Molecular identification of fungal pathogens associated with leaf spot disease of date palms (Phoenix dactylifera)

Date palm is the most important crop in Oman, occupying approximately 50% of the area devoted to agriculture. Little information is available on leaf spot diseases of date palm in Oman and in the world. This study was conducted to identify the most common fungal pathogens associated with leaf spot diseases of date palm. A total of 198 symptomatic leaf samples were collected from seven districts in Oman. Isolations revealed that most isolates belonged to the genus Alternaria. Molecular-based identification using multigene sequences revealed that the isolates belonged to Alternaria alternata, A. burnsii, A. tomato, Curvularia subpapendorfii, Didymella microchlamydospora, Fusarium brachygibbosum, F. incarnatum-equiseti and Nigrospora lacticolonia. In pathogenicity tests, A. alternata was found to be the most aggressive. F. incarnatum-equiseti was the least aggressive, only inducing symptoms in leaves injured prior to inoculation. The other species caused moderate leaf spot symptoms on the leaves. This study shows that several fungal species belonging to different genera can be found associated with leaf spot symptoms of date palms, and they vary in their aggressiveness on date palm leaves. It is the first study to report C. verruculosa, D. microchlamydospora, and N. lacticolonia as leaf spot pathogens of date palm in the world.