First Report of Fusarium oxysporum Causing Fusarium Wilt on Thuja plicata in Iran

Thuja is one of the ornamental plants belonging to the conifers and Cupressales order. Coniferous trees are always important as creators of urban green spaces in terms of environmental values due to practical reasons and fast growth. In recent years, thuja wilt disease has caused irreparable damage to urban greenery, and its symptoms appear in the form of weakness and drying of the branches, which eventually causes the death of the tree. This research was conducted in order to investigate the causes of root and collar drying of thuja (Thuja plicata) in the west of Guilan province, during 2021-2022. In this study, samples were taken from the western regions of Guilan province. 40 samples were taken from the infected parts of the root and collar. After culturing the infected parts on the culture media, five fungal isolates were isolated in this study, the pathogenicity of this fungus was confirmed on potted thuja seedlings. Out of five isolates, two isolates showed wilting and rotting of the root and drying of the tips of the leaves with the same intensity of pathogenicity. These two isolates were similar in terms of their shape, and only one isolate was subjected to further laboratory work. Different cultures and molecular methods were used to identify this fungus. Based on the identification key and the molecular method, the disease-causing fungus F. oxysporum was identified.