Pathogenic and Molecular Diversity of Botryosphaeria spp. Associated with Canker and Dieback of Olive Trees

Abstract

Canker and dieback diseases of olive trees have emerged as serious constraints affecting orchard productivity and tree longevity, with Botryosphaeria species recognized as major causal agents. The present study aimed to assess the pathogenicity and molecular diversity of Botryosphaeria spp. associated with symptomatic olive branches exhibiting twig blight, bark cracking, and vascular discoloration. Fungal isolates were obtained from diseased tissues and cultured on potato dextrose agar, where they showed characteristic fast-growing, darkly pigmented colonies. Morphological examination revealed variability in conidial size, shape, and septation among isolates, suggesting species-level diversity. Pathogenicity tests on healthy olive seedlings and detached shoots confirmed the ability of all isolates to induce canker and dieback symptoms, thereby fulfilling Koch’s postulates. Molecular identification was carried out using ITS rDNA and translation elongation factor (TEF-1α) gene sequencing, which confirmed the presence of multiple Botryosphaeria and related Neofusicoccum species. Phylogenetic analysis demonstrated clear genetic clustering of isolates into distinct lineages, indicating substantial intraspecific and interspecific diversity within olive-associated populations. Variation in virulence was observed among isolates, with certain strains causing rapid lesion expansion and severe tissue necrosis. Disease development was favored by warm temperatures and water-stress conditions, which enhanced fungal colonization and host susceptibility. The study highlights the complex etiology of olive canker and dieback involving diverse Botryosphaeriaceae members and underscores the need for integrated disease management strategies. Recommended approaches include the use of disease-free planting material, pruning sanitation, canopy management, and monitoring of environmental stress factors. Overall, the findings provide important insights into the pathogenic and genetic diversity of Botryosphaeria spp. and contribute to improved understanding of olive tree decline epidemiology.