First report of a 16SrI, Candidatus Phytoplasma asteris group phytoplasma associated with a date palm disease in Saudi Arabia

Date palm (Phoenix dactylifera L.) has been affected by a disease called Al-Wijam in Saudi Arabia. The main symptoms are leaf stunting (Fig. 1), yellow streaking (Fig. 2) and a marked reduction in fruit and stalk size, which progresses to no fruit production in the final stages. A putative lethal yellowing like 16SrIV phytoplasma has previously been reported in Al-Wijam diseased palms at Al-Hassa oasis, Eastern region (El-Zayat et al., 2002). We have collected more than 30 leaf samples from palms with and without Al-Wijam symptoms and 60 Cicadellidae specimens in a survey at Al-Hassa oasis during 2003-2005.

Total DNA was extracted from plants and batches of three insects, and indexed by a nested PCR with phytoplasma generic primers P1/P7-R16F2n/R16R2. PCR products were characterized by RFLP and direct sequencing, and the 16S rDNA sequences were compared with those of other reference phytoplasmas. Phytoplasma rDNA was amplified from 28 symptomatic palms and 16 batches of insects. No PCR products were obtained from asymptomatic palms. RFLP patterns for all the PCR amplifications were identical following digestion with RsaI, HinfI, TaqI, HpaII, KpnI, DraI, HhaI and Sau3AI enzymes. The 16S rDNA sequences of the phytoplasmas identified in date palm (DQ913090) and Cicadulina bipunctata (Melichar) (DQ913091) were 100% identical and showed 98% homology to that of Aster yellows phytoplasma (AF322644) from the 16SrI, Candidatus Phytoplasma asteris group. This is the first report of a Ca. P. asteris phytoplasma associated with a disease in date palm in Saudi Arabia, and the identification of a potential vector of Al-Wijam disease, which will contribute to the future control of the disease in Al-Hassa. Further studies will be required to know the factors involved in the epidemiology of Al-Wijam disease throughout the country.