First report of a phytoplasma associated with a disease of date palms in North Africa

Abstract

White tip die-back (WTD) is a newly recognized disease of young date palms (Phoenix dactylifera L.) in northern Sudan and occurs in scattered foci throughout the region. It affects immature palms, 5–8 years old, which die within 6–12 months of symptom appearance. Symptoms appear as a severe chlorosis of the emerging spear leaf and at the tips of the pinnae of older fronds. Chlorotic streaks, mainly white with some necrosis, extend longitudinally along the sides of the frond mid-rib. There is no yellowing of the crown, which changes quickly from green to dry white. No phytoplasmas could be unequivocally identified by electron microscopy in the WTD-affected date palm tissues. Using a nested polymerase chain reaction together with general phytoplasma primers which amplify the 16S/23S rDNA (Cronjéet al., 1998), phytoplasma-specific products, 1250 bp in size, were consistently amplified from WTD palms but not from healthy date palms. The phytoplasma 16S/23S rDNA intergenic spacer region was sequenced and this showed a very high (99%) homology with comparable sequences of Bermuda grass white leaf (BGWL) phytoplasma strains from South-east Asia and Sudan (GenBank accession numbers: Y14645, AF100412). Further studies will be needed to establish if there is a connection between this date palm disease and the presence of BGWL in plantations. The 16S/23S spacer sequence from WTD date palm has been submitted to GenBank (accession number: AF 100411). Date palms are known to be susceptible to the lethal yellowing phytoplasma in the USA (Harrison et al., 1995), but there are no previous records for their susceptibility to phytoplasma infection in countries outside the lethal yellowing zone.