Recent studies on the phytoplasmas associated with the Al-Wijam disease of date palm
In Saudi Arabia, a disease of date palm (Phoenix dactylifera) of unknown etiology and called ‘Al-Wijam’ was first observed in the 1950s in the oasis of Al-Hassa in the Eastern Province. The main symptoms are leaf stunting, yellow streaking (faint narrow, yellow longitudinal lines on the midribs) and a marked reduction in fruit and stalk size. In the later stages of the disease, affected date palm trees stop producing fruits and die. Since the 1980s the involvement of phytoplasmas has been suspected. In earlier studies, a putative lethal yellowing-like phytoplasma (belonging to the 16SrIV group) was reported from palm trees affected by Al-Wijam disease at Al-Hassa. Further studies have been performed more recently and a survey was carried out at the Al-Hassa oasis from 2003 to 2005. More than 30 leaf samples were collected from symptomatic and asymptomatic palms, as well as 60 specimens of Cicadellidae. Molecular studies (PCR, RFLP, DNA sequencing) revealed the presence of phytoplasma DNA in 28 symptomatic palms and in 16 batches of insects. No phytoplasma DNA was detected in asymptomatic palms. The 16S rDNA sequences of the phytoplasmas identified in date palms and Cicadulina bipunctata (Homoptera: Cicadellidae) were identical and showed 98% homology with the sequence of Aster yellows phytoplasma (belonging to the 16SrI group ‘Candidatus Phytoplasma asteris’). This is the first time that ‘Candidatus Phytoplasma asteris’ has been detected in association with the Al-Wijam disease of date palm. This is also the first time that a potential insect vector (Cicadulina bipunctata) of the Al-Wijam disease has been identified.
Sources
New Disease Reports. BSPP website (last retrieved 2007-04).
Alhudaib K, Arocha Y, Wilson M, Jones P (2007) First report of a 16SrI, Candidatus Phytoplasma asteris group phytoplasma associated with a date palm disease in Saudi Arabia. http://www.bspp.org.uk/ndr/july2007/2007-18.asp