First report of a phytoplasma-associated lethal decline of Sabal palmetto in Florida, USA

Sabal or cabbage palm (Sabal palmetto) occurs naturally in abundance throughout Florida where it is also a widely used ornamental in landscape plantings. Declining sabals characterized by unusually large numbers of reddish-brown leaves in the lower and mid-crown (Fig. 1), together with wilting and necrosis of the youngest(spear) leaf, were first observed in Manatee and Hillsborough counties of west-central Florida during May 2008. Discovery of this newly-affected palm species was preceded by a recent report of five other palm species affected by lethal yellowing (LY)-type diseases attributed to group 16SrIV phytoplasmas in this part of the state (Harrison et al., 2008). On this basis, tissues were removed from basal stems of 18 sabal palms with pronounced foliar discoloration and analyzed for phytoplasma infection by a nested PCR assay using primer pairs P1m/LY16-23Sr followed by LY16Sf2/LY16-23Sr2, as previously described (Harrison et al., 2008). An rDNA amplicon (1.6 kb) was obtained from 15 of 18 palms. A similar product was also amplified from DNA of a Chinese fan palm (Livistona chinensis) with LY symptoms, but not from DNA of a symptomless sabal palm both sampled in Broward county, southeastern Florida and included as positive and negative controls in each assay.

Restriction fragment profiles after digestion of nested rDNA products with BstUI, HhaI (Fig. 2A) or MseI and MspI (Fig. 2B) endonuclease revealed no differences among phytoplasmas detected in symptomatic sabal palms indicating that these palms contained very similar or, possibly, the same phytoplasma. Collectively, profiles also clearly differentiated these strains from the LY phytoplasma-positive control, a known subgroup 16SrIV-A strain (Harrison et al., 2002a). Sequencing and phylogenetic analysis of 16S rDNA from sabal palm phytoplasma RWSP (GenBank Accession No. FJ217386) determined this strain to be coidentical with subgroup 16SrIV-D strains associated with lethal declines of Phoenix palms (EU096499, EU241518) and Syagrus romanozoffiana (EU241513) in west-central Florida (Harrison et al., 2008) or Phoenix canariensis (AF434989) in southern Texas (Harrison et al., 2002b). This is a first report of a phytoplasma disease affecting native S. palmetto in the USA.