During a survey in 2016–2020, the symptoms of decline were observed on walnut trees in some of the provinces in Iran. The most common symptoms were sudden wilting, yellowing of the leaves and necrotic lesions of woody tissues surrounding the Zeu- zera pyrina damage in the walnut orchards. In the cross-section of the stems, V-shaped necrosis and brown discolorations were observed adjacent to larval galleries of Z. pyrina. Generally, the decline is considered a complex disease caused by interacting abiotic and biotic agents. In order to identify the possible causative agent of V-shaped necrosis, sampling was conducted from symptomatic trees in the main walnut-growing provinces of Iran. After isolation using the standard method on potato dextrose agar (PDA) medium and purication, 67 fungal isolates were obtained from symptomatic tissues. The common occurrence of similar fungal isolates in symptomatic tissues of walnut trees called into question the identity of this fungus. Assessment of mor- phological and cultural characteristics along with analysis of ITS region sequences showed that these isolates were Kalmusia variispora. The results of pathogenicity tests conrmed that K. variispora to be pathogenic on walnut trees. To our knowledge, this study is the rst to present insights into K. variispora associated with the decline of walnut trees in the worl
