Abstract
Bacterial leaf blight and blast diseases caused by the bacterium Xanthomonas oryzae pv. oryzae and the fungus Pyricularia oryzae, respectively, are among the most important infectious diseases affecting rice. We evaluated the antimicrobial effects of compounds derived from Praxelis clematidea on Xanthomonas oryzae and Pyricularia oryzae. The dried aerial parts of Praxelis clematidea were subjected to ethanol extraction, separated by solvent partitioning using hexane, chloroform, ethyl acetate, and water. In vitro assays demonstrated that the main antibacterial and antifungal activities were distributed in the ethyl acetate and chloroform fractions, respectively. These fractions were further separated using silica gel chromatography and reversed-phase chromatography. Finally, we isolated five compounds, 1–5, that inhibited the growth of Xanthomonas oryzae in vitro and four compounds, 6–9, that exhibited in vitro antifungal activity against Pyricularia oryzae. We evaluated their antimicrobial activities and identified their chemical structures by NMR and mass spectrometry analyses. This is the first study to isolate compound 2 (4,4′,4″-nitrilotriphenol) as an alternative microbial from natural resources and evaluate its physiological activity. Moreover, this is the first report to demonstrate antibacterial activity in comparison with flavonoids. Praxelis clematidea extracts plausibly exert both antibacterial and antifungal effects, which should be further validated in field trials.
Highlights
IntroductionVarious infectious diseases caused by fungi, bacteria, viruses, mycoplasma-like organisms, and nematodes affect rice [3,4,5]
Rice (Oryza sativa L.) is an essential cereal crop worldwide [1,2]
The chloroform fraction exhibited the highest anti-P. oryzae activity, which was expressed as the percent inhibition (PI) of the radial P. oryzae growth at 125 μg/mL (Figure 1B)
Summary
Various infectious diseases caused by fungi, bacteria, viruses, mycoplasma-like organisms, and nematodes affect rice [3,4,5]. Oryzae (Fang et al 1957) Swings et al.1990 (Xoo), the causative pathogen of leaf blight disease, and the fungus Pyricularia oryzae. Cavara 1892 (P. oryzae), the causative pathogen of rice blast disease, have widespread distribution and cause severe crop destruction in rice-growing regions globally [3,5,6]. Xoo can reduce the rice yield by approximately 50–70% under conditions favorable for the bacteria [5,7]. P. oryzae infects leaves, collars, nodes, internodes, necks, and other parts of the rice panicle and sometimes the leaf sheath [3,5,10]. Devising control strategies for these two pathogens is imperative
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