New Disease Reports - First report of a phytoplasma associated with a disease of date palms in North Africa

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

P. Cronjé², A.J. Dabek¹, P. Jones*, and A.M. Tymon

Plant Pathology Department. IACR Rothamsted, Harpenden Herts., AL5 2JQ, UK. ¹FAO, Rome, Italy; ²Present address: Sugar Association Experiment Station, Mt Edgecombe, KwaZulu Natal, South Africa.

*phil.jones@bbsrc.ac.uk

Accepted for publication 03/05/2000

White tip die-back (WTD) is a newly recognised 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 (Cronjé et al., 1998) phytoplasma-specific products, 1250bp in size, were consistently amplified from WTD palms but not from healthy date palm. 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.

References

Cronje CPR, Tymon AM, Jones P, Bailey RA, 1998. Association of a phytoplasma with a yellow leaf syndrome of sugarcane in Africa. Annals of Applied Biology 133, 177-186.

Harrison NA, Richardson PA, Tsai JH, 1995. Detection and diagnosis of lethal yellowing: Conventional methods and molecular techniques. In: Oropeza C, Howard FW, Ashburner GR, eds. Lethal Yellowing: Research and Practical Aspects. Dordrecht, The Netherlands: Kluwer Academic Publishers, 79-92.