干旱区生态环境知识资源中心

Date palm (Phoenix dactylifera L.) is one of the most important cash crops in Saudi Arabia, occupying 150,744 ha where 23 million trees produce 970,488 t of dates annually. The Eastern region is one of the most important in the country, growing date palm for centuries with more than 4 million trees located at Al-Hassa oasis. A disease called Al-Wijam has been found affecting date palm in Saudi Arabia. Main symptoms are leaf stunting, yellow streaking and a marked reduction in fruit and stalk size, which leads to failure in fruit production at harvest. Leaf samples with and without symptoms of Al-Wijam, and specimens of leafhoppers were collected in Al-Hassa oasis during 2003-2005. Total DNA was extracted from plant samples and batches of three insects and indexed by a nested PCR reaction with phytoplasma generic primers P1/P7-R16F2n/R2. PCR products were characterized by RFLP and direct sequencing. The 16S rDNA sequences were compared with those of other phytoplasmas in GenBank. Phytoplasma rDNA was amplified from 28/40 samples with symptoms of Al-Wijam and 16 insect batches. No PCR products were obtained from asymptomatic palms. RFLPpatternsforallamplicons were identical for each enzyme when digested with RsaI, HinfI, TaqI, HpalI, KpnI, DraI, HhaI and Sau3AI. The 16SrDNA sequences of the phytoplasma identified in Al-Wijam affected date palm (DQ913090) and Cicadulina bipunctata (Melichar) (DQ913091) shared 100% similarity, and had 98% similarity to that of Aster yellows phytoplasma (AF322644) a member of the 16SrI, ’Candidatus Phytoplasma asteris’ group. The identification of the phytoplasma associated and a putative vector are important contributions to our knowledge of the disease in the Al-Hassa oasis, Saudi Arabia.