First Report of a 16SrII Group Phytoplasma Associated with Shoot Proliferation of a Cactus (Opuntia monacantha) in Lebanon.

Abstract

In October 2003, during a survey to evaluate the incidence of phytoplasma diseases in Lebanon, symptoms suggestive of phytoplasma infection in Opuntia monacantha (Haworth) were observed in Saghbine, Bekaa Valley. Symptoms were excessive stem and shoot proliferation. Three symptomatic and as well as symptomless plants were collected and analyzed for the presence of phytoplasmas. Nucleic acids were extracted from 0.5 g of shoot tissue and tested using polymerase chain reaction (PCR) with universal phytoplasma primers (fU5rU3) for partial amplification of the ribosomal 16SrDNA (4). PCR resulted in amplification of an expected 881-bp rDNA fragment from the symptomatic but not from symptomless samples. For characterization, sequence of the amplified DNA was determined (Genbank Accession No. AY939815). The sequence showed a high similarity with several isolates of the 16srII group of phytoplasmas. The highest similarity has been oserved with 16S rDNA of two isolates of cactus witches'-broom phytoplasma found in China (1) and Mexico (3) (Genbank Accession Nos. AJ293216 and AF320575, respectively) (99.8%) as well as faba bean phyllody phytoplasma (Genbank Accession No. X83432) (99.7%) and "Candidatus Phytoplasma aurantifolia" (Genbank Accession No. U15442) (99.3%). The presence of phytoplasmas was confirmed using nested-PCR with primers R16mF2/R1 and R16F2n/R2 (2). The Tru9I digestion pattern of the amplified product R16F2n/F16R2 detected in O. monacantha was identical to the digestion pattern obtained from periwinkle infected by "Ca. P. aurantifolia" (subgroup 16SrII-B) and soybean phyllody phytoplasma (subgroup 16SrII-C), but different from the Tru9I digestion pattern observed for cleome phyllody phytoplasma (subgroup 16SrII-A) and tomato big bud phytoplasma (subgroup 16SrII-E). To our knowledge, this is the first report of an infection with a phytoplasma belonging to16SrII group in Lebanon.