Etiology and Pathogenicity of Diaporthe helianthi Causing Stem Canker on Sunflower in Semi-Arid Farming Regions

Abstract

Stem canker caused by Diaporthe helianthi is a destructive fungal disease affecting sunflower production in many semi-arid farming regions, where environmental stress conditions often favor disease development and reduce crop resilience. The disease is characterized by elongated stem lesions, tissue necrosis, wilting, lodging, and significant yield losses due to impaired plant growth and seed development. Accurate identification of the causal pathogen and understanding its pathogenic behavior are essential for effective disease management in sunflower cultivation systems. The present study was conducted to investigate the etiology and pathogenicity of D. helianthi associated with stem canker disease of sunflower in semi-arid agricultural regions. Diseased sunflower plants exhibiting typical stem canker symptoms were collected from affected fields, and fungal isolates were obtained using standard isolation and culturing techniques. Morphological characterization was carried out based on colony appearance, pycnidial structures, and conidial morphology. Molecular identification of representative isolates was performed through polymerase chain reaction (PCR) amplification and sequencing of conserved genomic regions, followed by phylogenetic analysis to confirm species identity. Pathogenicity assays were conducted under controlled conditions by inoculating healthy sunflower plants with fungal isolates to verify symptom development and fulfill Koch’s postulates. The results consistently associated D. helianthi with stem canker symptoms observed in infected sunflower plants. Inoculated plants developed characteristic stem lesions, tissue necrosis, and wilting symptoms similar to those observed under natural field conditions, while control plants remained symptom-free. Considerable variation in virulence was observed among isolates, with highly aggressive strains causing extensive stem damage and plant decline. Molecular sequence analysis revealed high genetic similarity between the obtained isolates and previously reported D. helianthi strains infecting sunflower in other regions.