First report of Graphium carbonarium associated with walnut dieback in Iran

Walnut tree is one of the most important nut crops in Iran. Dieback and decline of walnut trees are some of the factors limiting the cultivation and sustainability of this crop. During 2017 and 2018, field surveys were conducted on walnut orchards in Yazd province to study of fungal pathogens associated with diseased trees. Wood samples were collected from diseased branches showing canker, dieback and gumming symptoms. In the laboratory, affected branches were cut transversally and infected wood tissues were cut into small pieces. Wood pieces were plated on a potato-dextrose-agar (PDA) after surface sterilization. In this study, 10 isolates of a fungus were obtained from affected trees. Based on morphological and molecular (for two selected Iranian isolates based on ITS-rDNA and tef1-α gene sequences) characteristics, all isolates were identified as Graphium carbonarium. Based on literature reviews, this is the first report of this species associated with necrotic wood of walnut trees in the world.