The pigmy date palm (Phoenix roebelenii O'Brien) is used as an ornamental in Florida and is popular and lucrative within the nursery trade. Severe decline of several pigmy date palms was observed at a residence in Hillsborough County, FL. Several other palm species, including P. canariensis (Canary Island date palm), P. sylvestris (wild date palm), P. dactylifera (date palm), Syagrus romanzoffiana (queen palm), and Sabal palmetto (cabbage palm), in Florida are known to be affected by Texas Phoenix palm decline (TPPD), a disease associated with a phytoplasma subgroup strain 16SrIV-D (2,3). Moreover, the location of the affected pigmy date palms was in the proximity of many other diseased cabbage palms that were identified in previous surveys and subsequently rogued. Genomic DNA was extracted from 100 mg of ground-up palm trunk tissues containing phloem cells with a DNeasy Plant Mini kit column (QIAGEN Inc., Valencia, CA) from four specimens. A high-fidelity PCR (Hf-PCR) procedure was used in preference to standard PCR because it was 10,000 to 100,000 times more sensitive (1,4). The Hf-PCR (50 μl) utilized two DNA polymerases; Taq (five units) and ACCUZYME (one unit), 350 μM dNTP, a buffer (50 mM Tris pH 9.2, 16 mM ammonium sulfate, and 1.75 mM magnesium chloride), a higher concentration of primers (200 pM) (2,3), and palm DNA templates (>10 ng) or no DNA negative control. Hf-PCR was performed using three linked profiles: (i) 94°C (2 min) (1 cycle); (ii) 94°C (10 s), 50°C (30 s) for P1m/P7 or 57°C for LY16Sf/LY16Sr and 68°C (2 min) (10 cycles); and (iii) 94°C (10 s), 50°C (30 s) for P1m/P7 or 57°C for LY16Sf/LY16Sr and 68°C (2 min plus 20 s added for every consecutive cycle) (20 cycles) (1). The genomic DNA extracted from P. roebelenii specimens was used as template for amplification by Hf-PCR. Expected 1.8- and 1.4-kb DNA bands for each primer combination were readily amplified. The Hf-PCR products were sequenced (GenBank Accession No. JF791816) and a BLAST search revealed a 100% similarity with a phytoplasma subgroup strain 16SrIV-D (EF042899 and AF434989), which is known to cause severe palm decline (TPPD) in other hosts (2,3). To our knowledge, this is the first report of TPPD from P. roebelenii, and therefore, expands the host range of this pathogen. In areas where TPPD is present, the landscape industry may need to identify alternative nonhost palm species or resistant varieties for disease management.
References: (1) W. M. Barnes. Proc. Natl. Acad. Sci. USA 91:2216, 1994. (2) N. A. Harrison et al. Plant Dis. 86:676, 2002. (3) N. A. Harrison et al. Ann. Appl. Biol. 153:85, 2008. (4) A. Jeyaprakash and M. A. Hoy. Insect Mol. Biol. 9:393, 2000.