Stilbocrea banihashemiana، یک بیمارگر نوظهور قارچی در درختان گردو

The Persian walnut (Juglans regia L.) is a globally significant tree cultivated in various regions worldwide for its valuable wood and nutritious oil. Iran, with an annual production of 355039.94 tons, stands out as one of the leading countries in this nut production. However, in recent years, walnut orchards in Fars Province have faced increasing challenges due to diseases such as canker, branch dieback, and decline. In an effort to identify the fungal agents causing these diseases, we conducted an investigation on trees in the central region of Fars Province, which exhibited symptoms like trunk and branch canker, dieback, and internal wood. Our Initial morphological analysis revealed that the fungal isolates from canker symptoms and branch dieback were associated with an emerging ascomycete pathogen, Stilbocrea banihashemiana. This pathogen has also been implicated with canker and branch dieback in fig, barberry, and loquat trees. Molecular identification of the isolates recovered from symptomatic walnut trees using species-specific primer pairs corroborated the morphological identification. We evaluated the pathogenicity of these isolates on detached branches and one-year-old walnut saplings which resulted in wood necrosis and discoloration. Cross-pathogenicity tests were conducted using S. banihashemiana isolates from walnut trees and other reported natural hosts. Interestingly, each isolate exhibited varying degrees of symptoms on different host species. Statistical analysis of four pathogenicity traits including upward, downward, and horizontal lesion progression and the depth of wood discoloration revealed distinct levels of isolate aggressiveness across different hosts. Notably, inoculated branches of walnut and loquat displayed more severe symptoms than other hosts. This study represents the first report of S. banihashemiana as the cause of branch canker and dieback in Persian walnut trees globally. Considering its potent pathogenicity on various fruit trees, identified shortly after its discovery, the unintentional development of this pathogen via the global commerce of live host plants presents a substantial risk. This threat is particularly significant for economically valuable trees across a wide range of geographical regions.