Occurrence and Pathogenicity of Neofusicoccum Species Associated with Canker and Dieback of Walnut Trees

Abstract

Occurrence and pathogenicity of Neofusicoccum species associated with canker and dieback of walnut trees were investigated to determine species composition, distribution, and disease-causing potential in orchard ecosystems. Field surveys were conducted in walnut-growing regions, and symptomatic branches exhibiting cankers, bark discoloration, vascular necrosis, and dieback were collected for fungal isolation. Morphological characterization was based on colony growth patterns, conidial morphology, and pigmentation on culture media, while molecular identification was confirmed through ITS rDNA sequencing and phylogenetic analysis. Results revealed the presence of multiple Neofusicoccum species associated with walnut decline, indicating a complex etiology of the disease. Phylogenetic analysis showed clear clustering of isolates into distinct species groups, reflecting genetic diversity within the pathogen population. Pathogenicity tests on detached shoots and young walnut seedlings demonstrated significant variation in virulence, with highly aggressive isolates causing rapid lesion expansion, girdling cankers, and severe dieback symptoms. Environmental factors such as temperature and host stress conditions were found to influence disease expression and severity. The study highlights the role of latent infection and endophytic behavior in disease development, enabling the pathogen to persist in asymptomatic plant tissues. These findings emphasize the importance of accurate molecular identification and virulence assessment for effective management of walnut canker and dieback diseases. Integrated management strategies, including sanitation pruning and monitoring of latent infections, are essential to reduce losses in walnut production systems.