First Report of Agroathelia rolfsii (Sclerotium rolfsii Sacc.) Causing Basal Stem Rot Disease on Sunflower in Bangladesh

Background and Objective: Sunflower is a prime source of vegetable oils worldwide. However, these plants are vulnerable to several abiotic and biotic factors, which limit the production of the crops. The current study aimed to detect the fungal pathogen linked with basal stem rot disease of sunflowers, the effect of physical factors on fungal growth and an efficient disease management scheme including an eco-friendly approach. Materials and Methods: Sunflower stems with explicit basal rot symptoms were collected from the commercially cultivated field in the Manikganj District of Bangladesh from July, 2021 to June, 2022. A further experiment was conducted to isolate the basal stem rot fungal pathogen of sunflowers using tissue planting methods. Morphological and molecular techniques were applied to identify the causal organism. Koch’s postulates were performed to confirm the pathogenic nature of the fungus. The effect of fungal culture media, temperature, pH, bio-control agents and fungicides were evaluated against the mycelial growth of the fungus. Results: The fungus was identified as Agroathelia rolfsii (Sacc) Redhead and S.T. Mullineux (Anomorph: Sclerotium rolfsii Sacc) based on morphological and molecular characterization. A BLAST search showed the pathogenic fungus (accession number: PP577975.1) had above 95% sequence similarity with previously deposited sequences Agroathelia rolfsii (JN241559.1; MH256035.1; JN241555.1). The fungus was to thrive in all the tested culture media. The fungus preferred a wider temperature range (25-35°C). The alkaline pH conditions (8 and 9) were the most suitable for the fungus. Bio-control agent Trichoderma asperellum inhibited the mycelial growth of the fungus moderately in dual culture. Importantly, commercial fungicide carbendazim inhibited the vegetative growth of A. rolfsii completely under in vitro conditions. Conclusion: Basal stem rot of sunflowers caused by Agroathelia rolfsii, is a new record in Bangladesh. The higher temperatures and basic pH stimulate the growth and development of the fungus. Bio-control agent Trichoderma asperellum and fungicide carbendazim could be used to manage sunflower stem rot diseases.