Pathogenicity of Diaporthe spp. Isolates on Grapevine Canes and Their Molecular Phylogenetic Relationships

Abstract

Dieback and canker symptoms in grapevine plantations are increasingly associated with fungal complexes belonging to the genus Diaporthe, necessitating detailed pathogenic and phylogenetic investigations for effective disease management. Infected grapevine canes exhibiting necrotic lesions, vascular discoloration and reduced bud viability were collected from commercial vineyards for pathogen isolation. Pure cultures obtained on potato dextrose agar yielded colonies characteristic of Diaporthe spp., which were further examined using morphological traits including conidial shape, size, and pycnidial structures. Pathogenicity assays conducted on healthy detached canes and potted grapevine plants confirmed the ability of isolates to induce typical canker and dieback symptoms, thereby fulfilling Koch’s postulates. Significant variation in virulence was observed among isolates, indicating differential pathogenic potential within the population. Molecular identification based on ITS, TEF1-α and β-tubulin gene sequencing enabled precise species delineation and revealed the presence of multiple cryptic Diaporthe species associated with grapevine decline. Phylogenetic analysis clustered the isolates within well-supported clades corresponding to known pathogenic lineages reported from woody hosts, suggesting evolutionary divergence and host adaptation. Environmental conditions characterized by high humidity and moderate temperatures were found to enhance symptom development and disease progression. The study highlights the complex taxonomy and high genetic variability of Diaporthe species associated with grapevine canes. These findings emphasize the need for integrated disease management strategies involving the use of disease-free planting material, pruning hygiene, and early molecular diagnostics for rapid detection. The combined morphological and multilocus phylogenetic approach provides a robust framework for accurate identification of Diaporthe species and contributes to improved understanding of grapevine trunk disease epidemiology in viticultural systems.