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Plant diseases caused by bacteria lead to enormous yield and economic losses in agricultural production. To develop innovative bactericides for controlling plant disease, a series of coumarin-3-carboxylic acid derivatives containing acylhydrazone thioether/sulfoxide were designed and synthesized by utilizing the principles of bioisosterism and active splicing. The bactericidal activities of these derivatives were subsequently evaluated. The result indicated that E2 exhibited the highest antibacterial activities in vitro against Xanthomonas oryzae pv. oryzae, Ralstonia solanacearum, and Acidovorax citrulli, with EC50 values of 2.97, 1.17, and 1.23 µg/mL, respectively. Moreover, in vivo experiments showed that E2 exhibited robust protective properties against Ralstonia solanacearum, and Acidovorax citrulli, with efficacies of 72.52 % and 63.90 %, respectively, at a concentration of 100 µg/mL, which was comparable to the positive control kasugamycin at the same concentration. Scanning electron microscopy analysis revealed that E2 induced changes in the cellular morphology of Acidovorax citrulli, such as shrinkage and collapse. Subsequent investigation revealed that E2 had the capacity to compromise the structural stability of the bacterial membrane of Ralstonia solanacearum. This study represents the first report on the antibacterial activities of this series of coumarin-3-carboxylic acid derivatives containing the acylhydrazone thioether/single-sulfoxide moiety, and the results suggest that coumarin-3-carboxylic acid derivatives containing the acylhydrazone single-sulfoxide may hold potential as effective antibacterial agents. And coumarin-3-carboxylic acid derivatives exhibited promise as plant bacterial agent to prevent rice bacterial leaf blight, tomato bacterial wilt, and melon bacterial fruit blotch.

Isolation for antibacterial compounds from natural plants is a promising approach to develop new pesticides. In this study, two compounds were obtained from the Chinese endemic plant Piper austrosinense using bioassay-guided fractionation. Based on analyses of 1H-NMR, 13C-NMR, and mass spectral data, the isolated compounds were identified as 4-allylbenzene-1,2-diol and (S)-4-allyl-5-(1-(3,4-dihydroxyphenyl)allyl)benzene-1,2-diol. 4-Allylbenzene-1,2-diol was shown to have strong antibacterial activity against four plant pathogens, including Xanthomonas oryzae pathovar oryzae (Xoo), X. axonopodis pv. citri (Xac), X. oryzae pv. oryzicola (Xoc) and X. campestris pv. mangiferaeindicae (Xcm). Further bioassay results exhibited that 4-allylbenzene-1,2-diol had a broad antibacterial spectrum, including Xoo, Xac, Xoc, Xcm, X. fragariae (Xf), X. campestris pv. campestris (Xcc), Pectobacterium carotovorum subspecies brasiliense (Pcb) and P. carotovorum subsp. carotovorum (Pcc), with minimum inhibitory concentration (MIC) values ranging from 333.75 to 1335 μmol/L. The pot experiment showed that 4-allylbenzene-1,2-diol exerted an excellent protective effect against Xoo, with a controlled efficacy reaching 72.73% at 4 MIC, which was superior to the positive control kasugamycin (53.03%) at 4 MIC. Further results demonstrated that the 4-allylbenzene-1,2-diol damaged the integrity of the cell membrane and increased cell membrane permeability. In addition, 4-allylbenzene-1,2-diol also prevented the pathogenicity-related biofilm formation in Xoo, thus limiting the movement of Xoo and reducing the production of extracellular polysaccharides (EPS) in Xoo. These findings suggest the value of 4-allylbenzene-1,2-diol and P. austrosinense could be as promising resources for developing novel antibacterial agents.

Corynespora blight, caused by Corynespora cassiicola (Berk. & M.A. Curtis) C.T. Wei, has become an important disease affecting cucumber in China. Its management mainly depends on fungicides; however, no research has been conducted to assess the sensitivity of C. cassiicola in China to boscalid. a succinate dehydrogenase inhibitor (SDHI). To facilitate boscalid resistance monitoring, baseline sensitivity was established. The EC50 value (i.e., the concentration that results in 50% mycelial growth inhibition) frequency distribution was unimodal with a right-hand tail; with the means 0.95 ± 0.51 µg/ml and the range 0.03 to 2.85 µml. We then assessed the sensitivity of C. cassiicola to boscalid using discriminatory doses and EC50 values. In total, 27.8% of the 798 isolates were resistant, distributed in five provinces and two municipalities. Thirty-seven isolates with different resistance levels to boscalid were also evaluated for their sensitivity to carboxin, tluopyram, and penthiopyrad. Seven SDHI resistance patterns were observed (i.e., 1: BosMR FluoMRPenLRCarSS; BosVHRFluoSSPenMRCarR; III: BosLRFluoMRPenLRCarR; IV: BosMRFluoMRPenMRCarR; V: BosHRFluoMRPenHRCarR; VI: BosHRFluoHRPenHRCarR; and VII: BosHRFluoSSPenLR CarR, VHR: very highly resistant; HR: highly resistant; MR: moderately resistant; LR: low resistant; R: resistant; SS: supersensitive), corresponding to seven mutations in sdhB/C/D genes, respectively. [ABSTRACT FROM AUTHOR]