Abstract
In this study, sulfone derivatives containing 1,3,4-oxadiazole moieties indicated good antibacterial activities against rice bacterial leaf blight caused by the pathogen Xanthomonas oryzaepv. pv. oryzae (Xoo). In particular, 2-(methylsulfonyl)-5-(4-fluorobenzyl)-1,3,4-oxadiazole revealed the best antibacterial activity against Xoo, with a half-maximal effective concentration (EC50) of 9.89 μg/mL, which was better than those of the commercial agents of bismerthiazole (92.61 μg/mL) and thiodiazole copper (121.82 μg/mL). In vivo antibacterial activity tests under greenhouse conditions and field trials demonstrated that 2-(methylsulfonyl)-5-(4-fluorophenyl)-1,3,4-oxadiazole was effective in reducing rice bacterial leaf blight. Meanwhile, 2-(methylsulfonyl)-5-(4-fluorophenyl)-1,3,4-oxadiazole stimulate the increase in superoxide dismutase (SOD) and peroxidase (POD) activities in rice, causing marked enhancement of plant resistance against rice bacterial leaf blight. It could also improve the chlorophyll content and restrain the increase in the malondialdehyde (MDA) content in rice to considerably reduce the amount of damage caused by Xoo. Moreover, 2-(methylsulfonyl)-5-(4-fluorophenyl)-1,3,4-oxadiazole, at a concentration of 20 μg/mL, could inhibit the production of extracellular polysaccharide (EPS) with an inhibition ratio of 94.52%, and reduce the gene expression levels of gumB, gumG, gumM, and xanA, with inhibition ratios of 94.88%, 68.14%, 86.76%, and 79.21%, respectively.
Highlights
Rice is one of the most important staple crops around the world
The expression of gumM was lowest at 20 μg/mL, with the inhibition rate of 86.76%, which suggested that compound 2-(methylsulfonyl)-5-(4-fluorophenyl)-1,3,4-oxadiazole may impeded the biosynthesis of the pentasaccharide of Xanthomonas oryzaepv. pv. oryzae (Xoo)
2-(methylsulfonyl)-5-(4-fluorophenyl)-1,3,4-oxadiazole could stimulate the increase in superoxide dismutase (SOD) and POD
Summary
Grain yield has decreased significantly because of rice bacterial leaf blight, which is caused by the pathogen. Bismerthiazole and streptomycin are the main tools for controlling rice bacterial leaf blight in China, Xoo has developed high resistance to both these bactericides [6,7]. We found that 1,3,4-oxadiazole-containg sulfone derivatives, which demonstrate potent antibacterial activities against R. solanacearum, were highly effective against rice bacterial leaf blight in vitro and in vivo. 2-(methylsulfonyl)-5-(4-fluorophenyl)-1,3,4-oxadiazole could stimulate an increase in superoxide dismutase (SOD) and peroxidase (POD) activities in rice, causing a marked enhancement of plant resistance against rice bacterial leaf blight. 2-(methylsulfonyl)-5-(4-fluorophenyl)-1,3,4-oxadiazole could obviously inhibit the production of extracellular polysaccharide (EPS) and reduce the gene expression levels of gumB, gumG, gumM, and xanA
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