A novel Agroathelia species causing southern blight on Aconitum carmichaelii in Sichuan, China

Aconitum carmichaelii is a prominent medicinal plant widely used in Asian countries. Southern blight is one of the main soilborne diseases and has severely restricted the sustainable development of A. carmichaelii. Its causative pathogen was identified as Sclerotium rolfsii in 1981 in the main planting areas. Typical southern blight symptoms were observed on A. carmichaelii in Jiangyou, Sichuan, China, from 2020 to 2023, and five fungal strains were isolated from diseased A. carmichaelii plants. Fungal isolates formed white, fluffy, cotton-like mycelium and dark brown, round or oval sclerotia. The lethal temperature for these isolates was 55 degrees C, while they showed various resistant capacities against acid, alkaline and salt conditions and fungicides. Starch and ammonium chloride were the optimal carbon and nitrogen sources for the fungal isolates, respectively. Phylogenetic analysis based on concatenated sequences of rDNA internal transcribed spacer (ITS), large subunit (LSU) and beta-tubulin (TUB) revealed that these five isolates clustered independently into the Agroathelia clade but with <97% identity to reference strains and were characterized as Agroathelia sp. nov. Inoculation of fungal hyphal plugs on A. carmichaelii roots and plants caused severe southern blight symptoms. Cross-pathogenicity tests demonstrated that the five isolates also displayed high pathogenicity on eggplant and tomato plants. These findings provide valuable insights into a novel southern blight pathogen of A. carmichaelii that may contribute to effective management of this disease.