Characterization and pathogenicity of fungal species associated with dieback and decline of ash trees in Ardabil and Namin County (Iran)

Ash trees (Fraxinus spp.) are one of the most important ornamental trees in the green space of cities. To evaluate the fungi associated with decline and dieback of ash trees, the symptomatic samples from branches, trunks, and roots of two species of Fraxinus (European Fraxinus, F. excelsior and Van, F. rotundifolia) were collected from Ardabil and Namin during the summer and autumn of 2018–2019. From the 60 samples, 81 fungal isolates were recovered. Based on morphological features of all isolates together with sequence data of tef-1α gene and specific primers of some Fusarium and Neocosmospora species, 21 fungal species were identified, i.e., Alternaria, Chaetomium, Clonostachys, Cytospora, Fusarium, Microascus, Microsphaeropsis, Neocosmospora, Peyronellaea and Phialophora. Neocosmospora solani, Cytospora chrysosperma and F. oxysporum had the highest abundance, respectively. Pathogenicity test was performed by excised shoot for F. cerealis, F. equiseti, F. oxysporum and N. solani excided shoot method and for C. chrysosperma on excided shoot method and also on two years old ash saplings in greenhouse. Our results showed that all examined species except F. cerealis and F. equiseti cause discoloration of wood texture at the inoculation site. According to our knowledge, most of the fungal species identified in this study, are reported for the first time on ash trees worldwide. Besides, F. denticulatum is a new record to the Iranian mycobiota.