‘Brittle leaf’ is a new lethal disease of date palm: addition to the EPPO Alert List
The EPPO Secretariat has recently been informed by Dr Alrouechdi (FAO/SNEA, Tunis) that an emerging disease called ‘Brittle leaf disease’ (maladie des feuilles cassantes) was causing serious damage to date palms in Tunisia. It was first described in 1986 in the oasis of Nefta (although similar symptoms were already observed in the 1960s) and has now spread to almost all oases south of Tunis. It has been found in Tozeur, Al-Hamma, Tamarza, Gafsa, Kebili and Gabes. Although the cause of the brittle leaf disease remains unknown, the EPPO Secretariat decided to add it to the EPPO Alert List because of its severity on an important crop such as date palm.
Brittle leaf disease (Maladie des feuilles cassantes - a lethal disease of date palm)
Why: A new lethal disease called brittle leaf disease (maladie des feuilles cassantes) has been reported from Tunisia since the 1960s, but is now taking alarming proportions. 36,000 trees are now affected by this disease of unknown aetiology and many other trees have already been killed and removed.
Where: Tunisia (in the south where date palm trees are growing). It has been found in Nefta, Tozeur, Al-Hamma, Tamarza, Gafsa, Kebili and Gabes. Similar symptoms have been observed in Algeria.
On which plants: Date palm (Phoenix dactylifera). The disease has been observed on most Tunisian varieties including Deglet Nour, Tozer Zaid, Akhouat Alig, Ammaria, Besser, Kinta, as well as seedling trees and pollinator trees. Kintichi seems to be relatively tolerant. No data is available on other possible hosts, for example on ornamental palms.
Damage: At the beginning, a few fronds are chlorotic with a dull, olive green colour. Leaflets become brittle, twisted, frizzled and shrivelled with a scorched appearance. The most characteristic symptom is the ease with which leaflets can be broken. Necrotic streaks develop on the pinnae. These symptoms gradually extend to the nearby fronds until the whole tree is affected, and die. 4 to 6 years may elapse between first symptoms and death of the tree. Symptoms occur on trees of all ages, including offshoots and small seedlings.
Possible cause: Symptoms resemble those of manganese deficiency, but sprays or injections of manganese do not solve the problem (at least there is a delay in symptom expression), and mineral soil analysis could not reveal differences between diseased and healthy plots. Patterns of diseased trees observed in the field suggest a biotic origin, as affected trees seem to cluster into foci. A small dsRNA has been found associated with symptomatic trees but could not be related to a known pathogen.
Pathway: Unknown. However, if pathogens (such as viroids or phytoplamas) are involved, there may be a risk associated with planting material.
Possible risks: Date palms are important crops around the Mediterranean basin, especially in Maghreb countries. The disease has apparently the ability to kill a large number of trees, and if a pathogen is involved efforts should be made to prevent any further introductions and spread.
EPPO RS 2003/091
Panel review date - Entry date 2003-06
Personal communication with Dr K. Alrouechdi (FAO/SNEA – Tunis), 2003-05.
Boletín Informativo de la Socieda Española de Fitopatología, no. 35, September 2001. http://www.sef.es/notisef_fr.htm