Antibacterial Activity of Plant Extracts against Xanthomonas oryzae pv. oryzae Causing Bacterial Leaf Blight in Rice

Abstract

Bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), is an important rice disease that can reduce crop productivity under favourable conditions. This study evaluated the antibacterial activity of selected aqueous plant extracts against Xoo under in vitro conditions. Eight plant extracts, namely neem, tulasi, garlic, turmeric, calotropis, kanuga, aloe vera and mint, were prepared using sterile distilled water and tested at 5%, 10% and 20% concentrations by the disc diffusion method. The experiment was arranged in a factorial completely randomised design with three replications. Significant variation was observed among the extracts and concentrations. Inhibition of bacterial growth increased as extract concentration increased. Among the tested botanicals, tulasi extract produced the highest inhibition zones of 37.0, 55.7 and 62.7 mm at 5%, 10% and 20%, respectively, with an overall mean inhibition of 51.8 mm. Calotropis and aloe vera extracts were the next most effective treatments, with mean inhibition zones of 40.9 and 39.7 mm, respectively. Kanuga, neem, turmeric, garlic and mint showed comparatively lower to moderate antibacterial activity. Garlic and mint did not inhibit bacterial growth at 5% but showed inhibition at higher concentrations. The untreated control showed no inhibition. These findings indicate that selected plant extracts, particularly tulasi, calotropis and aloe vera, possess inhibitory activity against Xoo under laboratory conditions. Further greenhouse and field studies are required to validate their effectiveness and standardise suitable formulations and application methods for bacterial leaf blight management in rice.