16S rRNA gene sequences. Nucleotide sequencing of PCR-amplified, cloned DNA segments revealed rrn interoperon sequence heterogeneity in the loofah witches’ broom (LfWB) phytoplasma. Whereas the 16S-23S rRNA spacer region of rrnA contained a complete tRNA-Ile gene, the spacer of rrnB contained a nonfunctional remnant of a tRNA gene. Phylogenetic analysis of the rrnA and rrnB 16S rRNA genes revealed that the loofah witches’ broom (LfWB) phytoplasma represented a distinct lineage within the phytoplasma clade, and the LfWB phytoplasma shared less than 97.5% nucleotide sequence similarity of 16S rRNA genes with previously described ‘Candidatus Phytoplasma’ taxa. Based on unique properties of DNA, we propose recognition of loofah witches’ broom phytoplasma strain LfWBR as representative of a novel taxon, ‘Candidatus Phytoplasma luffae’.