Abstract
Palm trees play important cultural, ecological, and economic roles in the tropics. Native palm species such as the royal palm, Roystonea borinquena O.F. Cook, are extensively planted in landscapes and urban areas of Hispaniola, Puerto Rico and the Virgin Islands. Worldwide, palms are affected by a disease commonly known as lethal yellowing, linked to the presence of phytoplasmas. Coconut Lethal Yellowing (CLY) is the most devastating disease of palms, associated with the 16SrIV phytoplasma group in the Americas. In Puerto Rico, palms displayed symptoms such as leaf chlorosis or yellowing, inflorescence and fruit necrosis, and eventual death. The objective of this research was to identify and characterize phytoplasmas in palms and their potential insect vectors, focusing on a native palm, R. borinquena. To fulfill this objective, 69 palms belonging to the species: Cocos nucifera (n=15), Gaussia attendata (n=1), Leucothrinax morrisii (n=1), Pseudophenix sargentii (n=1), Roystonea borinquena (n=50) and Washingtonia robusta (n=1) were sampled within three transects across the island. Ninety percent of palms sampled displayed typical lethal yellowing symptoms. In addition, 12 different insect species (Auchenorrhyncha: Fulgoroidea) that could act as potential phytoplasma vectors were sweep-collected from palms and grasses near the study area. The 16S ribosomal region of phytoplasmas was amplified using nested polymerase chain reaction (PCR) and subjected to restriction fragment length polymorphism (RFLP) analyses to allow their ribosomal grouping. Overall, 17 palm samples were positive to phytoplasmas. These are C. nucifera (n = 1), L. morrisii (n = 1) and R. borinquena (n = 15). Phytoplasmas detected belong to six ribosomal groups: 16SrII, 16SrIII, 16SrIV, 16SrVI, 16SrIX and 16SrX. The most frequent phytoplasma detected (59%) is enclosed in the 16SrII group. Samples from nine royal palms (R. borinquena) and one key thatch palm (L. morrisii) were positive to the 16SrII-related group. Only one insect specimen, the cixiid Haplaxius crudus collected from a phytoplasma positive R. borinquena palm, was positive for a 16SrII-related group phytoplasma. Another significant epidemiological finding was the detection of a phytoplasma related to CLY in the 16SrIV group in one individual of R. borinquena. This native species is the most abundant palm on the island. To our knowledge this is the first report of a phytoplasma related to the 16SrII group in R. borinquena in Puerto Rico and the world. Detection for the first time of other phytoplasmas related to 16Sr groups -III, -IX and -X in palms deserves further studies.