Submitted to: International Citrus Congress Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 7/31/2012
Publication Date: 11/18/2012
Citation: Wang, X., Doddapaneni, H., Chen, J., Yokomi, R.K. 2012. Genetic variation of Spiroplasma citri populations in California revealed by two genomic loci . International Citrus Congress Proceedings. S12P35, p. 213. Interpretive Summary:
Technical Abstract: Citrus stubborn disease (CSD), known to be present in California since 1915, was confirmed to be caused by Spiroplasma citri in 1972. Hosts of S. citri include citrus and a wide range of annual weeds, ornamentals and crops such as carrots and sesame. Genetic variation of S. citri in California was evaluated previously by RAPD-PCR with 20 primer pairs but no unique genetic signatures were found. Using partial chromosome sequences and plasmid sequences of S. citri recently released in GenBank, a conserved hypothetic peptidyl-arginine deiminase protein (PADP) and a transmembrane protein (TMP) of plectrovirus spv1-r8a2b were selected in silico to evaluate genetic diversity of S. citri from different hosts and locations. Two specific primer sets were selected. The first was called PADP and targeted a region with variable tandem repeat numbers (TRNs); the second was TMP which was based on multiplex sizes in different contigs in GII3-3X. A panel of 31 strains of S. citri from California, Illinois and the Mediterranean region were evaluated using the two primer sets by PCR. Electrophoretic profiles of PCR amplicons from the strains tested consistently showed three TRN patterns in the PADP locus and three from the TMP locus. Interestingly, the strains which showed a different profile at PADP also showed a different profile at the TMP and matched each other as a set. Sequence analyses conducted amongst strains in each pattern group revealed at least three genotypes were present in California S. citri populations. Further study of field strains from different geographical origins using the two loci described should provide insight into the biology and epidemiology of S. citri.