In Vitro Antibacterial Activity and Phytochemical Characterization of Ricinus Communis and Cajanus Cajan Leaf Extracts Against the Causal Agent of Bacterial Wilt

Bacterial wilt caused by the Ralstonia solanacearum species complex is a major crop constraint. However, considering the limitations of conventional control methods and the environmental challenges associated with the excessive use of synthetic pesticides, exploring plant-based biopesticides appears to be a promising alternative strategy for sustainable management. It is in this context that the present study was initiated to evaluate the in vitro antibacterial potential and characterize the phytochemical profile of aqueous extracts and fermented leaf extracts from Cajanus cajan and two varieties of Ricinus communis against Ralstonia solanacearum species complex. The extracts were prepared from the leaves and then tested using the agar diffusion method to assess their antibacterial activity, compared with the reference biopesticide NECO 50 EC and chloramphenicol. Qualitative phytochemical sorting was also performed to identify the main groups of secondary metabolites present in the extracts and fermented extracts. Most of the tested aqueous extracts and fermented extracts exhibited antibacterial activity after 24 h of incubation, except for R. communis var. zanzibarensis aqueous extract. The best antimicrobial activities were obtained using the biopesticide NECO 50 EC (22,01 mm) and chloramphenicol (27,98 mm). Fermented extract of C. cajan showed consistent inhibition of bacterial growth at all concentrations, with diameters ranging from 9 to 14 mm. However, the antibacterial activity of the extracts was unstable over time, unlike on the positive controls, whose effect was constant. Phytochemical sorting revealed several groups of bioactive compounds in the aqueous extracts, whereas the fermented extracts contained only polyphenols. The antibacterial potential of C. cajan and R. communis extracts against the Ralstonia solanacearum species complex was demonstrated, in line with their richness in secondary metabolites. However, the temporal instability of their activity highlights the need for further research to explore their potential use in sustainable agriculture.