Suppression of root-knot nematode Meloidogyne incognita on tomato plants using the nematode trapping fungus Arthrobotrys oligospora Fresenius

Nematode-trapping fungus Arthrobotrys oligospora recruited rhizosphere microorganisms to cooperate in controlling root-knot nematodes in tomato

AIMS

The objective of this study was to elucidate the role and mechanism of changes in the rhizosphere microbiome following Arthrobotrys oligospora treatment in the biological control of root-knot nematodes and identify the key fungal and bacterial species that collaborate with A. oligospora to biocontrol root-knot nematodes.

METHODS AND RESULTS

We conducted a pot experiment to investigate the impact of A. oligospora treatment on the biocontrol efficiency of A. oligospora against Meloidogyne incognita infecting tomatoes. We analyzed the rhizosphere bacteria and fungi communities of tomato by high-throughput sequencing of the 16S rRNA gene fragment and the internal transcribed spacer (ITS). The results indicated that the application of A. oligospora resulted in a 53.6% reduction in the disease index of M. incognita infecting tomato plants. The bacterial diversity of rhizosphere soil declined in the A. oligospora-treated group, while fungal diversity increased. The A. oligospora treatment enriched the tomato rhizosphere with Acidobacteriota, Firmicutes, Bradyrhizobium, Sphingomonadales, Glomeromycota, and Purpureocillium. These organisms are involved in the utilization of rhizosphere organic matter, nitrogen, and glycerolipids, or play the role of ectomycorrhiza or directly kill nematodes. The networks of bacterial and fungal co-occurrence exhibited a greater degree of stability and complexity in the A. oligospora treatment group.

CONCLUSIONS

This study demonstrated the key fungal and bacterial species that collaborate with the A. oligospora in controlling the root-knot nematode and elaborated the potential mechanisms involved. The findings offer valuable insights and inspiration for the advancement of bionematicide based on nematode-trapping fungi.

Biocontrol of plant parasitic nematodes by bacteria and fungi: a multi-omics approach for the exploration of novel nematicides in sustainable agriculture

Plant parasitic nematodes (PPNs) pose a significant threat to global crop productivity, causing an estimated annual loss of US $157 billion in the agriculture industry. While synthetic chemical nematicides can effectively control PPNs, their overuse has detrimental effects on human health and the environment. Biocontrol agents (BCAs), such as bacteria and fungi in the rhizosphere, are safe and promising alternatives for PPNs control. These BCAs interact with plant roots and produce extracellular enzymes, secondary metabolites, toxins, and volatile organic compounds (VOCs) to suppress nematodes. Plant root exudates also play a crucial role in attracting beneficial microbes toward infested roots. The complex interaction between plants and microbes in the rhizosphere against PPNs is mostly untapped which opens new avenues for discovering novel nematicides through multi-omics techniques. Advanced omics approaches, including metagenomics, transcriptomics, proteomics, and metabolomics, have led to the discovery of nematicidal compounds. This review summarizes the status of bacterial and fungal biocontrol strategies and their mechanisms for PPNs control. The importance of omics-based approaches for the exploration of novel nematicides and future directions in the biocontrol of PPNs are also addressed. The review highlighted the potential significance of multi-omics techniques in biocontrol of PPNs to ensure sustainable agriculture.

Multilocus Phylogeny and Characterization of Five Undescribed Aquatic Carnivorous Fungi (Orbiliomycetes)

The diversity of nematode-trapping fungi (NTF) holds significant theoretical and practical implications in the study of adaptive evolution and the bio-control of harmful nematodes. However, compared to terrestrial ecosystems, research on aquatic NTF is still in its early stages. During a survey of NTF in six watersheds in Yunnan Province, China, we isolated 10 taxa from freshwater sediment. Subsequent identification based on morphological and multigene (ITS, TEF1-α, and RPB2) phylogenetic analyses inferred they belong to five new species within Arthrobotrys. This paper provides a detailed description of these five novel species (Arthrobotrys cibiensis, A. heihuiensis, A. jinshaensis, A. yangbiensis, and A. yangjiangensis), contributing novel insights for further research into the diversity of NTF and providing new material for the biological control of aquatic harmful nematodes. Additionally, future research directions concerning aquatic NTF are also discussed.

Cellular communication and fusion regulate cell fusion, trap morphogenesis, conidiation, and secondary metabolism in Arthrobotrys oligospora

Signal-mediated cell fusion is vital for colony development in filamentous fungi. Arthrobotrys oligospora is a representative nematode-trapping (NT) fungus that produces adhesive networks (traps) to capture nematodes. Here, we characterized Aoadv-1, Aoso, Aoham-6, and Aoham-5 of A. oligospora, homologs of proteins involved in cellular communication and fusion in the model fungus Neurospora crassa. The deletion of four genes resulted in the complete loss of cell fusion, and traps produced by mutants did not close to form mycelial rings but were still capable of capturing nematodes. The absence of these genes inhibits aerial mycelial extension, slows colony growth, and increases mycelial branching. In addition, the mutants showed reduced sporulation capacity and tolerance to oxidative stress, increased sensitivity to SDS, and disturbed lipid droplet accumulation and autophagy. In addition, transcriptome and metabolomic analyses suggested that Aoadv-1 and Aoso are involved in multiple cellular processes and secondary metabolism. Our results revealed that Aoadv-1, Aoso, Aoham-6, and Aoham-5 regulate mycelial growth and trap morphogenesis through cell fusion, which contributed to elucidating the molecular mechanisms of cellular communication regulating mycelial development and trap morphogenesis in NT fungi.

Siderophore-synthesizing NRPS reprogram lipid metabolic profiles for phenotype and function changes of Arthrobotrys oligospora

The objective of this paper is to explore the function of the AOL-s00215g415 (Aog415) gene, which encodes for the synthesis of siderophore in the nematode trapping fungal model strain A. oligospora, in order to understand the relationship between siderophore biosynthesis and nematode trapping activity. After a through sequence analysis, it was determined that Aog415 is a siderophore-synthesizing NRPS. The product of this gene was then identified to be the hydroxamate siderophore desferriferrichrome, using mass spectrometry analysis. When compared to the WT strains, the Aog415 knockout strain exhibited a 60% decrease in siderophore content in fermentation broth. Additionally, the number of predatory rings of decreased by 23.21%, while the spore yield increased by 37.34%. The deletion of Aog415 did not affect the growth of A. oligospora in diverse nutrient medium. Lipid metabolism-related pathways were the primary targets of Aog415 disruption as revealed by the metabolomic analysis. In comparison to the WT, a significant reduction in the levels of glycerophospholipids, and glycolipids was observed in the mutation. The metabolic alteration in fatty acyls and amino acid-like molecules were significantly disrupted. The knockout of Aog415 impaired the biosynthesis of the hydroxamate siderophore desferriferrichrome, remodeled the flow of fatty acid in A. oligospora, and mainly reprogrammed the membrane lipid metabolism in cells. Desferriferrichrome, a hydroxamate siderophore affects the growth, metabolism and nematode trapping ability of A. oligospora by regulating iron intake and cell membrane homeostasis. Our study uncovered the significant contribution of siderophores to the growth and nematode trapping ability and constructed the relationship among siderophores biosynthesis, lipid metabolism and nematode trapping activity of A. oligospora, which provides a new insight for the development of nematode biocontrol agents based on nematode trapping fungi.

Analysis of Nuclear Dynamics in Nematode-Trapping Fungi Based on Fluorescent Protein Labeling

Nematophagous fungi constitute a category of fungi that exhibit parasitic behavior by capturing, colonizing, and poisoning nematodes, which are critical factors in controlling nematode populations in nature, and provide important research materials for biological control. Arthrobotrys oligospora serves as a model strain among nematophagous fungi, which begins its life as conidia, and then its hyphae produce traps to capture nematodes, completing its lifestyle switch from saprophytic to parasitic. There have been many descriptions of the morphological characteristics of A. oligospora lifestyle changes, but there have been no reports on the nuclear dynamics in this species. In this work, we constructed A. oligospora strains labeled with histone H2B-EGFP and observed the nuclear dynamics from conidia germination and hyphal extension to trap formation. We conducted real-time imaging observations on live cells of germinating and extending hyphae and found that the nucleus was located near the tip. It is interesting that the migration rate of this type of cell nucleus is very fast, and we speculate that this may be related to the morphological changes involved in the transformation to a predatory lifestyle. We suggest that alterations in nuclear shape and fixation imply the immediate disruption of the interaction with cytoskeletal mechanisms during nuclear migration. In conclusion, these findings suggest that the signal initiating nuclear migration into fungal traps is generated at the onset of nucleus entry into a trap cell. Our work provides a reference for analysis of the dynamics of nucleus distribution and a means to visualize protein localization and interactions in A. oligospora.

Isolation, Identification, and Evaluation of the Predatory Activity of Chinese Arthrobotrys Species towards Economically Important Plant-Parasitic Nematodes

The current investigation aimed to isolate and identify predatory fungal strains and evaluate their efficacy in mitigating the effects of plant-parasitic nematodes. We successfully isolated three distinct nematophagous fungal strains from soil samples, identified as Arthrobotrys megalosporus, A. oligospora, and A. sinensis, using conventional and molecular identification methodologies. In vitro trials illustrated the high capture efficiency of these fungi against plant-parasitic nematodes. Over an exposure period of 48 h to Aphelenchoides besseyi, Bursaphelenchus xylophilus, and Ditylenchus destructor, A. megalosporus (GUCC220044) displayed predation rates of 99.7%, 83.0%, and 21.1%, respectively. A. oligospora (GUCC220045) demonstrated predation rates of 97.3%, 97.3%, and 54.6%, and A. sinensis (GUCC220046) showed rates of 85.1%, 68.3%, and 19.0% against the same cohort of nematodes. The experimental outcomes substantiate that all three identified fungal strains demonstrate predatory activity against the tested nematodes, albeit with varying efficiencies.

Counter-attack of biocontrol agents: Environmentally benign Approaches against Root-knot nematodes (Meloidogyne spp.) on Agricultural crops

Root-knot nematodes (Meloidogyne spp.) are obligate sedentary endoparasites, considered severe crop-damaging taxa among all plant-parasitic nematodes globally. Their attacks through parasitic proteins alter the physiology and machinery of the host cells to favour parasitism and reduction in crop yield. Currently, the use of excessive pesticides as a fast remedy to manage this pest is hazardous for both the environment and humans. Keeping this view in mind, there is an urgent need for developing efficient eco-friendly strategies. Bio-control as an eco-friendly is considered the best approach to manage nematodes without disturbing non-target microbes. In bio-control, living agents such as fungi and bacteria are the natural enemies of nematodes and the best substitute for pesticides. Fungi, including nematode-trapping fungi, can sense host signals and produce special trapping devices viz., constricting rings and adhesive knobs/loops, to capture nematodes and kill them. Whereas, endo-parasitic fungi kill nematodes by enzymatic secretions and spore adhesion through their hyphae. Bacteria can also control nematodes by producing antibiotic compounds, competing for nutrients and rhizosphere, production of hydrolytic enzymes viz., chitinases, proteases, lipases, and induction of systemic resistance (ISR) in host plants. Scientists throughout the world are trying to evolve environmentally benign methods that sustain agricultural production and keep nematodes below a threshold level. Whatever methods evolve, in the future the focus should be on important aspects like green approaches for managing nematodes without disturbing human health and the environment.

Primary Screening of Microorganisms against Meloidogyne hapla (Chitwood, 1949) under the Conditions of Laboratory and Vegetative Tests on Tomato

Highly adapted obligate endoparasites of the root system, root-knot nematodes (Meloidogyne spp.), cause great damage to agricultural crops. Our research is aimed at the assessment of nematicidal activity and effectiveness of antagonist fungal and bacterial strains against the most common type of root-knot nematode in the south of Russia. By means of molecular genetic identification, it was found that in the south of Russia, the species Meloidogyne hapla Chitwood, 1949 and Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949 cause galls on the roots of open-ground and greenhouse tomato. Screening of microbial agents against second-stage juvenile (J2) M. hapla was carried out in the laboratory. At the end of the experiment, two liquid fungal cultures of Paecilomyces lilacinus BK-6 and Metarhizium anisopliae BK-2 were isolated, the nematicidal activity of which reached 100.0 and 70.2%, and exceeded the values of the biological standard (Nemotafagin-Mikopro) by 38.4% and 8.8%. The highest biological efficacy was noted in the liquid cultures of P. lilacinus BK-6, M. anisopliae BK-2, and Arthrobotrys conoides BK-8 when introduced into the soil before planting tomato. The number of formed galls on the roots was lower in comparison with the control by 81.0%, 75.5%, and 74.4%.

Ammonia and Nematode Ascaroside Are Synergistic in Trap Formation in Arthrobotrys oligospora

Nematode-trapping (NT) fungi are natural predators of the soil living nematodes. Diverse external signals mediate the generation of predatory devices of NT fungi. Among these, broad ascarosides and nitrogenous ammonia are highly efficient inducers for trap structure initiation. However, the overlay effect of ammonia and ascaroside on the trap morphogenesis remains unclear. This study demonstrated that the combination of nitrogenous substances with nematode-derived ascarosides led to higher trap production compared to the single inducing cues; notably, ammonia and Ascr#18 had the most synergistic effect on the trap in A. oligospora. Further, the deletion of ammonia transceptor Amt43 blocked trap formation against ammonia addition in A. oligospora but not for the ascaroside Ascr#18 induction. Moreover, ammonia addition could promote plasma endocytosis in the process of trap formation. In contrast, ascaroside addition would facilitate the stability of intracellular organization away from endocytosis. Therefore, there is a synergistic effect on trap induction from different nitrogenous and ascaroside signals.

Conidia Fusion: A Mechanism for Fungal Adaptation to Nutrient-Poor Habitats

Conidia fusion (CF) is a commonly observed structure in fungi. However, it has not been systematically studied. This study examined 2457 strains of nematode-trapping fungi (NTF) to explore the species specificity, physiological period, and physiological significance of CF. The results demonstrated that only six species of Arthrobotrys can form CF among the sixty-five tested NTF species. The studies on the model species Arthrobotrys oligospora (DL228) showed that CF occurred in both shed and unshed plus mature and immature conidia. Additionally, the conidia fusion rate (CFR) increased significantly with the decrease of nutrient concentration in habitats. The studies on the conidia fusion body (CFB) produced by A. oligospora (DL228) revealed that the more conidia contained in the CFB, the faster and denser the mycelia of the CFB germinated in weak nutrient medium and soil plates. On the one hand, rapid mycelial extension is beneficial for the CFB to quickly find new nutrient sources in habitats with uneven nutrient distribution. On the other hand, dense mycelium increases the contact area with the environment, improving the nutrient absorption efficiency, which is conducive to improving the survival rate of conidia in the weak nutrient environment. In addition, all species that form CF produce smaller conidia. Based on this observation, CF may be a strategy to balance the defects (nutrient deficiency) caused by conidia miniaturization.

Morphological and Phylogenetic Characterization of Five Novel Nematode-Trapping Fungi (Orbiliomycetes) from Yunnan, China

Nematode-trapping fungi are widely studied due to their unique morphological structure, survival strategy, and potential value in the biological control of harmful nematodes. During the identification of carnivorous fungi preserved in our laboratory, five novel nematode-trapping fungi were established and placed in the genera Arthrobotrys and Drehslerella based on morphological and multigene (ITS, TEF, and RPB2) phylogenetic analyses. A. hengjiangensis sp. nov. and A. weixiensis sp. nov. are characterized by producing adhesive networks to catch nematodes. Dr. pengdangensis sp. nov., Dr. tianchiensis sp. nov., and Dr. yunlongensis sp. nov. are characterized by producing constricting rings. Morphological descriptions, illustrations, taxonomic notes, and phylogenetic analysis are provided for all new taxa; a key for Drechslerella species is listed; and some deficiencies in the taxonomy and evolution study of nematode-trapping fungi are also discussed herein.

Recent Advances in Life History Transition with Nematode-Trapping Fungus Arthrobotrys oligospora and Its Application in Sustainable Agriculture

Parasitic nematodes cause great annual loss in the agricultural industry globally. Arthrobotrys oligospora is the most prevalent and common nematode-trapping fungus (NTF) in the environment and the candidate for the control of plant- and animal-parasitic nematodes. A. oligospora is also the first recognized and intensively studied NTF species. This review highlights the recent research advances of A. oligospora as a model to study the biological signals of the switch from saprophytism to predation and their sophisticated mechanisms for interacting with their invertebrate hosts, which is of vital importance for improving the engineering of this species as an effective biocontrol fungus. The application of A. oligospora in industry and agriculture, especially as biological control agents for sustainable purposes, was summarized, and we discussed the increasing role of A. oligospora in studying its sexual morph and genetic transformation in complementing biological control research.

Molecular Defense Response of Bursaphelenchus xylophilus to the Nematophagous Fungus Arthrobotrys robusta

Bursaphelenchus xylophilus causes pine wilt disease, which poses a serious threat to forestry ecology around the world. Microorganisms are environmentally friendly alternatives to the use of chemical nematicides to control B. xylophilus in a sustainable way. In this study, we isolated a nematophagous fungus-Arthrobotrys robusta-from the xylem of diseased Pinus massoniana. The nematophagous activity of A. robusta against the PWNs was observed after just 6 h. We found that B. xylophilus entered the trap of A. robusta at 24 h, and the nervous system and immunological response of B. xylophilus were stimulated by metabolites that A. robusta produced. At 30 h of exposure to A. robusta, B. xylophilus exhibited significant constriction, and we were able to identify xenobiotics. Bursaphelenchus xylophilus activated xenobiotic metabolism, which expelled the xenobiotics from their bodies, by providing energy through lipid metabolism. When PWNs were exposed to A. robusta for 36 h, lysosomal and autophagy-related genes were activated, and the bodies of the nematodes underwent disintegration. Moreover, a gene co-expression pattern network was constructed by WGCNA and Cytoscape. The gene co-expression pattern network suggested that metabolic processes, developmental processes, detoxification, biological regulation, and signaling were influential when the B. xylophilus specimens were exposed to A. robusta. Additionally, bZIP transcription factors, ankyrin, ATPases, innexin, major facilitator, and cytochrome P450 played critical roles in the network. This study proposes a model in which mobility improved whenever B. xylophilus entered the traps of A. robusta. The model will provide a solid foundation with which to understand the molecular and evolutionary mechanisms underlying interactions between nematodes and nematophagous fungi. Taken together, these findings contribute in several ways to our understanding of B. xylophilus exposed to microorganisms and provide a basis for establishing an environmentally friendly prevention and control strategy.

Establishment of Arthrobotrys flagrans as biocontrol agent against the root pathogenic nematode Xiphinema index

Plant-parasitic nematodes cause devastating agricultural damage worldwide. Only a few synthetic nematicides can be used and their application is limited in fields. Therefore, there is a need for sustainable and environment-friendly alternatives. Nematode-trapping fungi (NTF) are natural predators of nematodes. They capture and digest them with their hyphae and are starting to being used as bio-control agents. In this study, we applied the NTF Arthrobotrys flagrans (Duddingtonia flagrans) against the wine pathogenic nematode Xiphinema index. A. flagrans reduced the number of X. index juveniles in pot cultures of Ficus carica, an alternative host plant for X. index, significantly. Sodium-alginate pellets with A. flagrans spores were produced for vineyard soil inoculation under laboratory conditions. The NTF A. conoides, A. musiformis and A. superba were enriched from several soil samples, showing their natural presence. Trap formation is an energy-consuming process and depends upon various biotic and abiotic stimuli. Here, we show that bacteria of the genus Delftia, Bacillus, Pseudomonas, Enterobacter and Serratia induced trap formation in NTF like A. conoides and A. oligospora but not in A. flagrans in the absence of nematodes. The application of NTF along with such bacteria could be a combinatorial way of efficient biocontrol in nematode-infested soil.

Microbes vs. Nematodes: Insights into Biocontrol through Antagonistic Organisms to Control Root-Knot Nematodes

Root-knot nematodes (Meloidogyne spp.) are sedentary endoparasites that cause severe economic losses to agricultural crops globally. Due to the regulations of the European Union on the application of nematicides, it is crucial now to discover eco-friendly control strategies for nematode management. Biocontrol is one such safe and reliable method for managing these polyphagous nematodes. Biocontrol agents not only control these parasitic nematodes but also improve plant growth and induce systemic resistance in plants against a variety of biotic stresses. A wide range of organisms such as bacteria, fungi, viruses, and protozoans live in their natural mode as nematode antagonists. Various review articles have discussed the role of biocontrol in nematode management in general, but a specific review on biocontrol of root-knot nematodes is not available in detail. This review, therefore, focuses on the biocontrol of root-knot nematodes by discussing their important known antagonists, modes of action, and interactions.

Natural compounds derived from Brassicaceae plants as an alternative to synthetic fungicides and their influence on soil fungus diversity

BACKGROUND

The study aimed to develop a new formulation based on active substances of natural origin to protect plant seedlings against fungal pathogens, and to evaluate the effect of this formulation on fungal communities in arable soil.

RESULTS

Coating seeds of common crop plants with a p-coumaric acid (p-CA)-based preparation resulted in a significant reduction in the growth of most of the tested pathogens. When applied to soil, both the p-CA-based formulation and Porter 250 EC had a similar overall effect on soil fungal communities and significantly altered the structure of fungal communities at all of the times examined. Shifts in the fungal community composition concerned less than 2% of the total number of amplicon sequence variants (ASVs). The strongest impact of the formulations on soil microbiota was recorded at the fourth week of treatment. Two ASVs assigned to Botrytis and Chromelosporium, known as plant pathogens, and an unidentified ASV from Diversisporales encompassing the arbuscular mycorrhizal fungi (AMF), were significantly depleted in soil samples treated with p-CA in comparison with Porter 250 EC.

CONCLUSION

The p-CA-based preparation has the potential to be used as an alternative to synthetic fungicides. It shows a similar effect to Porter 250 EC on the organization of soil communities, determining changes in the character of the communities of fungi in general, at any given time. Moreover, p-CA caused a reduction in ASVs belonging to Botrytis and Chromelosporium (plant pathogens) and ASVs of Diversisporales (containing arbuscular mycorrhizal fungi) in comparison with the commercial compound that was analyzed. © 2022 Society of Chemical Industry.

Biological agents and their metabolites to control <i>Meloidogyne</i> spp. when growing vegetables (review)

Aim. Analysis of modern studies on the effectiveness of fungi and antagonist   bacteria   against   Meloidogyne   root‐knot   nematodes   on vegetable crops.

Materials and Methods. Studies of Russian and foreign scientists on the use of biological agents and their metabolites to control Meloidogyne spp. when growing vegetables have been carefully analysed.

Results.   The   harmfulness   of   gall   nematodes   on   vegetable   crops   is described.  Studies  on  the  most  pathogenic  species  of  Meloidogyne, including those common in Russia, are summarised. Information is given regarding  features  of  the  relationship  between  the  host  plant  and phytoparasites are highlighted. An analysis of the range of chemical and biological nematicides is presented. The problem of the lack of effective environmentally friendly products able to control root‐knot nematodes on vegetables, including  the  prospect of using  biological agents, has  been identified.   The   features   of   ongoing   research   on   the   study   of   the nematicidal activity of biological agents and their metabolites to control various   stages   of   development   of   Meloidogyne   species   have   been collected, analysed, systematised and described. The prospect of studying the mechanisms of action of microorganisms against root‐knot nematodes is substantiated in order to create new effective biological nematicides that allow the growth of high‐quality and healthy vegetable products.

Conclusion. Gall nematodes (Meloidogyne spp.) remain a current pest of soil‐grown  vegetables.  Scientists  are  actively  working  on  the  study  of nematophagous fungi and antagonist bacteria to create environmentally friendly  biological  nematicides.  With  proper  use,  biological  agents  and their metabolites can help protect plants from phytoparasites at the level of chemical nematicides and have an additional beneficial effect on the growth and development of vegetable crops.

 

Fungal Endophytes and Their Role in Agricultural Plant Protection against Pests and Pathogens

Virtually all examined plant species harbour fungal endophytes which asymptomatically infect or colonize living plant tissues, including leaves, branches, stems and roots. Endophyte-host interactions are complex and span the mutualist-pathogen continuum. Notably, mutualist endophytes can confer increased fitness to their host plants compared with uncolonized plants, which has attracted interest in their potential application in integrated plant health management strategies. In this review, we report on the many benefits that fungal endophytes provide to agricultural plants against common non-insect pests such as fungi, bacteria, nematodes, viruses, and mites. We report endophytic modes of action against the aforementioned pests and describe why this broad group of fungi is vitally important to current and future agricultural practices. We also list an extensive number of plant-friendly endophytes and detail where they are most commonly found or applied in different studies. This review acts as a general resource for understanding endophytes as they relate to potential large-scale agricultural applications.

Root-knot nematodes (Meloidogyne spp.) a threat to agriculture in Mexico: biology, current control strategies, and perspectives

Root-knot nematodes (RKN) are sedentary parasites of the roots of plants and are considered some of the most damaging pests in agriculture. Since RKN target the root vascular system, they provoke host nutrient deprivation and defective water transport, causing above-ground symptoms of growth stunting, wilting, chlorosis, and reduced crop yields. In Mexico RKN infestations are primarily dealt with by treating with synthetic chemically based nematicides that are preferred by farmers over available bioproducts. However, due to environmental and human health concerns chemical control is increasingly restricted. Biological control of RKNs can help reduce the use of chemical nematicides as it is achieved with antagonistic organisms, mainly bacteria, fungi, other nematodes, or consortia of diverse microorganisms, which control nematodes directly by predation and parasitism at different stages: eggs, juveniles, or adults; or indirectly by the action of toxic diffusible inhibitory metabolites. The need to increase agricultural production and reduce negative environmental impact creates an opportunity for optimizing biological control agents to suppress nematode populations, but this endeavour remains challenging as researchers around the world try to understand diverse control mechanisms, nematode and microbe life cycles, ecology, metabolite production, predatory behaviours, molecular and biochemical interactions, in order to generate attractive products with the approval of local regulatory bodies. Here, we provide a brief review of the biology of the genus Meloidogyne, biological control strategies, and a comparison between chemical and bioproducts in the Mexican market, and guidelines emitted by national agencies to ensure safety and effectiveness of new developments.

Biological control: An effective approach against nematodes using black pepper plants (Piper nigrum L.)

Black pepper (Piper nigrum L.) is one of the oldest spices in the world, additionally, it is highly demanded. Several biotic and abiotic variables pose black pepper production worldwide. Plant-parasitic nematodes play a key role among biotic factors, causing considerable economic losses and affecting the production. Different synthetic nematicides were used for controlling plant nematodes, however the majority of pesticides have been pulled from the market due to substantial non-target effects and environmental risks. As a result, the search for alternative eco-friendly agents for controlling plant-parasitic nematodes populations. Microbial agents are a precious option. In this review the bacterial and fungal agents used as an alternative nematicides, they were studied and confirmed as essential anti-microbial agents against plant nematodes which infected Piper nigrum L. This work examines the most common plant nematodes infected Piper nigrum L., with a focus on root knot and burrowing nematodes, in addition, how to control plant parasitic nematodes using microorganisms.

Phospholipase C (AoPLC2) regulates mycelial development, trap morphogenesis, and pathogenicity of the nematode-trapping fungus Arthrobotrys oligospora

AIMS

Phospholipase C (PLC) is a hydrolase involved in signal transduction in eukaryotic cells. This study aimed to understand the function of PLC in the nematode-trapping fungus Arthrobotrys oligospora.

METHODS AND RESULTS

Orthologous PLC (AoPLC2) of A. oligospora was functionally analysed using gene disruption and multi-phenotypic analysis. Disrupting Aoplc2 caused a deformation of partial hyphal cells (about 10%) and conidia (about 50%), decreased the number of nuclei in both conidia and hyphal cells, and increased the accumulation of lipid droplets. Meanwhile, the sporulation-related genes fluG and abaA were downregulated in ΔAoplc2 mutants than in the wild-type strain. Moreover, ΔAoplc2 mutants were more sensitive to osmotic stressors. Importantly, the number of traps, electron-dense bodies in traps, and nematicidal activity of ΔAoplc2 mutants were reduced, and the shape of the traps was deformed. In addition, AoPLC2 was involved in the biosynthesis of secondary metabolites in A. oligospora.

CONCLUSIONS

AoPLC2 plays an important role in the development of hyphae, spores, and cell nuclei, responses to stress, formation of traps, and predation of nematodes in A. oligospora.

SIGNIFICANCE AND IMPACT OF STUDY

This study reveals the various functions of phospholipase C and elucidates the regulation of trap morphogenesis in nematode-trapping fungi.