Department of Agricultural Development, Ministry of Municipal Affairs and Agriculture, PO Box 1966, Doha-Qatar

Accepted for publication 17/03/03

Date palm (Phoenix dactylifera) is the most important fruit tree in Qatar and is also used as an ornamental or shade plant in parks, gardens and alongside roads. In November 2000, a disease occurred on date palm trees growing alongside the road of Majlis AL-Taawin located in the centre of Doha, the capital of Qatar. The disease incidence was around 10%, resulting in heavy losses. The initial symptom was a slight inclination of the area of the uppermost portion of the trunk or "neck". The mechanical weakening of the tissues in this area resulted in the neck bending-over through an angle of 180^o, until the crown pointed to the ground. Sometimes, the crown rotted-off leaving a bare trunk. An acetic, fermentative odour, characteristic of ethyl acetate emanated from the rotting tissues. Samples were collected from the infected area of affected trees, cut into 3-5 mm lengths, surface-sterilised in 1% sodium hypochlorite for 3-5 mins, then placed on potato dextrose agar (PDA) containing 50 mgL^-1 streptomycin sulfate and incubated at 25^oC for one week. The asexual stage of Ceratocystis paradoxa was isolated from all samples of diseased plants and identified by the production of two types of spores: a hyaline, cylindrical microconidia (phialospores) which formed endogenously in uniseriate chains, measuring 5-15 x 3-7 m m (Chalara state) and the dark Thielaviopsis state with ovate macroconidia measuring 11-17 x 7-15 m m.

It is likely that with date palm, C. paradoxa is an opportunistic pathogen attacking stressed trees (in the case described here, the affected trees were growing on a busy roadside location). C. paradoxa, which also infects oil palm, sugar cane, coconut and pineapple, is a widespread fungus and its pathogenicity to date palm is well-documented especially in areas where drought and salinity are prevailing (Suleman et al., 2001a; Suleman et al., 2001b). The severity of the problem was probably further exacerbated by the secondary invasion by Physiphora demandata (Diptera). Infected trees were found to be infested with P. demandata larvae. This fly is known to favour decomposing organic matter (Saaidi, 1992) and would be attracted to the rotting tissues found on trees infected with C. paradoxa.

Neck bending in date palm has been previously observed in Iraq (Abbas et al., 1992). This is the first reported observation of neck bending disease on date palm in Qatar.

The authors thank the University of Qatar, College of Sciences, (Agricultural Sciences Programme) for their kind assistance and providing the materials for isolation of the fungus during the study.

References

Abbas IH, Al-Izi MJ, Aboud HM, Saleh HM, 1997. Neck bending: a new disease affecting date palm in Iraq (Abstract). In: Proceedings of the Sixth Arab Congress of Plant Protection Congress. Beirut, Lebanon: Arab Plant Protection Society.

Saaidi M, 1992. A study of new date palm disorders in Iraq. Rome, Italy: Food and Agriculture Organization: FAO report TCP/IRQ/2255.

Suleman P, Al-Musallam A, Menezes CA, 2001a. Incidence and severity of black scorch on date palms in Kuwait. Kuwait Journal of Science and Engineering 28, 161-170.

Suleman P, Al-Musallam A, Menezes CA, 2001b. The effect of solute potential and water stress on black scorch caused by Chalara paradoxa and Chalara radiciola on date palms. Plant Disease 85, 80-83.

The British Society for Plant Pathology