Morphological and molecular characterization of Sclerotium rolfsii associated with stem rot disease of groundnut (Arachis hypogaea L.)

Groundnut stem rot, caused by Sclerotium rolfsii , is a serious soil-borne disease. During the 2018–2019 calendar year, we aimed to characterize fungal samples that cause stem rot in groundnuts from five groundnut-growing districts of Karnataka, India. Two locations were chosen in each district, and ten fields were considered at every location. A total of 100 fields were recorded for symptoms and occurrence. Yellowing of leaves, lack of vigor, poor root growth, rotting at the stem area, and early mortality were all noticed during the survey. White, dense, fluffy, aerial, cotton-like mycelium and the growth of deep brown spherical or round sclerotia bodies were also observed around the stem and root region. In the investigated area, disease incidence ranged from 10.71 to 18.50%. Ten diseased samples were collected, each representing one site, and the pathogen was isolated and labeled as an individual isolate. To determine pathogenicity, ten isolates were inoculated on three groundnut varieties: TMV-2, GKVK-5, and GKVK-27, all of which colonized successfully. The fungal isolates had cultural and physical traits that were similar to S. rolfsii . Concatenated sequence comparisons of all ten isolates' ITS and LSU regions revealed that the current isolates have a maximum nucleotide identity of 90.10–98.80% with other known S. rolfsii isolates retrieved from the NCBI database. Similarly, the nucleotide identity of SSU ranged from 96.8 to 97.8%. Phylogenetic analysis also confirmed this, with all ten samples clustering closely with S. rolfsii isolates reported earlier.