Taxonomy and Pathogenicity of Lasiodiplodia Species Associated with Dieback and Canker of Pistachio

Abstract

Taxonomy and pathogenicity of Lasiodiplodia species associated with dieback and canker of pistachio were investigated to clarify species diversity, distribution, and their role in disease development. Field surveys were conducted in pistachio orchards showing symptoms of branch dieback, bark cracking, vascular discoloration, and canker formation. Fungal isolates were obtained from symptomatic tissues and characterized based on colony morphology, conidial features, and growth patterns. Molecular identification was performed using ITS rDNA and β-tubulin gene sequencing to resolve species-level identity and assess phylogenetic relationships. Results revealed the presence of multiple Lasiodiplodia species complexes associated with pistachio decline, indicating a diverse and genetically variable pathogen population. Phylogenetic analysis showed clear clustering of isolates into distinct species groups, suggesting both species-level diversity and regional differentiation. Pathogenicity tests on detached shoots and young plants demonstrated significant variation in virulence among isolates, with highly aggressive strains inducing rapid lesion expansion, canker formation, and twig dieback. Environmental stress conditions were found to enhance disease severity and symptom expression. The study highlights the importance of accurate molecular taxonomy in distinguishing cryptic Lasiodiplodia species and understanding their epidemiological roles. These findings provide a foundation for developing effective disease management strategies, including sanitation pruning, monitoring of latent infections, and deployment of resistant germplasm in pistachio production systems.