https://doi.org/10.37229/fsa.fja.2026.09.05

Crown gall disease, caused by Agrobacterium tumefaciens, is a destructive bacterial disease affecting numerous dicotyledonous crops and remains difficult to manage using conventional control strategies. Marine brown algae are rich in bioactive metabolites with antimicrobial properties and represent as promising source of environmentally sustainable disease management agents. This study evaluated the antibacterial activity of ethanol, water, and benzene extracts of Turbinaria ornata and Padina pavonica brown algae against A. tumefaciens 27AS_Pp4 (OK559740) under in vitro and in vivo conditions and quantified major phytochemical constituents. To our knowledge, limited information is available regarding the activity of T. ornata and P. pavonica extracts against A. tumefaciens. All extracts inhibited the growth of A. tumefaciens, with efficacy depending on both algal species and extraction solvent. The ethanolic extract of T. ornata showed the greatest antibacterial activity, producing the largest inhibition zone (25.7 ± 0.9 mm) at concentration 10 mg /ml, followed by the ethanolic extract of P. pavonica (22.3 ± 0.3 mm). Both ethanolic extracts showed the lowest minimum effective concentration (MEC) (0.0391 mg/ml). In tomato pot experiments, the ethanolic extract of T. ornata completely inhibited gall formation (100% disease reduction), whereas ethanolic extract of P. pavonica achieved 93.75% disease reduction, and T. ornata ethanol extract markedly improved tomato plant growth. Ethanolic extracts showed the highest contents of phenolics, flavonoids, tannins, saponins, and alkaloids. These findings indicate that solvent selection markedly influences the antibacterial activity of brown algal extracts. The ethanolic extract of T. ornata showing the greatest potential for sustainable crown gall management.