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Plant parasitic nematodes cause significant crop damage globally. Currently, many nematicides have been banned or are being phased out in Europe and other parts of the world because of environmental and human health concerns. Therefore, we need to focus on sustainable and alternative methods of nematode control to protect crops. Plant roots contain and release a wide range of bioactive secondary metabolites, many of which are known defense compounds. Hence, profound understanding of the root mediated interactions between plants and plant parasitic nematodes may contribute to efficient control and management of pest nematodes. In this review, we have compiled literature that documents effects of root metabolites on plant parasitic nematodes. These chemical compounds act as either nematode attractants, repellents, hatching stimulants or inhibitors. We have summarized the few studies that describe how root metabolites regulate the expression of nematode genes. As non-herbivorous nematodes contribute to decomposition, nutrient mineralization, microbial community structuring and control of herbivorous insect larvae, we also review the impact of plant metabolites on these non-target organisms.

The Meloidogyne genus is widely recognized for its significant economic and scientific importance within the group of plant-parasitic nematodes. The chemical management of nematodes presents its challenges and heavily depends on employing soil fumigants containing toxic and costly nematicides. However, plant-derived essential oils offer promising alternatives, demonstrating a wide range of biological activities that affect nematodes through a range of mechanisms, including disrupting their nervous systems, inducing detrimental effects on plasma membrane permeability, penetrating the gelatinous matrix of nematode eggs, and disturbing intracellular redox status. Most of the extracted essential oils were predominantly sourced from the Lamiaceae family (32%), followed by Asteraceae (11%), Apiaceae (9%), and Poaceae (8%), and with genera Thymus, Mentha, Ocimum, Artemisia, Cymbopogon being the most common. The nematicidal activity of EOs primarily arises from their chemical groups, such as terpenes, phenylpropanoids, and organosulfur compounds. Among these, geraniol, carvacrol, limonene, eugenol, thymol, and pinene demonstrate the strongest nematicidal potential. The assessed EO efficacy was evaluated against 6 species belonging to the genus Meloidogyne. This review also provides knowledge of synergistic and antagonistic interactions of EO components. Synergistic interactions were identified between carvacrol and geraniol, as well as geraniol and eugenol, whereas binary combinations of carvacrol, γ-terpinene, and o-cymene exhibited reduced efficacy. Understanding how specific compounds interact can lead to the development of more potent and effective final products.

Plant-parasitic nematodes (PPNs) infect and cause substantial yield losses of many foods, feed, and fiber crops. Increasing concern over chemical nematicides has increased interest in safe alternative methods to minimize these losses. This review focuses on the use and potential of current methods such as biologicals, botanicals, non-host crops, and related rotations, as well as modern techniques against PPNs in sustainable agroecosystems. To evaluate their potential for control, this review offers overviews of their interactions with other biotic and abiotic factors from the standpoint of PPN management. The positive or negative roles of specific production practices are assessed in the context of integrated pest management. Examples are given to reinforce PPN control and increase crop yields via dual-purpose, sequential, and co-application of agricultural inputs. The involved PPN control mechanisms were reviewed with suggestions to optimize their gains. Using the biologicals would preferably be backed by agricultural conservation practices to face issues related to their reliability, inconsistency, and slow activity against PPNs. These practices may comprise offering supplementary resources, such as adequate organic matter, enhancing their habitat quality via specific soil amendments, and reducing or avoiding negative influences of pesticides. Soil microbiome and planted genotypes should be manipulated in specific nematode-suppressive soils to conserve native biologicals that serve to control PPNs. Culture-dependent techniques may be expanded to use promising microbial groups of the suppressive soils to recycle in their host populations. Other modern techniques for PPN control are discussed to maximize their efficient use.

Purpureocillium lilacinum is a biocontrol Ascomycota fungus against various plant pathogens. In the present study, the efficacy of P . lilacinum was evaluated against a root-knot nematode, Meloidogyne incognita that infects eggplants. We performed an in vitro experiment in which the direct effects of P . lilacinum on the second-stage juvenile survival and egg hatching of M . incognita were tested at different exposure times. The results showed that P . lilacinum significantly reduced the rates of egg hatching and juvenile survival in a dose-dependent manner. Microscopic observation demonstrated that P . lilacinum directly penetrated the eggs and contacted the juveniles, indicating how P . lilacinum parasitizes M . incognita . We also performed a pot assay in which soil-grown eggplants were treated with P . lilacinum followed by inoculation with M . incognita . The results indicated that P . lilacinum effectively reduced the nematode population and the number of galls in plant roots. Interestingly, application of P . lilacinum resulted in significant enhancements in plant growth and biomass, even under nematode infection, while it improved plant photosynthetic pigments, i.e., chlorophyll and carotenoids. Taken together, our study suggested that P . lilacinum can be used as a plant growth-promoting fungus and a biological nematicide for disease management of root-knot nematodes in eggplants.

This study sought to identify and characterize Heterorhabditis indica, its symbiotic bacteria, and Meloidogyne incognita, while assessing the nematicidal efficacy of silver nanoparticles synthesized using Photorhabdus luminescens supernatant (PsAgNPs). Molecular and phylogenetic analyses verified the identity of H. indica and M. incognita, revealing no nucleotide discrepancies from previously characterized species. P. luminescens exhibited entomopathogenic properties, and its supernatant enabled the biosynthesis of PsAgNPs under optimal conditions (26 ± 2°C, pH 9). Characterization of PsAgNPs indicated a UV–visible absorption peak at 430 nm, a crystalline structure with an average particle size of 22.38 nm (XRD), and a zeta potential of -41.7 ± 0.74 mV, signifying high stability. FTIR analysis suggested that proteins and polysaccharides contributed to nanoparticle stabilization, while EDX confirmed 70.01% silver purity. SEM and TEM analyses demonstrated spherical nanoparticles with sizes ranging from 15.5 to 40 nm. In vitro bioassays revealed that PsAgNPs significantly suppressed M. incognita egg hatchability and juvenile mortality in a dose-dependent manner. At 200 µg/mL, PsAgNPs reduced egg hatchability to 24.6% and caused 100% juvenile mortality. In contrast, the bacterial supernatant alone exhibited a lower efficacy. The LC50 values for PsAgNPs were 13.1 µg/mL and 14 µg/mL at 12 and 24 h, respectively, indicating potent nematicidal activity. In vivo pot experiments on tomato plants demonstrated a pronounced reduction in gall formation (95.3%) and egg mass production (93.1%) at 100 µg/mL PsAgNPs. Soil nematode populations were significantly reduced, with the lowest density recorded in PsAgNP-treated plants (53.3 juveniles). Additionally, PsAgNPs substantially enhanced plant growth, increasing fresh and dry shoot and root biomass by 61.2% and 64.6%, respectively, compared to controls. Histopathological analysis corroborated reduced tissue damage in PsAgNP-treated plants. These results underscore the potential of PsAgNPs as a viable biocontrol agent for managing M. incognita, presenting an environmentally sustainable alternative to traditional nematicides.

Burkholderia vietnamiensis B418 is a multifunctional plant growth-promoting rhizobacteria (PGPR) strain with nitrogen-fixing and phosphate-solubilizing capability which can be employed for root-knot nematode (RKN) management on various crops and vegetables. Here we investigated the control efficacy of B. vietnamiensis B418 inoculation against RKN on watermelon, applied either alone or combined with nematicides fosthiazate or avermectin, and their effects on bacterial and fungal microbiomes in rhizosphere soil. The results of field experiments showed individual application of B418 displayed the highest control efficacy against RKN by 71.15%. The combinations with fosthiazate and avermectin exhibited slight incompatibility with lower inhibitory effects of 62.71% and 67.87%, respectively, which were still notably higher than these nematicides applied separately. Analysis of microbiome assemblages revealed B418 inoculation resulted in a slight reduction for bacterial community and a significant increment for fungal community, suggesting that B418 could compete with other bacteria and stimulate fungal diversity in rhizosphere. The relative abundance of Xanthomonadales, Gemmatimonadales and Sphingomonadales increased while that of Actinomycetales reduced with B418 inoculation. The predominate Sordariomycetes of fungal community decreased dramatically in control treatment with B418 inoculation whereas there were increments in fosthiazate and avermectin treatments. Additionally, nitrogen (N) cycling by soil microbes was estimated by quantifying the abundance of microbial functional genes involved in N-transformation processes as B418 has the capability of N-fixation. The copy number of N-fixing gene nifH increased with B418 inoculation, and the highest increment reached 35.66% in control treatment. Our results demonstrate that B. vietnamiensis B418 is an effective biological nematicide for nematode management, which acts through the modulation of rhizosphere microbial community.

Parasitic nematodes are a major threat to global food security, particularly as the world amasses 10 billion people amid limited arable land 1 – 4 . Most traditional nematicides have been banned owing to poor nematode selectivity, leaving farmers with inadequate means of pest control 4 – 12 . Here we use the model nematode Caenorhabditis elegans to identify a family of selective imidazothiazole nematicides, called selectivins, that undergo cytochrome-p450-mediated bioactivation in nematodes. At low parts-per-million concentrations, selectivins perform comparably well with commercial nematicides to control root infection by Meloidogyne incognita , a highly destructive plant-parasitic nematode. Tests against numerous phylogenetically diverse non-target systems demonstrate that selectivins are more nematode-selective than most marketed nematicides. Selectivins are first-in-class bioactivated nematode controls that provide efficacy and nematode selectivity. A metabolically bioactivated selective imidazothiazole nematicide shows comparable effectiveness at controlling plant root infection by Meloidogyne incognita to commercial nematicides, which are traditionally nonselective and toxic.

Plant root-knot nematode disease is a great agricultural problem and commercially available nematicides have the disadvantages of high toxicity and limited usage; thus, it is urgent to develop new nematicides derived from nature substances. In this study, a novel fluorinated derivative was synthesized by modifying chitosan oligosaccharide (COS) using the strategy of multiple functions. The derivatives were characterized by FTIR, NMR, elemental analysis, and TG/DTG. The activity assays show that the derivatives can effectively kill the second instar larvae of Meloidogyne incognita in vitro, among them, chitosan-thiadiazole-trifluorobutene (COSSZFB) perform high eggs hatching inhibitory activity. The derivatives can regulate plant growth (photosynthetic pigment), improve immunity (chitinase and β-1,3-glucanase), and show low cytotoxicity and phytotoxicity. According to the multi-functional activity, the derivatives exhibit a good control effect on plant root-knot nematode disease in vivo. The results demonstrate that the COS derivatives (especially fluorinated derivative) perform multiple activities and show the potential to be further evaluated as nematicides.

The primary strategy for managing Nacobbus aberrans has traditionally relied on synthetic chemicals. However, increasing regulatory pressure on unsafe products has led to a growing research focus on nematicides. Despite this, chemical nematicides remain more effective than other control methods. Consequently, there is a pressing need to develop novel nematicides that are both effective and environmentally safer. This study aimed to evaluate the nematocidal efficacy of various synthetic molecules against the second-stage juveniles of N. aberrans, the false root-knot nematode. A total of fifty-eight synthetic derivatives were obtained and tested in vitro at a concentration of 500 µg/mL. The results identified the AGAz family as the most promising, with AGAz-3 (LC50: 52.7 µg/mL) and AGAz-4 (LC50: 103.22 µg/mL) surpassing the efficacy of chitosan. Our findings emphasize the strong potential of AGAz-3 and AGAz-4 as nematocidal agents, particularly for in situ applications in agricultural settings. Additionally, AGAz-3 demonstrates potential not only as a nematocidal agent but also as an incentive for related research exploring its analogs as effective ovicidal compounds and investigating its efficacy against other phytonematodes. Furthermore, compounds from the N-Sulfonyl-hydrazone and N-acyl-hydrazone series showed efficacy (>50%), warranting additional experiments to assess their effectiveness across the most important pest phytonematodes.

IntroductionPine wilt disease (PWD) is responsible for extensive economic and ecological damage to Pinus spp. forests and plantations worldwide. PWD is caused by the pine wood nematode (PWN, Bursaphelenchus xylophilus ) and transmitted into pine trees by a vector insect, the Japanese pine sawyer (JPS, Monochamus alternatus ). Host infection by PWN will attract JPS to spawn, which leads to the co-existence of PWN and JPS within the host tree, an essential precondition for PWD outbreaks. Through the action of their metabolites, microbes can manipulate the co-existence of PWN and JPS, but our understanding on how key microorganisms engage in this process remains limited, which severely hinders the exploration and utilization of promising microbial resources in the prevention and control of PWD.MethodsIn this study we investigated how the PWN-associated fungus Aspergillus promotes the co-existence of PWN and JPS in the host trees ( Pinus massoniana ) via its secondary metabolite, sterigmatocystin (ST), by taking a multi-omics approach (phenomics, transcriptomics, microbiome, and metabolomics).ResultsWe found that Aspergillus was able to promote PWN invasion and pathogenicity by increasing ST biosynthesis in the host plant, mainly by suppressing the accumulation of ROS (reactive oxygen species) in plant tissues that could counter PWN. Further, ST accumulation triggered the biosynthesis of VOC (volatile organic compounds) that attracts JPS and drives the coexistence of PWN and JPS in the host plant, thereby encouraging the local transmission of PWD. Meanwhile, we show that application of an Aspergillus inhibitor (chiricanine A treatment) results in the absence of Aspergillus and decreases the in vivo ST amount, thereby sharply restricting the PWN development in host. This further proved that Aspergillus is vital and sufficient for promoting PWD transmission.DiscussionAltogether, these results document, for the first time, how the function of Aspergillus and its metabolite ST is involved in the entire PWD transmission chain, in addition to providing a novel and long-term effective nematicide for better PWD control in the field.