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Bacterial leaf blight (BLB) and sheath brown rot (SBR), caused by Xanthomonas oryzae pv. oryzae (Xoo) and Pseudomonas fuscovaginae, respectively, are bacterial diseases that lead to substantial yield losses in rice. Natural plant-based products represent a sustainable alternative to combat bacterial diseases due to their biodegradability and overall safety. However efficient ways of delivering them are crucial to their success. In an attempt to maximize the antibacterial properties of botanical bactericides for the control of these pathogens, this study evaluated the efficiency of different emulsion formulations of Piper sarmentosum extracts. The emulsion formulations were demonstrated to be effective in controlling BLB and SBR of rice in in vitro plate assays and in planta under glasshouse conditions. The observed in vitro inhibition of the bacterial pathogens and significant disease suppression in planta indicate that these plant extract formulations represent promising alternatives to be adopted in management strategies for controlling rice diseases., Agricultural science; Microbiology; Plant biology; Natural product chemistry; Bacterial leaf blight; Biological control; Sheath brown rot; Piper sarmentosum; Rice; Plant-based formulations.

Piper sarmentosum is a cultivated plant that also grows wildly in the South East Asian region. It is well known for its medicinal properties and a variety of active chemical constituents. The control potential of the plant extract against bacterial leaf blight caused by Xanthomonas oryzae and sheath brown rot of rice caused by Pseudomonas fuscovaginae was evaluated. The aqueous methanol extracts of fruits and leaves of P. sarmentosum were chemically analyzed using gas-chromatography mass-spectrometry (GC-MS). The results gave the highest best matches of 28 compounds (80.2% of total extracts) in the leaf extract and 24 compounds (89.1% of total extracts) in the fruit extract. The flavonoid fraction 4H-pyran-4-one,2,3-dihydro-3,5-dihydroxy-6-methyl- (DDMP) was found to be the major component which constitutes a complex natural product that has been of recent medicinal interest. The extract of the fruit had IC50 of 28.08 and 8.41 mg ml−1 against P. fuscovaginae and X. oryzae, respectively, while the leaf extract had IC50 of 10.42 and 24.69 mg ml−1 against P. fuscovaginae and X. oryzae, respectively.