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.