Occurrence and distribution of damping-off in Vigna subterranea in Benin and identification of associated causal agents

Bambara groundnut (Vigna subterranea (L.) Verdc.), also called ground peas or Bambara groundnut, is a West African seed legume of the Fabaceae family, playing an important social and economic role. The objective of the current study was to determine the occurrence, distribution and incidence of this disease on Bambara groundnut in agroecological production zones in Benin and to identify the causal agents responsible for the damages caused to the crop. A survey was conducted from 2019 to 2020 in five agroecological zones (AEZs) of Benin (AEZ2, AEZ3, AEZ4, AEZ5 and AEZ6). A total of 30 fields of Bambara groundnut were surveyed from 10 municipalities located in the agroeclogical zones of production at the early vegetative stage of the crop. Fields’ size of 0.5 ha were selected and scouted alongside both diagonals to evaluate the damping-off disease incidence. The results showed that damping-off occurred in four out of the five AEZs surveyed. The incidence rates varied from 0.00 to 23.33% in the AEZs 5 and 6 in 2019, and from 0.00 to 18.33% in the AEZ 6 in 2020. The highest incidence rates were obtained in the West Zone of Atacora (AEZ 4) and in the Food crop region of South (AEZ 3). Results of the correlation test showed a relationship between incidence, distribution of damping-off and climatic factors. However, most of regression equations showed a strong relationship between chemical properties of soils and incidence of damping-off. Sclerotium rolfssi was identified in the laboratory as the causal agent of the damping-off disease and isolated from diseased plants in the fields and during greenhouse pathogenicity tests. To the best of our knowledge, this is the first report of identification of pathogenic fungus as the causal agent of damping-off on Bambara groundnut seedlings in Benin.