First report of Alternaria arborescens causing leaf spot on jujube (Ziziphus jujuba)

Abstract In 2024 and 2025, leaf spot symptoms were observed in a jujube ( Ziziphus jujuba ) cultivar collection in Hungary. The symptoms manifested as small, brown necrotic spots, a few millimetres in diameter, surrounded by a chlorotic margin, resembling to Alternaria leaf spot. The pathogen was successfully isolated from symptomatic leaves, and was identified as a member of the Alternaria arborescense species complex through morphological characterization and multilocus phylogenetic analysis targeting the ITS, TEF1-α , and Rpb2 gene regions. Artificial inoculations of detached jujube leaves and seedlings reproduced the characteristic disease symptoms, and subsequent reisolation of the fungus fulfilled Koch’s postulates, confirming its pathogenicity. Hence, this study represents the first report of A. arborescense causing jujube leaf spot. The potential impact of A. arborescens on jujube production and the increasing prevalence of Alternaria leaf spot diseases under the changing climatic conditions, underscore the need for further research.