Plant extracts induce resistance in rice against bacterial blight disease by modulating antioxidant enzymes activity

Rice Bacterial Blight (BB), which is caused by Xanthomonas oryzae pv. oryzae (Xoo), is deemed as one of the most severe diseases that can afflict rice crops. Excessive use of synthetic bactericides to control this disease negatively impacts the surrounding environment. Plants have various metabolites that protect against phytopathogens. Thus, a promising and environment-friendly approach is needed for sustainable agriculture. Foliar application of natural products or compounds is one such strategy to enhance plant disease resistance. The study utilized plants with various pharmacological activities, including Argemone mexicana, Eucalyptus globulus, Bassia scoparia, Mallotus philippensis, and Shorea robusta, for various health benefits such as antibacterial, antiviral, dermatological, and wound healing property. Here, we demonstrate that foliar spray with the leaf extracts of different plants induces resistance in rice against X. oryzae pv. oryzae. Treatment with extracts significantly reduced the bacterial invasion from the 3rd to the 12th day of observation. Furthermore, higher chlorophyll A fluorescence in treated leaves indicates the photosystem's ІІ protection from Xoo damage. The resistance developed was evaluated by measuring the accumulation of antioxidant enzymes such as guaiacol peroxidase, catalase, superoxidase dismutase, glutathione reductase, and total protein content on the 3rd, 6th, and 9th day after treatment. Antioxidant enzymes and protein levels were higher in treated leaves than in the control, particularly on the 6th and 9th days after treatment. Malondialdehyde, an indicator of stress-related damage, was observed to be reduced in treated leaves on the 9th day. Additionally, the presence of phytochemicals that might help in triggering resistance was confirmed through an increased concentration of phenol, tannin, and flavonoids in the plant extract. Similar results were reflected in their antioxidant ability. Finally, Fourier transform-infrared spectroscopy (FT-IR) analysis confirms the presence of various functional groups, indicating distinct metabolites in the plant samples. Thus, the enhanced bacterial blight resistance in rice leaves treated with plant extracts can be attributed to the resistance-triggering effects. Further at large scale, plant extracts offer a sustainable alternative to synthetic bactericides due to their bioactive compounds, reducing environmental impact and chemical residues and promoting safer practices for humans and non-target organisms.