Phytochemical and Antibacterial Efficacy of Medicinal Plant Extracts against Xanthomonas oryzae pv. oryzae

Rice is one of the most extensively cultivated and economically significant crops worldwide. However, bacterial blight, is caused by Xanthomonas oryzae pv. oryzae, poses a significant threat, leading to considerable yield losses. The rising challenge of antibiotic resistance among bacterial pathogens in plant, including Xanthomonas oryzae pv. oryzae, underscores the need to explore sustainable alternatives to synthetic chemicals. This study investigates the phytochemical composition and antibacterial activity of leaf extracts from six medicinal plants: Azadirachta indica, Melia azedarach, Pongamia glabra, Lawsonia inermis, Mentha piperita, and Ocimum basilicum. Phytochemical analysis revealed the presence of bioactive compounds such as flavonoids, terpenoids, tannins, cardiac glycosides, phenols, and saponins in varying combinations. The antibacterial activity was evaluated using the well-diffusion method at 10 per cent and 20 per cent concentrations. Among the aqueous extracts, Pongamia glabra demonstrated the highest antibacterial potential, with a zone of inhibition (ZOI) of 11.83 ± 0.10 mm at 20 per cent concentration, corresponding to a relative per cent inhibition (RPI) of 73.96 per cent and an activity index (AI) of 0.74. Melia azedarach followed, exhibiting a ZOI of 10.25 ± 0.22 mm (RPI = 64.06%, AI = 0.64). Similar trends were observed with methanolic extracts, where Pongamia glabra and Melia azedarach showed the strongest activity. The positive control (Streptocycline, 100 ppm) produced a ZOI of 16.00 ± 0.45 mm, validating the experimental setup, while the negative control Dimethyl salphoxide (DMSO) showed no inhibitory effect. The results highlight the potential of locally available medicinal plants, particularly Pongamia glabra and Melia azedarach, as eco-friendly anti-microbial agents against Xanthomonas oryzae pv. oryzae.