31 Journal of Nuts Journal homepage: ijnrs.damghaniau.ac.ir Journal of Nuts 13(1) (2022) 31-39 ORIGINAL ARTICLE Neoscytalidium dimidiatum as One of the Fungal Agents Associated with Walnut Decline in Iran Shima Bagherabadi 1 , Doustmorad Zafari *1 , Sajeewa S. N. Maharachchikumbura 2 1 Department of Plant Protection, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran 2 School of Life Science and Technology, University of Electronic Science and Technology China, Chengdu 15 611731, People’s Republic of China A R T I C L E I N F O A B S T R A C T Keywords: Botryosphaeriaceae; Canker; Dieback; Juglans regia; Sooty canker Walnut (Juglans regia L.) is one of the main nutritional nut crops in many parts of the world. Iran is one of the most important countries in the world regarding walnut production. In recent years, dieback and decline of some of walnut trees has attracted the attention of growers and plant pathologists in Iran. Although the infestation by the Cytospora spp. was accepted as the causal agent of canker, dieback, and decline in walnut trees, the role of the other agents has yet to be well investigated. Field observations were conducted during 2016- 2020 from different provinces in Iran, and black sooty canker was noticed in most declined or declining walnut trees. To determine the causal agent of the observed symptoms, sampling was conducted, and fungal isolates were obtained from symptomatic tissues of walnut trees. The fungus consistently isolated was identified as Neoscytalidium dimidiatum based on morphological and molecular characteristics of the ITS and tef1-α regions. Neoscytalidium dimidiatum was shown to be the cause of the symptoms by pathogenicity testing. The current findings show that N. dimidiatum is a serious and devastating disease in Iran, causing walnut tree decline. Introduction Persian walnut (Juglans regia L.), one of the major nut crops in the family Juglandaceae, is a valuable tree that is found in several parts of the world (Mousivand et al., 2013; Sarikhani et al., 2021; Thapa et al., 2021). It is the second- most important edible nut crop grown in Iran, the third- largest walnut producer globally (Hassani et al., 2020). Walnut is a worth crop that is generally consumed (Akca and Sahin, 2022). Not only nuts but also all components of walnuts are being used in both cosmetic and pharmaceutical industries (Vahdati et al., 2018). Being sessile, plants are often exposed to the soil-born pathogens of contaminated soils or other sources of pathogens (Aoko et al., 2021). The walnut trees are infected by a wide range of fungal and bacterial pathogens (Khodadadi et al., 2016; Farr and Rossman, 2021). Among them, branch and trunk canker diseases have become prevalent on nut crops (Gramaje et al., 2016). Species of Cytospora are one of the most important fungal pathogens associated with walnut canker disease in the world (Fan et al., 2015). Cytospora canker caused by the fungus Cytospora spp. is one of the most common diseases of walnut trees in many parts of Iran. The disease typically attacks walnut branches and leads to large areas of dieback (Abbasi et al., 2013). The decline is a multidimensional and complex phenomenon and is caused by a broad range of plant pathogens. The severity of symptoms, when the disease occurs, is driven by several factors that take place simultaneously or frequently. Although infestation by the Cytospora spp was accepted as * Corresponding author: Email address: zafari_d@yahoo.com Received: 17 November 2021; Received in revised form: 15 December 2021; Accepted: 3 January 2022 DOI: 10.22034/jon.2021.1945165.1142