Medicinal Plants as Biocontrol Agents: An In Vitro Study on Black Rot Pathogen of Cabbage (Xanthomonas campestris pv. campestris)

Black rot in cabbage caused by Xanthomonas campestris pv. campestris is the most common yield-limiting and damaging disease affecting crucifers. The application of chemicals has hazardous effects on the soil and environment. To test bio-based alternatives for chemicals, extracts of 10 medicinal plants (royal poinciana, ivy gourd, sisso, bougainvillea, mint, devil’s cotton, drumstick, false daisy, asthma plant, and mimosa) were tested for their antibacterial effects against Xanthomonas campestris pv. campestris . The extracts were prepared in distilled water and ethanol at two concentrations, 25% and 50%. The extracts were applied, and a standard antibiotic disk (streptomycin 10 µg/disc) was used to evaluate the antibacterial activities. In the present study, antibacterial screening using the disk diffusion method revealed that both the aqueous and ethanol extracts of seven plant samples: royal poinciana, ivy gourd, sisso, bougainvillea, mint, devil cotton, and drumstick, showed significant activity, while extracts (aqueous and ethanol) of false daisy, asthma plant, and mimosa showed weak inhibitory effects against the tested bacteria. For both aqueous and ethanol extracts, antibacterial effects were higher at 50% concentration.