Stilbocrea banihashemiana, an emerging fungal pathogen associated with canker and dieback diseases in walnut trees

Abstract

Persian walnut (Juglans regia L.), a globally significant and economically important tree, is cultivated worldwide for its valuable wood and nutritious nuts. In this study, we conducted a comprehensive survey of the trees exhibiting signs of distress, such as trunk and branch cankers, dieback, and wood discoloration, in the central region of Fars Province in Iran. Initial morphological identification indicated that the fungal isolates recovered from the canker symptoms belonged to a newly emerged ascomycete pathogen, Stilbocrea banihashemiana. The identification was further confirmed by utilizing species-specific primer pairs for S. banihashemiana. Pathogenicity assessments on detached shoots and one-year-old saplings revealed the isolates' ability to induce wood necrosis symptoms. The cross-pathogenicity test with isolates of S. banihashemiana from walnut and other reported hosts, including fig, loquat, and pomegranate was performed on detached branches. The results indicated varying levels of aggressiveness of the isolates across the different host species examined. To our knowledge, this is the first global confirmation of the isolation of S. banihashemiana from infected Persian walnut trees and the assessment of its pathogenicity on this new host.