First report of false smut disease caused by Graphiola phoenicis on date palm trees in Qatar

Date palm (Phoenix dactylifera) is the most important fruit tree in the State of Qatar and is widely planted in rural areas. In urban areas it is a common ornamental and shade plant, grown in parks and gardens and alongside roads. During spring and summer of 2001 and 2002, several date palm trees located in Al Ka'ban area (north Qatar) showed symptoms typical of false smut disease. The fungus results in sub-epidermal spots on both sides of the pinnae (leaflets) and on the rachis, with small, black sori developing in abundance on old fronds. Once the spores have disseminated, only the rough black craters of the sori remain. More severe infections and damage were observed in areas of higher humidity especially in Al Mashrub, located in the northeast coastal strip. Severe infection reduces tree growth and date production through premature death of leaves.

The sori were 1 to 3mm in diameter, and occurred on both sides of the pinnae, typically more abundant in the apical regions. These superficially resemble a scale insect or mealy bug infestation but closer examination revealed the exudation of powdery yellow spores on whitish filaments. The spores observed were spherical to ellipsoidal, 3-6 µm in diameter and had a thick, smooth hyaline wall. The fungus was identified as Graphiola phoenicis (Djerbi, 1983), commonly known as false smut disease. It is also known as graphiola leaf spot and palm leaf pustule.

Disease attacks were most common on seven to ten year-old palm trees and most evident on the older fronds. The disease has now spread to date palm groves throughout the country, but more quickly where trees are planted at higher densities (4-5 m spacing). False smut disease is now affecting individual date palm trees in the north, central and south areas of Qatar.

False smut disease has previously been recorded on P. dactylifera in India, Egypt and Brazil (CAB International, 2003), Libya (Edongali, 1996) and Kenya (Kung'u & Boa, 1997). This is the first report of Graphiola phoenicis occurring on date palm trees in the State of Qatar.