Black Stem of Sunflower: An Emerging Fungal Disease Caused by Fusarium solani in Bangladesh

Background and Objective: Sunflower is one of the world's most important oil seed crops. However, these crops are prone to biotic factors, which reduce the yield of the crops. The present experiment was designed to identify and assess the growth characteristics of the fungal pathogens associated with the black stem disease of sunflowers and its control measures in Bangladesh. Materials and Methods: Both morphological features and molecular characterization based on the rDNA ITS region of the fungus were employed to identify the fungal pathogen. Six distinct solid fungal culture media, five separate temperature ranges and five different pH levels of medium were used to assess the mycelial growth behavior of the isolated fungus. Selected biocontrol agents and chemical fungicides were employed against the fungus under in vitro conditions. Results: The BLASTn search on the NCBI database revealed that the fungal pathogen (accession number: PP573854.1) showed above 99% homology with previously deposited sequences of Fusarium solani. Koch’s postulate test was conducted to prove the pathogenicity. The fungal culture media, Potato Sucrose Agar and Carrot Agar exhibited the maximum mycelial growth. The vegetative growth of the fungus was most favored at 30°C temperature. Besides, slightly acidic conditions were mostly preferred by the F. solani. Among the fungal antagonists, Trichoderma erinaceum inhibited the maximum (81%) of the mycelial growth of the targeted fungus, followed by 73% for Trichoderma harzianum. Fungicides Amistar Top 325 SC and copper blue 50 WG showed above 70% growth inhibition against the vegetative growth under in vitro conditions. Conclusion: Biocontrol agents and synthetic fungicides will be promising options to control the black stem diseases of sunflowers. Black stem disease on sunflowers caused by Fusarium solani is a new record in Bangladesh.