First report of a lethal yellowing phytoplasma in Thrinax radiata and Cocothrinax readii palms in the Yucatan Peninsula of Mexico

Lethal yellowing (LY) disease associated with phytoplasmas of the 16Sr IV group (now reclassified as 'Candidatus Phytoplasma palmae') has been present in the Yucatan Peninsula of Mexico for more than 25 years and has killed most of the Atlantic Tall coconut palms. Many other native palm species such as Thrinax radiate and Coccothrinax readii show no symptoms and were not considered to be susceptible. In order to determine if these palms are immune or tolerant to infection by the LY phytoplasma, trunk wood samples were collected from 10 apparently healthy palms of each species from the Yucatan coastal location of Chicxulub Puerto. Total DNA extracted from each sample was tested for phytoplasma by nested PCR, using phytoplasma universal rRNA operon primer pair P1/P7, followed by LY group-specific 16S rRNA gene primer pair LY503f/LY16Sr (Harrison et al., 1999). Phytoplasma-specific bands were amplified from five T. radiata, eight C. readii palm and LY positive controls but not from DNA from palms of both species previously identified as LY-free.

RFLP profiles obtained by digesting nested PCR products with AluI endonuclease were identical for all phytoplasma-positive palms (Fig. 1) and to that of the Florida strain of the LY phytoplasma (Harrison et al., 1999). The patterns differed from the RFLP profiles of Mexican Pacific coconut leaf yellowing strains (Harrison et al., 2002). The phytoplasma 16S rDNA sequences of PCR amplicons from T. radiata and C. readii (GenBank accessions AY919862 and AY919863) were identical to each other and to that of the LY phytoplasma (GenBank accession AF498309). The occurrence of LY phytoplasmas in these newly identified, albeit symptomless, palm hosts suggests that they could act as a permanent source of inoculum that would contribute to the epidemic in Yucatan.