Molecular properties of Texas Phoenix decline phytoplasma, a subgroup 16SrIV-D strain associated with lethal diseases of Sabal palmetto and other palms in Florida

A decline of sabal or cabbage palm (Sabal palmetto) with symptoms similar to those of coconut (Cocos nucifera) lethal yellowing (LY) was first observed in west central Florida, USA in 2008. Characterization of the causal agent implicated a phytoplasma, which closely resembled a subgroup 16SrIV-D phytoplasma previously associated with declining Canary Island date palms (Phoenix canariensis), edible date (P. dactylifera), silver date (P. sylvestris) and Queen (Syagrus romanzoffiana) palms. The phytoplasma strain associated with the Florida native S. palmetto was therefore also referred to as Texas Phoenix decline (TPD) phytoplasma, and classified as a subgroup 16SrIV-D strain. Although this phytoplasma had been classified based on the 16S rRNA sequence, further characterization of its genome remained crucial. Twenty five S. palmetto plants in west central Florida showing symptoms of decline were selected for sampling of the phytoplasma associated with the disease. DNA was extracted from tissue samples and the intergenic spacer region between 16S rRNA and 23S rRNA genes was amplified by a nested polymerase chain reaction assay. The sequence of the 16S-23S intergenic spacer (IGS) of TPD phytoplasma infecting S. palmetto was compared with IGS sequences derived from six 16SrIV-D phytoplasma strains infecting Phoenix spp., a 16SrIV-D strain infecting Syagrus romanzoffiana, a 16SrIV-F strain infecting Washingtonia robusta, two strains each comprising a mixture of 16SrIV-A and 16SrIV-F phytoplasmas, one LY phytoplasma strain from P. canariensis and finally those of three 16SrIV-A strains associated with LY disease of C. nucifera. The TPD phytoplasma population associated with S. palmetto appears homogenous. On the basis of the ribosomal operon, the TPD phytoplasma in S. palmetto is similar to other TPD strains found in Phoenix spp. and S. romanzoffiana, but different from the subgroup 16SrIV-A phytoplasma associated with C. nucifera and Phoenix spp. For further analysis, three genes were selected: the nusA gene, the hflB gene, and the gcp gene. All genes (nusA, hflB and gcp) differentiated the strains in this study similarly, TPD phytoplasma strain infecting S. palmetto is similar to the TPD strain infecting Cocos and Phoenix spp. but different from the LY strains associated with C. nucifera.