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BACKGROUND: Root knot nematodes (RKNs) pose a great threat to agricultural production worldwide. The bacterial nematocides have received increasing attention due to their safe and efficient control against RKNs. Here, we investigated the biocontrol efficacy of Paenibacillus polymyxa J2‐4 against Meloidogyne incognita in the field and analyzed the rhizosphere microbiome of cucumber under nematode infection after application of the J2‐4 strain. Furthermore, a biomarker strain of Pseudomonas spp. was isolated from the J2‐4‐inoculated rhizosphere soil, and its nematocidal activity and growth‐promoting effect on host plants were determined. In addition, chemotaxis assay of P. fluroescens ZJ5 toward root exudates was carried out. RESULTS: The field experiment demonstrated that P. polymyxa J2‐4 could effectively suppressed gall formation in cucumber plants, with the galling index reduced by 67.63% in 2022 and 65.50% in 2023, respectively, compared with controls. Meanwhile, plant height and yield were significantly increased in J2‐4 treated plants compared with controls. Metagenomic analysis indicated that J2‐4 altered the rhizosphere microbial communities. The relative abundance of Pseudomonas spp. was notably enhanced in the J2‐4 group, which was consistent with Linear discriminant analysis Effect Size results that Pseudomonas was determined as one of the biomarkers in the J2‐4 group. Furthermore, the ZJ5 strain, one of the biomarker Pseudomonas strains, was isolated from the J2‐4‐inoculated rhizosphere soil and was identified as Pseudomonas fluorescens. In addition, P. fluorescens ZJ5 exhibited high nematicidal activity in vitro and in vivo, with 99.20% of the mortality rate of M. incognita at 24 h and 69.75% of gall index reduction. The biocontrol efficiency of the synthetic community of ZJ5 plus J2‐4 was superior to that of any other single bacteria against M. incognita. Additionally, ZJ5 exhibited great chemotaxis ability toward root exudates inoculated with J2‐4. CONCLUSION: Paenibacillus polymyxa J2‐4 has good potential in the biological control against M. incognita under field conditions. Enrichment of the beneficial bacteria Pseudomonas fluorescens ZJ5 in the J2‐4‐inoculated rhizosphere soil contributes to M. incognita management. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

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 14 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. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND All previously and currently used methods for effectiveness evaluation of control measures for the diamondback moth ( DBM) do not simultaneously take the actual damage and population size into consideration. Here, we propose a new method, the cumulative damage index method, in which the number of larvae and their amount of food consumption are simultaneously included in the calculation of the theoretical cumulative damage index ( T) and actual cumulative damage index ( A). Evaluation was based on the reduced degree of damage calculated according to indexes T and A. RESULTS Based on the new method, the corrected effectiveness of the combined use of biological measures, chemical insecticides, Bacillus thuringiensis ( Bt) and P. xylostella granulosis virus ( PxGV) on DBM was 35.85, 2.37, 12.50 and 11.77% respectively. Under the action of natural factors, the Population Developmental Index ( I) of DBM was 5.1 ± 1.4; under the integrated actions of natural factors and these four types of measure, index I of DBM was 0.34 ± 0.1, 6.1 ± 1.5, 2.1 ± 0.5 and 1.1 ± 0.3 respectively. The sole effectiveness of Trichogramma spp. when integrated with other natural factors, integrated biological measures and chemical insecticides was 21.43 ± 1.69%, 45.27 ± 4.09% and 20.68 ± 2.60% respectively. CONCLUSIONS There was some difference between the effectiveness evaluated by the new method and index I, and the actual damage caused by DBM could be reflected well by index A. The new method is more scientifically appropriate and practical for effectiveness evaluation than existing methods. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Meloidogyne incognita is one of the most destructive agricultural pathogens around the world, resulting in severe damage to yield and quality in agricultural production. Biological control promises to be a great potential alternative to chemical agents against M. incognita. Paenibacillus polymyxa J2-4, isolated from ginger plants injured by M. incognita , has shown excellent biocontrol efficacy against M. incognita in cucumber. In vitro experiments with the strain J2-4 resulted in a correct mortality rate of 88.79% (24 h) and 98.57% (48 h) for second-stage juveniles (J2s) of M. incognita. Strain J2-4 significantly suppressed nematode infection on potted plants, with a 65.94% reduction in galls and a 51.64% reduction in eggs compared with the control. The split-root assay demonstrated that strain J2-4 not only reduced J2s' invasion but also inhibited nematode development through the dependence on salicylic acid and jasmonic acid signaling of strain J2-4 induction of plant resistance in local and systemic roots of cucumbers. Genomic analysis of strain J2-4 indicated biosynthetic gene clusters encoding polymyxin, fusaricidin B, paenilan, and tridecaptin. In addition, genetic analysis showed that none of the genes encoding virulence factors were detected in the genome of J2-4 compared with the pathogenic Bacillus species. Taking all the data together, we conclude that P. polymyxa J2-4 has potential as a biological control agent against M. incognita on cucumbers and can be considered biologically safe when used in agriculture., Competing Interests: The author(s) declare no conflict of interest.

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 14 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. © 2023 Society of Chemical Industry., (© 2023 Society of Chemical Industry.)