Pathogenicity and Molecular Phylogeny of Botryosphaeria sarjaminii Causing Dieback on Grapevine in Cool Climates

Abstract

Dieback symptoms associated with stem cankers, shoot necrosis, and vascular discoloration were observed in grapevine plantations cultivated under cool climatic conditions, leading to significant decline in vine vigor and productivity. Symptomatic tissues were collected from affected vineyards, and fungal isolates were obtained through standard isolation procedures to determine the causal pathogen. Morphological characterization revealed colonies with rapid mycelial growth, dark pigmentation, and conidial features consistent with species belonging to the genus Botryosphaeria. Pathogenicity assays conducted on healthy grapevine cuttings reproduced characteristic dieback symptoms within three weeks after inoculation, whereas control plants remained symptom-free. The pathogen was successfully re-isolated from inoculated tissues, thereby fulfilling Koch’s postulates. Molecular identification based on amplification and sequencing of the internal transcribed spacer (ITS), translation elongation factor 1-α (TEF1-α), and β-tubulin gene regions confirmed the pathogen as Botryosphaeria sarjaminii. Phylogenetic analyses using maximum likelihood and neighbor-joining methods clustered the obtained isolates with reference strains of B. sarjaminii with strong bootstrap support, indicating close genetic relatedness among isolates recovered from geographically distinct vineyards. Disease severity was found to increase under prolonged cool and humid conditions, suggesting that environmental factors strongly influence pathogen establishment and disease progression. The occurrence of B. sarjaminii on grapevine represents an emerging threat to viticulture in temperate regions where climatic conditions favor fungal colonization and latent infections. Accurate identification through integrated pathogenicity and molecular phylogenetic approaches is essential for effective disease diagnosis and development of sustainable management practices.