First Report of Aspergillus Niger Causing Collar Rot of Groundnut (Arachis Hypogaea L.) in Ghana

Groundnut (Arachis hypogaea L.) is a vital legume and oilseed crop of major economic importance. In Ghana, an emerging rot disease poses an increasing threat to groundnut production. This study investigated the causal pathogen of the rot symptoms observed at CSIR–Crops Research Institute, Fumesua, during the 2023 minor cropping season. Seventy-five symptomatic plants were collected from three research farms, and tissues from seed, root, and collar regions were cultured on Chloramphenicol-amended Potato Dextrose Agar (PDA). Fungal colonies initially appeared white to yellowish later turned black with yellowish margins. Microscopic examination revealed morphological features consistent with Aspergillus niger, including septate hyaline mycelia, elongated conidiophores terminating in vesicles, and brown-to-black globose conidia. Pathogenicity tests conducted using eleven isolates successfully reproduced collar rot symptoms, confirming A. niger as the causal agent, while control plants remained symptomless. The fungus re-isolated from inoculated plants exhibited morphological characteristics identical to the original isolates. The findings confirm the widespread occurrence and variable pathogenicity of A. niger in groundnut fields and highlight the need for integrated disease management strategies and the development of resistant varieties.