First Record of Alternaria alternata Causing Leaf Spot and Blight Disease on Ailanthus Altissima in Syria

Tree of heaven, Ailanthus altissima, is one of the invasive trees that causes great damage to the ecosystems in the regions in which it grows. At the end of August 2023, symptoms of leaf spot were observed on the spontaneously growing Ailanthus altissima on the campus of Al-Baath University, Syria. The symptoms appeared in the form of small, dark brown spots on the leaflets edges, and these spots coalesced later to become a large blighted area. The affected part may separate from the leaf edges, transforming the leaflet into a fishbone shape. The infection ultimately led to tree defoliation. Microscopic examination of infected leaves showed that the fungus causing these symptoms is Alternaria alternata: the conidia were dark brown in simple or branched chains, 25-35 micrometers in length and 9-12 micrometers in width, with 3-5 transverse septa and 1-2 longitudinal septa or no septa. Conidia collected from the infected plant were used for the pathogenicity test. According to the published information, this is the first record of Alternaria alternata on the tree of heaven in Syria and the Arab region. Keywords: Ailanthus altissima, Alternaria alternata, leaf spot, blight, first record, Syria.