Zhaoqian Fan,Yukun Qin,Song Liu,Ronge Xing,Huahua Yu,Kecheng Li,Pengcheng Li
The exploration of novel, environmentally friendly, and efficient nematicides is essential, and modifying natural biomacromolecules is one feasible approach. In this study, 6-O-(trifluorobutenyl-oxadiazol)-chitosan oligosaccharide derivative was synthesized and characterized by FTIR, NMR, and TG/DTG. Its bioactivity and action mode against root-knot nematodeM. incognitawere estimated. The results show that the derivative shows high nematicidal activity against J2s, and egg hatching inhibitory activity at 1 mg/mL. The derivative may affect nematode ROS metabolism and further damage intestinal tissue to kill nematode. Meanwhile, by synergism with improving crop resistance, the derivative performed a high control effect on the nematode with low phytotoxicity. These findings suggested that chitosan oligosaccharide derivatives bearing fluoroalkenyl groups are promising green nematicides.Keywords:chitosan oligosaccharide;nematicide;Meloidogyne incognita;trifluorobutenyl group
Background Root knot nematodes cause great damage to crops worldwide. Due to the negative effects of the application of fumigant and old chemical nematicides, biological nematicides have drawn increasing attention in recent years. Here we tested the fumigant activity of the volatile organic compounds (VOCs) blends emitted from Paenibacillus polymyxa and pure commercial VOCs against M. incognita . Results In this study, we investigated whether P. polymyxa strain J2-4 could produce VOCs that exhibit nematicidal activity. In vitro assays indicated that J2-4 VOCs were highly toxic to second stage juveniles (J2s) and could inhibit egg hatching. Three-layered pot experiments showed that the number of nematodes that penetrating in cucumber roots was reduced by 69.27% after the application of J2-4 VOCs under greenhouse conditions. We identified fourteen volatiles using solid-phase micro-extraction gas chromatography–mass spectrometry. The efficacy of six commercially available VOCs, namely 2-isobutyl-3-methylpyrazine, 2,4-dimethoxybenzaldoxime, 2-dodecanone, 2-tridecanol, 2-tridecanone, and 2-tetradecanol, against M. incognita were examined. Except for 2,4-dimethoxybenzaldoxime, the remaining five VOCs showed strong direct-contact nematicidal activity against J2s of M. incognita , and only 2-isobutyl-3-methylpyrazine showed strong fumigant activity against J2s of M. incognita . In pot experiments, 2-isobutyl-3-methylpyrazine and 2-dodecanone reduced the number of root galls by about 70%, and 2-tridecanone reduced the number of root galls and egg masses by about 63% compared with controls. Conclusion Paenibacillus polymyxa strain J2-4 exhibited high fumigant activity against M. incognita. Our results provide evidence for the use of J2-4 and its VOCs as biocontrol agents in the management of root-knot nematodes. This article is protected by copyright. All rights reserved.
Root-knot nematodes (RKNs, especially Meloidogyne incognita ) are a growing threat to greenhouse tomatoes in China. However, control methods in the greenhouses in China are limited. The use of chemical pesticides such as fluopyram and thiazole phosphate to control M. incognit a is expensive and harmful to the environment. The Chinese herb Asarum sieboldii is commonly used, and it shows potential as a plant-derived pesticide. We evaluated the effectiveness of A. sieboldii in regulating the soil nematode community and M. incognita in tomato greenhouses. Combining morphological identification with high-throughput sequencing techniques, we demonstrated that A. sieboldii root extract significantly reduced the relative abundance of plant-parasitic nematodes (PPNs) while promoting the ecological and functional recovery of bacterivorous (BF) and fungivorous (FF) nematodes. The aqueous extract exhibited high toxicity against M. incognita J2s and reduced the number of root galls by 69.5% per gram of root, decreased the number of egg masses by 58.4%, and enhanced shoot fresh weight by 53.6%. Through column chromatography and HPLC–MS analysis, mono-ethyl fumarate (MEF) and methyl gallate (MG) were identified as key active compounds, demonstrating LC50 values of 10.20 mg/L and 49.47 mg/L with root-knot suppression rates reaching 64.8% and 61.3% under greenhouse conditions. This study presents the first evidence that A. sieboldii aqueous extract effectively controls M. incognita without compromising the ecological balance of soil, providing a theoretical foundation for developing environmentally friendly botanical nematicides.
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