Mechanisms Involved in Nematode Control by Endophytic Fungi

How the root bacterial community of Ficus tikoua responds to nematode infection: enrichments of nitrogen-fixing and nematode-antagonistic bacteria in the parasitized organs

Plant-parasitic nematodes (PPNs) are among the most damaging pathogens to host plants. Plants can modulate their associated bacteria to cope with nematode infections. The tritrophic plant-nematode-microbe interactions are highly taxa-dependent, resulting in the effectiveness of nematode agents being variable among different host plants. Ficus tikoua is a versatile plant with high application potential for fruits or medicines. In recent years, a few farmers have attempted to cultivate this species in Sichuan, China, where parasitic nematodes are present. We used 16S rRNA genes to explore the effects of nematode parasitism on root-associated bacteria in this species. Our results revealed that nematode infection had effects on both endophytic bacterial communities and rhizosphere communities in F. tikoua roots, but on different levels. The species richness increased in the rhizosphere bacterial communities of infected individuals, but the community composition remained similar as compared with that of healthy individuals. Nematode infection induces a deterministic assembly process in the endophytic bacterial communities of parasitized organs. Significant taxonomic and functional changes were observed in the endophytic communities of root knots. These changes were characterized by the enrichment of nitrogen-fixing bacteria, including Bradyrhizobium, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, and nematode-antagonistic bacteria, such as Pseudonocardia, Pseudomonas, Steroidobacter, Rhizobacter, and Ferrovibrio. Our results would help the understanding of the tritrophic plant-nematode-bacterium interactions in host plants other than dominant crops and vegetables and would provide essential information for successful nematode management when F. tikoua were cultivated on large scales.

Grass-Endophyte Interactions and Their Associated Alkaloids as a Potential Management Strategy for Plant Parasitic Nematodes

Claviceptaceous endophytic fungi in the genus Epichloë mostly form a symbiotic relationship with cool-season grasses. Epichloë spp. are capable of producing bioactive alkaloids such as peramines, lolines, ergot alkaloids, and indole-diterpenes, which protect the host plant from herbivory by animals, insects, and nematodes. The host also benefits from enhanced tolerance to abiotic stresses, such as salt, drought, waterlogging, cold, heavy metals, and low nitrogen stress. The bioactive alkaloids produced can have both direct and indirect effects towards plant parasitic nematodes. Direct interaction with nematodes' motile stages can cause paralysis (nematostatic effect) or death (nematicidal effect). Indirectly, the metabolites may induce host immunity which inhibits feeding and subsequent nematode development. This review highlights the different mechanisms through which this interaction and the metabolites produced have been explored in the suppression of plant parasitic nematodes and also how the specific interactions between different grass genotypes and endophyte strains result in variable suppression of different nematode species. An understanding of the different grass-endophyte interactions and their successes and failures in suppressing various nematode species is essential to enable the proper selection of grass-endophyte combinations to identify the alkaloids produced, concentrations required, and determine which nematodes are sensitive to which specific alkaloids.

Revolutionizing nematode management to achieve global food security goals - An overview

Nematodes are soil-dwelling organisms that inflict substantial damage to crops, resulting in significant declines in agricultural productivity. Consequently, they are recognized as one of the primary contributors to global crop damage, with profound implications for food security. Nematology research assumes a pivotal role in tackling this issue and safeguarding food security. The pursuit of nematology research focused on mitigating nematode-induced crop damage and promoting sustainable agriculture represents a fundamental strategy for enhancing food security. Investment in nematology research is crucial to advance food security objectives by identifying and managing nematode species, developing novel technologies, comprehending nematode ecology, and strengthening the capabilities of researchers and farmers. This endeavor constitutes an indispensable step toward addressing one of the most pressing challenges in achieving global food security and promoting sustainable agricultural practices. Primarily, research endeavors facilitate the identification of nematode species responsible for crop damage, leading to the development of effective management strategies. These strategies encompass the utilization of resistant crop varieties, implementation of cultural practices, biological control, and chemical interventions. Secondly, research efforts contribute to the development of innovative technologies aimed at managing nematode populations, such as gene editing techniques that confer resistance to nematode infestations in crops. Additionally, the exploration of beneficial microbes, such as certain fungi and bacteria, as potential biocontrol agents against nematodes, holds promise. The study of nematode ecology represents a foundational research domain that fosters a deeper comprehension of nematode biology and ecological interactions. This knowledge is instrumental in devising precise and efficacious management strategies.

Endophytic fungi: Unravelling plant-endophyte interaction and the multifaceted role of fungal endophytes in stress amelioration

Endophytic fungi colonize interior plant tissue and mostly form mutualistic associations with their host plant. Plant-endophyte interaction is a complex mechanism and is currently a focus of research to understand the underlying mechanism of endophyte asymptomatic colonization, the process of evading plant immune response, modulation of gene expression, and establishment of a balanced mutualistic relationship. Fungal endophytes rely on plant hosts for nutrients, shelter, and transmission and improve the host plant's tolerance against biotic stresses, including -herbivores, nematodes, bacterial, fungal, viral, nematode, and other phytopathogens. Endophytic fungi have been reported to improve plant health by reducing and eradicating the harmful effect of phytopathogens through competition for space or nutrients, mycoparasitism, and through direct or indirect defense systems by producing secondary metabolites as well as by induced systemic resistance (ISR). Additionally, for efficient crop improvement, practicing them would be a fruitful step for a sustainable approach. This review article summarizes the current research progress in plant-endophyte interaction and the fungal endophyte mechanism to overcome host defense responses, their subsequent colonization, and the establishment of a balanced mutualistic interaction with host plants. This review also highlighted the potential of fungal endophytes in the amelioration of biotic stress. We have also discussed the relevance of various bioactive compounds possessing antimicrobial potential against a variety of agricultural pathogens. Furthermore, endophyte-mediated ISR is also emphasized.

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.

Polydomus karssenii gen. nov. sp. nov. is a dark septate endophyte with a bifunctional lifestyle parasitising eggs of plant parasitic cyst nematodes (Heterodera spp.)

In this study fungal strains were investigated, which had been isolated from eggs of the cereal cyst nematode Heterodera filipjevi, and roots of Microthlaspi perfoliatum (Brassicaceae). The morphology, the interaction with nematodes and plants and the phylogenetic relationships of these strains originating from a broad geographic range covering Western Europe to Asia Minor were studied. Phylogenetic analyses using five genomic loci including ITSrDNA, LSUrDNA, SSUrDNA, rpb2 and tef1-α were carried out. The strains were found to represent a distinct phylogenetic lineage most closely related to Equiseticola and Ophiosphaerella, and Polydomus karssenii (Phaeosphaeriaceae, Pleosporales) is introduced here as a new species representing a monotypic genus. The pathogenicity tests against nematode eggs fulfilled Koch's postulates using in vitro nematode bioassays and showed that the fungus could parasitise its original nematode host H. filipjevi as well as the sugar beet cyst nematode H. schachtii, and colonise cysts and eggs of its hosts by forming highly melanised moniliform hyphae. Light microscopic observations on fungus-root interactions in an axenic system revealed the capacity of the same fungal strain to colonise the roots of wheat and produce melanised hyphae and microsclerotia-like structure typical for dark septate endophytes. Confocal laser scanning microscopy further demonstrated that the fungus colonised the root cells by predominant intercellular growth of hyphae, and frequent formation of appressorium-like as well as penetration peg-like structures through internal cell walls surrounded by callosic papilla-like structures. Different strains of the new fungus produced a nearly identical set of secondary metabolites with various biological activities including nematicidal effects irrespective of their origin from plants or nematodes.

Meloidogyne enterolobii risk to agriculture, its present status and future prospective for management

Meloidogyne enterolobii, commonly known as guava root-knot nematode, poses risk due to its widespread distribution and extensive host range. This species is recognized as the most virulent root-knot nematode (RKN) species because it can emerge and breed in plants that have resistance to other tropical RKNs. They cause chlorosis, stunting, and yield reductions in host plants by producing many root galls. It is extremely challenging for farmers to diagnose due to the symptoms' resemblance to nutritional inadequacies. This pathogen has recently been considered a significant worldwide threat to agricultural production. It is particularly challenging to diagnose a M. enterolobii due to the similarities between this species and other RKN species. Identified using traditional morphological and molecular techniques, which is a crucial first in integrated management. Chemical control, biological control, the adoption of resistant cultivars, and cultural control have all been developed and effectively utilized to combat root-knot nematodes in the past. The object of this study was to get about the geographical distribution, host plants, symptoms, identification, and control techniques of M. enterolobii and recommend future initiatives to progress its management.

Two new root endophyte and nematode cyst parasite species of the widely distributed genus Laburnicola

Fungal root endophytes, including the common form group of dark septate endophytes (DSEs), represent different taxonomic groups with potentially diverse life strategies. During surveys of DSE communities and of nematode cysts colonizing fungi, isolates representing Laburnicola (Didymosphaeriaceae, Pleosporales) lineages were discovered. Here we carried out a comprehensive study of the phylogenetic relationships and taxonomy of fungi collected from plant roots in Hungary, Mongolia, and Kazakhstan and from eggs of the cereal cyst nematode Heterodera filipjevi in Turkey. In addition to the study of the morphology and culture characteristics of the strains, four loci (internal transcribed spacer, partial large and small subunit regions of nuclear ribosomal DNA and partial translation elongation factor 1-alpha) were used to infer the molecular phylogenetic relationships of the strains within Laburnicola. The isolates were found to represent two distinct lineages, which are described here as novel species, Laburnicola nematophila and L. radiciphila. The interaction of the strains with plants and nematodes was examined using in vitro bioassays, which revealed endophytic interactions with the plant roots and parasitic interactions with the nematode eggs. Analyses of similar ITS sequences found in public databases revealed that members of the genus Laburnicola are widely distributed characteristic members of the plant microbiome, and they are reported as parasites of plant parasitic cyst nematodes here for the first time.

Harnessing microbial multitrophic interactions for rhizosphere microbiome engineering

The rhizosphere is a narrow and dynamic region of plant root-soil interfaces, and it's considered one of the most intricate and functionally active ecosystems on the Earth, which boosts plant health and alleviates the impact of biotic and abiotic stresses. Improving the key functions of the microbiome via engineering the rhizosphere microbiome is an emerging tool for improving plant growth, resilience, and soil-borne diseases. Recently, the advent of omics tools, gene-editing techniques, and sequencing technology has allowed us to unravel the entangled webs of plant-microbes interactions, enhancing plant fitness and tolerance to biotic and abiotic challenges. Plants secrete signaling compounds with low molecular weight into the rhizosphere, that engage various species to generate a massive deep complex array. The underlying principle governing the multitrophic interactions of the rhizosphere microbiome is yet unknown, however, some efforts have been made for disease management and agricultural sustainability. This review discussed the intra- and inter- microbe-microbe and microbe-animal interactions and their multifunctional roles in rhizosphere microbiome engineering for plant health and soil-borne disease management. Simultaneously, it investigates the significant impact of immunity utilizing PGPR and cover crop strategy in increasing rhizosphere microbiome functions for plant development and protection using omics techniques. The ecological engineering of rhizosphere plant interactions could be used as a potential alternative technology for plant growth improvement, sustainable disease control management, and increased production of economically significant crops.

Nematicidal Property of Clindamycin and 5-hydroxy-2-methyl Furfural (HMF) from the Banana Endophyte Bacillus velezensis (YEBBR6) Against Banana Burrowing Nematode Radopholus similis

Radopholus similis is a burrowing nematode which causes banana toppling disease and is of major economic threat for the banana production. Bacterial endophyte Bacillus velezensis (YEBBR6) produce biomolecules like 5-hydroxy-2-methyl furfural (HMF) and clindamycin in during interaction with Fusarium oxysporum f.sp. cubense. Molecular modelling and docking studies were performed on Radopholus similis protein targets such as calreticulin, cathepsin S-like cysteine proteinase, β-1,4 -endoglucanase, reticulocalbin, venom allergen-like protein and serine carboxypeptidase to understand the mode of action of HMF and clindamycin against Radopholus similis. Structurally validated protein targets of R. similis were docked with biomolecules through AutoDock Vina module in PyRx 0.8 software to predict the binding energy of ligand and target protein. Among the chosen six targets, docking analysis revealed that clindamycin had the maximum binding affinity for β-1,4-endoglucanase (- 7.2 kcal/mol), reticulocalbin (- 7.5 kcal/mol) and serine carboxypeptidase (- 6.9 kcal/mol) in comparison with HMF and the nematicide, carbofuran 3G. Besides, clindamycin also had the maximum binding energy for the target sites calreticulin and venom allergen-like protein compared to the small molecule HMF. Novel molecule, clindamycin produced by B. velezensis served as a potential inhibitor of the target sites associated in interrupting the functions of β-1,4-endoglucanase, reticulocalbin, serine carboxypeptidase, calreticulin, cathepsin S-like cysteine proteinase, and venom allergen-like proteins. Besides, increased binding affinity of clindamycin with the protein target sites facilitated to explore it as a novel nematicidal molecule for the management of banana burrowing nematode R. similis. Thus, present investigation confirmed that, the small molecules clindamycin can be explored for nematicidal activity.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-022-01011-2.

Novel Lead Compound Discovery from Aspergillus fumigatus 1T-2 against Meloidogyne incognita Based on a Chemical Ecology Study

To replace biohazardous nematicides, there is an ever-increasing need to identify natural product-based agents to contain root-knot nematodes (RKNs) in agriculture. In this chemical ecology study, an antagonistic fungus Aspergillus fumigatus 1T-2, which could cause the formation of withering of the gut and vacuole-like structures in the nematode body, was isolated based on the gradually increased antagonistic interactions between the soil fungi and RKNs. Based on these typical morphological characteristics, a potent nematode-antagonistic compound 2-furoic acid, which had a simple structure, was successfully identified from 1T-2 fermentation broth by liquid chromatography-mass spectrometry (LC-MS). 2-Furoic acid showed effective mortality activity in vitro, of which the LC₅₀ value to Megalaima incognita at 24 h was 37.75 μg/mL. 2-Furoic acid had similar mortality activity to the positive control fosthiazate at 30 μg/mL. Continuous 2-furoic acid exposure had obvious negative influences on both nematode vitality and egg hatchability. Notably, significant variations were observed in nematodes and eggs with 2-furoic acid treatment, which might be induced by novel nematocidal mechanisms. Furthermore, the 1T-2 fermentation broth and 2-furoic acid had significant control efficacy on M. incognita under the greenhouse test-tube assay. Overall, these findings provide valuable insights into the use of 2-furoic acid with biocontrol potential as a preferable lead structure for the development of innovative nematicides.

Soil Microbes Determine Outcomes of Pathogenic Interactions Between Radopholus similis and Fusarium oxysporum V5w2 in Tissue Culture Banana Rhizospheres Starved of Nitrogen, Phosphorus, and Potassium

The contributions of soil biota toward outcomes of pathogenic interactions between Radopholus similis and Fusarium oxysporum V5w2 in tissue culture banana plants starved of nitrogen (N), phosphorus (P), and potassium (K) were investigated. The study was based on three screenhouse factorial experiments (2 × 2 × 2) comprising of potted banana plants with or without R. similis, with or without F. oxysporum V5w2, and either grown in sterile or non-sterile soil. All plants in each of the three experiments received nutrient solutions that were deficient in N, P, or K, respectively. In all the three nutritional regimes, plants inoculated with R. similis were heavily colonized by the nematode with high percentage dead roots and necrosis, while their root biomasses were low. N-starved plants co-inoculated with R. similis and F. oxysporum V5w2 had lower percentage dead roots and tended to have numerically lower nematode density compared to those treated with R. similis only, especially in non-sterile soil. N-starved plants inoculated with R. similis had higher shoot dry weight, were taller with more leaves that were larger, compared to those not inoculated with the nematode. Plants grown in non-sterile soil had lower percentage dead roots, necrosis and R. similis density than those from sterile soil, regardless of the nutrient regime. N-starved plants from non-sterile soil were shorter with smaller leaves having decreased chlorophyll content and lower biomass, compared to those from sterile soil. By contrast, P and K starved plants from non-sterile soil were taller with larger leaves and more biomass, compared to those from sterile soil. Roots inoculated with R. similis had higher endophytic colonization by Fusarium spp., especially when co-inoculated with F. oxysporum V5w2 and grown in sterile soil among the N and K-starved plants. In conclusion, pathogenic interactions between R. similis and F. oxysporum V5w2 are predominantly suppressed by a complex of soil microbes that exert plant growth promoting effects in tissue culture banana plants through N, P, and K dependent processes. Nitrogen is the most important limiting factor in rhizosphere interactions between banana roots, beneficial microbes and the pathogens. Soil sterilization and the stringent aseptic tissue culture techniques still require the development of alternative innovative ways of conserving microbial services for sustainable agriculture.

Root Knot Nematode Presence and Its Integrated Management in Pomegranate Orchards Located in Indian Arid Areas

Nematodes are a serious problem across pomegranate-growing areas worldwide, but the severity is higher in light sandy soils of arid regions. The present study was carried out to explore the integrated approaches for the control of nematodes in pomegranate. Three different experiments were carried out during 2017–2020 to (a) delineate nematode abundance in major pomegranate areas, (b) screen pomegranate genotypes against nematode, and (c) assess the efficacy of integrated management for the control of root knot nematode in pomegranate. The survey results revealed that none of the pomegranate orchards were found to be free from nematode infestation. Moreover, the majority of the orchards (78%) showed moderate incidence (10.1 to 40%) of infestation. A significant yield reduction (40.2%) and a decrease in fruit size was observed in nematode-affected trees. Pattern of cuticular markings in the perineal area of the mature female confirmed the occurrence of Meloidogyne incognita only in all the surveyed orchard of pomegranate. All the evaluated genotypes and varieties were found susceptible to root knot nematodes, but the severity of the attack varied among them. Hence, more detailed screening is needed on a larger population. Nematode population (number of galls g−1 root) can be minimized significantly with the combined applications of Carbofuran at 20 g + Fluensulfone at 20 g per plant or Neemcake 500 g + Paecilomyceslilacinus at 25 mL + Carbofuran at 20 g + Fluensulfone at 20 g per plant in April and August.

Identification, Characterization, and Evaluation of Nematophagous Fungal Species of Arthrobotrys and Tolypocladium for the Management of Meloidogyne incognita

Root-knot nematodes belonging to the genus Meloidogyne are agriculturally important pests, and biocontrol strategies offer safer alternatives for their management. In the present study, two fungal species from Indian soils were identified as Arthrobotrys thaumasia and Tolypocladium cylindrosporum based on morphological characteristics and further confirmed using molecular markers. In vitro evaluation of A. thaumasia against M. incognita and Caenorhabditis elegans showed 82 and 73% parasitism, respectively, whereas T. cylindrosporum gave 65.2 and 57.7% parasitism, respectively. Similarly, culture filtrates of A. thaumasia caused 57.7 and 53.7% mortality of M. incognita and C. elegans, respectively, whereas T. cylindrosporum caused higher mortality of 87.3 and 64%, respectively. Besides, greenhouse evaluation of both fungi against M. incognita infecting tomato significantly reduced nematode disease burden reflecting parasitic success measured as the total number of galls, egg masses, eggs per egg mass, and derived nematode multiplication factor. Application of A. thaumasia and T. cylindrosporum reduced nematode multiplication factor by 80 and 95%, respectively, compared with control. General metabolite profiling of tested fungi using gas chromatography–mass spectrometry and ultra-performance liquid chromatography–quadrupole/time of flight mass spectrometry reported for the first time here showed presence of various volatile and non-volatile compounds with nematicidal activity, viz., trimethyl-heptadiene, methyl-hexadecanol, dodecadienal, decane, terpendole E, dodecane, acetamido-6-anthraquinone, and hexadecanol. Also, other compounds such as undecane, dibutyl-disulfide, octadecenal, paganin, talathermophilin, dactylarin, tolypyridone A, tolypyridone B, pyridoxatin, and destruxin were identified, reported in the literature to possess antibacterial, antifungal, and insecticidal properties. This is the first report of the occurrence of both fungi from India and pioneer demonstration of T. cylindrosporum for root-knot nematode management.

Optimizing Safe Approaches to Manage Plant-Parasitic Nematodes

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.

Mechanisms of silicon-induced fungal disease resistance in plants

Silicon (Si) acts as a beneficial element for plant growth and provides protection against abiotic and biotic stresses. Despite numerous reports on the beneficial role of Si in enhancing plant resistance to fungal pathogens, the underlying mechanisms remain largely unclear. Silicon shows antifungal activity; however, Si-induced improved disease resistance is partly manifested by the formation of Si polymerized mechanical obstruction under the cuticle and in cell walls, which prevents fungal ingress. Moreover, rapid production of defense compounds through secondary metabolic pathways is thought to be a key mechanism of Si-induced chemical defense against fungal pathogens beyond the physical barrier. Besides, improved mineral nutrition assures the healthy status of Si-supplied plants and a healthy plant exhibits better photosynthetic potential, antioxidant capacity and disease resistance. Multiple plant hormones and their crosstalk mediate the Si-induced basal as well as induced resistance; nonetheless, how root uptake of Si systemically modulates resistance to foliar diseases in low Si accumulating plants, needs in-depth investigation. Recent studies also indicate that Si influences effector-triggered immunity by affecting host recognition and/or limiting receptor-effector interactions. Here we review the role of Si in plant response to fungal pathogens. We also discuss and propose potential mechanisms of Si-induced enhanced disease resistance in plants. Finally, we identify some limitations of research approaches in addressing the beneficial roles of Si in biotic stress management.

Fungal and Bacterial Endophytes as Microbial Control Agents for Plant-Parasitic Nematodes

Endophytes are symbiotic microorganisms that colonize plant tissues and benefit plants in multiple ways including induced systemic resistance to biotic and abiotic stresses. Endophytes can be sustainable alternatives to chemical nematicides and enhance plant health in a variety of cropping and natural environments. Several in vitro and in vivo studies demonstrated the potential of multiple species of Fusarium and Bacillus against plant-parasitic nematodes in horticultural, agricultural, and fodder crops and in forestry. While there were efforts to commercialize some of the endophytes as bionematicides, a lack of good formulations with consistent field efficacy has been a major hurdle in commercializing endophytes for nematode control. Identification of efficacious and environmentally resilient strains, a thorough understanding of their modes of action, interactions with various biotic and abiotic factors, and developing strategies that improve their effectiveness are critical areas to advance the commercialization of bionematicides based on fungal and bacterial endophytes.

Root Endophytism by Pochonia chlamydosporia Affects Defense-Gene Expression in Leaves of Monocot and Dicot Hosts under Multiple Biotic Interactions

A study was carried out on the effect of the root endophytic fungus Pochonia chlamydosporia on plant systemic signal of defense related genes during fungal or nematode parasitism. Different biotic stress factors were examined, inoculating roots of dicot and monocot hosts with the endophyte, and measuring the expression of defense genes in leaves. A first greenhouse assay was carried out on expression of PAL, PIN II, PR1 and LOX D in leaves of tomato cv Tondino inoculated with Phytophthora infestans (CBS 120920), inoculating or not the roots of infected plants with P. chlamydosporia DSM 26985. In a second assay, plants of banana (Musa acuminata cv Grand Naine) were artificially infected with Fusarium oxysporum f. sp. cubense Tropical race 4 (TR4) and inoculated or not with DSM 26985. In a further experiment, banana plants were inoculated or not with P. chlamydosporia plus juveniles of the root knot nematode (RKN) Meloidogyne incognita. A similar assay was also carried out in vitro with adults and juveniles of the lesion nematode Pratylenchus goodeyi. Differential expression of the defense genes examined was observed for all plant-stress associations, indicative of early, upward systemic signals induced by the endophyte. Changes in expression profiles included a 5-fold down-regulation of PIN II at 2 dai in leaves of tomato plants treated with P. infestans and/or P. chlamydosporia, and the up-regulation of PAL by the endophyte alone, at 2 and 7 dai. In the TR4 assay, PR1 was significantly up-regulated at 7 dai in banana leaves, but only in the P. chlamydosporia treated plants. At 10 dai, PIN II expression was significantly higher in leaves of plants inoculated only with TR4. The banana-RKN assay showed a PR1 expression significantly higher than controls at 4 and 7 dai in plants inoculated with P. chlamydosporia alone, and a down-regulation at 4 dai in leaves of plants also inoculated with RKN, with a PR1 differential up-regulation at 10 dai. Pratylenchus goodeyi down-regulated PIN at 21 dai, with or without the endophyte, as well as PAL but only in presence of P. chlamydosporia. When inoculated alone, the endophyte up-regulated PR1 and LOX. The gene expression patterns observed in leaves suggest specific and time-dependent relationships linking host plants and P. chlamydosporia in presence of biotic stress factors, functional to a systemic, although complex, activation of defense genes.

Optimizing biological control agents for controlling nematodes of tomato in Egypt

Tomato is a major vegetable crop in Egypt and worldwide. Yet, many plant-parasitic nematodes (PPNs), especially Meloidogyne spp. and Rotylenchulus reniformis are a devastating threat to tomato cultivation in Egypt. This review addresses their biology, ecology, and economic importance from the standpoint of pest management. Soil treatment with synthetic nematicides has given some protection and enhanced tomato yields, but health hazards and environmental pollution are obstructing their intensive use. Moreover, some of such nematicides are being banned from the market. Therefore, safe biological control agents (BCAs) and their bioactive compounds should better be researched and developed to effectively replace hazardous nematicides. Abamectin, produced during the fermentation process of the actinomycete Streptomyces avermitilis, is recommended to manage PPNs of tomato in Egypt but further exploration should allocate where BCAs can reliably act with other agricultural inputs. Examples are given herein to streamline their development via synergistic interaction with compatible inputs such as chemicals and organic manure. Moreover, optimizing their delivery, interaction, and persistence under field conditions through novel ways such as the use of endophytic fungi and bacteria as well as bioactive molecules/nano-particles that have systemic activity in the nematode-infected plants should further be investigated and broadly disseminated.

Meloidogyne enterolobii, a Major Threat to Tomato Production: Current Status and Future Prospects for Its Management

The guava root-knot nematode, Meloidogyne enterolobii (Syn. M. mayaguensis), is an emerging pathogen to many crops in the world. This nematode can cause chlorosis, stunting, and reduce yields associated with the induction of many root galls on host plants. Recently, this pathogen has been considered as a global threat for tomato (Solanum lycopersicum L.) production due to the lack of known resistance in commercially accepted varieties and the aggressiveness of M. enterolobii. Both conventional morphological and molecular approaches have been used to identify M. enterolobii, an important first step in an integrated management. To combat root-knot nematodes, integrated disease management strategies such as crop rotation, field sanitation, biocontrol agents, fumigants, and resistant cultivars have been developed and successfully used in the past. However, the resistance in tomato varieties mediated by known Mi-genes does not control M. enterolobii. Here, we review the current knowledge on geographic distribution, host range, population biology, control measures, and proposed future strategies to improve M. enterolobii control in tomato.

Fungi-Nematode Interactions: Diversity, Ecology, and Biocontrol Prospects in Agriculture

Fungi and nematodes are among the most abundant organisms in soil habitats. They provide essential ecosystem services and play crucial roles for maintaining the stability of food-webs and for facilitating nutrient cycling. As two of the very abundant groups of organisms, fungi and nematodes interact with each other in multiple ways. Here in this review, we provide a broad framework of interactions between fungi and nematodes with an emphasis on those that impact crops and agriculture ecosystems. We describe the diversity and evolution of fungi that closely interact with nematodes, including food fungi for nematodes as well as fungi that feed on nematodes. Among the nematophagous fungi, those that produce specialized nematode-trapping devices are especially interesting, and a great deal is known about their diversity, evolution, and molecular mechanisms of interactions with nematodes. Some of the fungi and nematodes are significant pathogens and pests to crops. We summarize the ecological and molecular mechanisms identified so far that impact, either directly or indirectly, the interactions among phytopathogenic fungi, phytopathogenic nematodes, and crop plants. The potential applications of our understanding to controlling phytophagous nematodes and soilborne fungal pathogens in agricultural fields are discussed.

Changes in the core endophytic mycobiome of carrot taproots in response to crop management and genotype

Fungal endophytes can influence production and post-harvest challenges in carrot, though the identity of these microbes as well as factors affecting their composition have not yet been determined, which prevents growers from managing these organisms to improve crop performance. Consequently, we characterized the endophytic mycobiome in the taproots of three carrot genotypes that vary in resistance to two pathogens grown in a trial comparing organic and conventional crop management using Illumina sequencing of the internal transcribed spacer (ITS) gene. A total of 1,480 individual operational taxonomic units (OTUs) were identified. Most were consistent across samples, indicating that they are part of a core mycobiome, though crop management influenced richness and diversity, likely in response to differences in soil properties. There were also differences in individual OTUs among genotypes and the nematode resistant genotype was most responsive to management system indicating that it has greater control over its endophytic mycobiome, which could potentially play a role in resistance. Members of the Ascomycota were most dominant, though the exact function of most taxa remains unclear. Future studies aimed at overcoming difficulties associated with isolating fungal endophytes are needed to identify these microbes at the species level and elucidate their specific functional roles.

Recent Advances in the Development of Environmentally Benign Treatments to Control Root-Knot Nematodes

Root-knot nematodes (RKNs), Meloidogyne spp., are sedentary endoparasites that negatively affect almost every crop in the world. Current management practices are not enough to completely control RKN. Application of certain chemicals is also being further limited in recent years. It is therefore crucial to develop additional control strategies through the application of environmentally benign methods. There has been much research performed around the world on the topic, leading to useful outcomes and interesting findings capable of improving farmers' income. It is important to have dependable resources gathering the data produced to facilitate future research. This review discusses recent findings on the application of environmentally benign treatments to control RKN between 2015 and April 2020. A variety of biological control strategies, natural compounds, soil amendments and other emerging strategies have been included, among which, many showed promising results in RKN control in vitro and/or in vivo. Development of these methods continues to be an area of active research, and new information on their efficacy will continuously become available. We have discussed some of the control mechanisms involved and suggestions were given on maximizing the outcome of the future efforts.

Biological Control of Plant-Parasitic Nematodes by Filamentous Fungi Inducers of Resistance: Trichoderma, Mycorrhizal and Endophytic Fungi

Plant-parasitic-nematodes represent a major threat to the agricultural production of different crops worldwide. Due to the high toxicity of chemical nematicides, it is necessary to develop new control strategies against nematodes. In this respect, filamentous fungi can be an interesting biocontrol alternative. The genus Trichoderma, mycorrhizal and endophytic fungi are the main groups of filamentous fungi studied and used as biological control agents (BCAs) against nematodes as resistance inducers. They are able to reduce the damage caused by plant-parasitic nematodes directly by parasitism, antibiosis, paralysis and by the production of lytic enzymes. But they also minimize harm by space and resource-competition, by providing higher nutrient and water uptake to the plant, or by modifying the root morphology, and/or rhizosphere interactions, that constitutes an advantage for the plant-growth. Besides, filamentous fungi are able to induce resistance against nematodes by activating hormone-mediated (salicylic and jasmonic acid, strigolactones among others) plant-defense mechanisms. Additionally, the alteration of the transport of chemical defense components through the plant or the synthesis of plant secondary metabolites and different enzymes can also contribute to enhancing plant defenses. Therefore, the use of filamentous fungi of the mentioned groups as BCAs is a promising durable biocontrol strategy in agriculture against plant-parasitic nematodes.

Corn and Soybean Host Root Endophytic Fungi with Toxicity Toward the Soybean Cyst Nematode

Although fungal endophytes are commonly investigated for their ability to deter microbial plant pathogens, few studies have examined the activity of fungal root endophytes against nematodes. The soybean cyst nematode (SCN; Heterodera glycines), the most severe yield-limiting pathogen of soybean (Glycine max), is commonly managed through rotation of soybean with corn (Zea mays), a nonhost of the SCN. A total of 626 fungal endophytes were isolated from surface-sterilized corn and soybean roots from experimental plots in which soybean and corn had been grown under annual rotation and under 1, 3, 5, and 35 years of continuous monoculture. Fungal isolates were grouped into 401 morphotypes, which were clustered into 108 operational taxonomic units (OTUs) based on 99% sequence similarity of the full internal transcribed spacer region. Morphotype representatives within each OTU were grown in malt extract broth and in a secondary metabolite-inducing medium buffered with ammonium tartrate, and their culture filtrates were tested for nematicidal activity against SCN juveniles. A majority of OTUs containing isolates with nematicidal culture filtrates were in the order Hypocreales, with the genus Fusarium being the most commonly isolated nematicidal genus from corn and soybean roots. Less commonly isolated taxa from soybean roots included the nematophagous fungi Hirsutella rhossiliensis, Metacordyceps chlamydosporia, and Arthrobotrys iridis. Root endophytic fungal diversity in soybean was positively correlated with SCN density, suggesting that the SCN plays a role in shaping the soybean root endophytic community.

Commercial Formulates of Trichoderma Induce Systemic Plant Resistance to Meloidogyne incognita in Tomato and the Effect Is Additive to That of the Mi-1.2 Resistance Gene

Meloidogyne is the most damaging plant parasitic nematode genus affecting vegetable crops worldwide. The induction of plant defense mechanisms against Meloidogyne in tomato by some Trichoderma spp. strains has been proven in pot experiments, but there is no information for tomato bearing the Mi-1.2 resistance gene or for other important fruiting vegetable crops. Moreover, Trichoderma is mostly applied for managing fungal plant pathogens, but there is little information on its effect on nematode-antagonistic fungi naturally occurring in soils. Thus, several experiments were conducted to determine (i) the ability of two commercial formulates of Trichoderma asperellum (T34) and Trichoderma harzianum (T22) to induce systemic resistance in tomato and cucumber against an avirulent Meloidogyne incognita population in split-root experiments; (ii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to an avirulent M. incognita population in sterilized soil; and (iii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to a virulent M. incognita population in two suppressive soils in which Pochonia chlamydosporia is naturally present, and the effect of T34 on the level of P. chlamydosporia egg parasitism. Both Trichoderma formulates induced resistance to M. incognita in tomato but not in cucumber. In tomato, the number of egg masses and eggs per plant were reduced by 71 and 54% by T34, respectively. T22 reduced 48% of the number of eggs per plant but not the number of egg masses. T34 reduced the number of eggs per plant of the virulent M. incognita population in both resistant and susceptible tomato cultivars irrespective of the suppressive soil, and its effect was additive with the Mi-1.2 resistance gene. The percentage of fungal egg parasitism by P. chlamydosporia was not affected by the isolate T34 of T. asperellum.

Festulolium and fungal endophyte associations: host status for Meloidogyne incognita and nematotoxic plant extracts

Festulolium hybrids are forage grasses used worldwide in temperate climates. They are associated with the fungal endophyte Epichloë uncinata, which aids in nutrient uptake, drought tolerance, and production of metabolites that protect against parasites and herbivores. Epichloë uncinata produces loline alkaloids, which can deter insect pests. Festulolium has not been widely studied for susceptibility to plant-parasitic nematodes, so Festulolium lines, with and without fungal endophytes, were tested in the greenhouse for host status to the root-knot nematode Meloidogyne incognita. All were poor hosts, regardless of line or endophyte status. Pepper seedlings planted into soil following removal of the Festulolium plants were infected by nematodes, likely because of surviving nematodes from the original inoculation combined with some reproduction on Festulolium. Lolines were found in shoots and roots of all endophyte-associated lines, and some types of lolines in roots increased after nematode infection. Methanolic extracts from roots and shoots of a tested Festulolium line did not inhibit egg hatch, but killed nearly a third of second-stage juveniles whether an endophyte was present or not. Further studies would indicate whether these Festulolium lines aid in suppressing field populations of M. incognita.

Festulolium hybrids are forage grasses used worldwide in temperate climates. They are associated with the fungal endophyte Epichloë uncinata, which aids in nutrient uptake, drought tolerance, and production of metabolites that protect against parasites and herbivores. Epichloë uncinata produces loline alkaloids, which can deter insect pests. Festulolium has not been widely studied for susceptibility to plant-parasitic nematodes, so Festulolium lines, with and without fungal endophytes, were tested in the greenhouse for host status to the root-knot nematode Meloidogyne incognita. All were poor hosts, regardless of line or endophyte status. Pepper seedlings planted into soil following removal of the Festulolium plants were infected by nematodes, likely because of surviving nematodes from the original inoculation combined with some reproduction on Festulolium. Lolines were found in shoots and roots of all endophyte-associated lines, and some types of lolines in roots increased after nematode infection. Methanolic extracts from roots and shoots of a tested Festulolium line did not inhibit egg hatch, but killed nearly a third of second-stage juveniles whether an endophyte was present or not. Further studies would indicate whether these Festulolium lines aid in suppressing field populations of M. incognita.

Decreased Root-Knot Nematode Gall Formation in Roots of the Morning Glory Ipomoea tricolor Symbiotic with Ergot Alkaloid-Producing Fungal Periglandula Sp

Many species of morning glories (Convolvulaceae) form symbioses with seed-transmitted Periglandula fungal endosymbionts, which produce ergot alkaloids and may contribute to defensive mutualism. Allocation of seed-borne ergot alkaloids to various tissues of several Ipomoea species has been demonstrated, including roots of I. tricolor. The goal of this study was to determine if infection of I. tricolor by the Periglandula sp. endosymbiont affects Southern root-knot nematode (Meloidogyne incognita) gall formation and host plant biomass. We hypothesized that I. tricolor plants infected by Periglandula (E+) would develop fewer nematode-induced galls compared to non-symbiotic plants (E-). E+ or E- status of plant lines was confirmed by testing methanol extracts from individual seeds for endosymbiont-produced ergot alkaloids. To test the effects of Periglandula on nematode colonization, E+ and E- I. tricolor seedlings were grown in soil infested with high densities of M. incognita nematodes (N+) or no nematodes (N-) for four weeks in the greenhouse before harvesting. After harvest, nematode colonization of roots was visualized microscopically, and total gall number and plant biomass were quantified. Four ergot alkaloids were detected in roots of E+ plants, but no alkaloids were found in E- plants. Gall formation was reduced by 50% in E+ plants compared to E- plants, independent of root biomass. Both N+ plants and E+ plants had significantly reduced biomass compared to N- and E- plants, respectively. These results demonstrate Periglandula's defensive role against biotic enemies, albeit with a potential trade-off with host plant growth.

Effects of Cover Cropping on Microbial Communities Associated with Heterodera schachtii and Nematode Virulence

Nematode-resistant cover crops can suppress populations of plant-parasitic nematodes. Samples of a loamy and a sandy loam soil were collected from two sugar beet fields in Lower Saxonia, northern Germany (“Jeinsen” and “Gross Munzel”) to measure the effects of cover cropping on the population genetic structure and infectivity of Heterodera schachtii as well as the composition of soil microbial communities. These fields allowed for a comparison of cover cropping with Brassica species resistant to Heterodera schachtii to fallow. In a series of radish bioassays with H. schachtii populations from Jeinsen and Gross Munzel, ratios of second-stage juveniles in roots per eggs in soil were higher in soil from under Brassica cropping than from under fallow. In denaturing gradient gelelectrophoresis, profiles of the parasitism gene vap1 differed between Brassica and fallow treatments in both populations. At Gross Munzel, microbes of soils and within nematode cysts differed between Brassica and fallow areas. Specifically, the frequency and occurrence of isolates of Pochonia chlamydosporia and Exophiala salmonis were lower within the cysts from Brassica than from fallow treatments. Overall, cover cropping with resistant Brassica species affected the bacteria and fungi infecting the cysts and subsequently, the infectivity of the H. schachtii population. Cover crop effects on nematode virulence (vap1 gene) and microbial colonization of the cysts could affect long-term nematode population dynamics.

Pochonia chlamydosporia Induces Plant-Dependent Systemic Resistance to Meloidogyne incognita

Meloidogyne spp. are the most damaging plant parasitic nematodes for horticultural crops worldwide. Pochonia chlamydosporia is a fungal egg parasite of root-knot and cyst nematodes able to colonize the roots of several plant species and shown to induce plant defense mechanisms in fungal-plant interaction studies, and local resistance in fungal-nematode-plant interactions. This work demonstrates the differential ability of two out of five P. chlamydosporia isolates, M10.43.21 and M10.55.6, to induce systemic resistance against M. incognita in tomato but not in cucumber in split-root experiments. The M10.43.21 isolate reduced infection (32-43%), reproduction (44-59%), and female fecundity (14.7-27.6%), while the isolate M10.55.6 only reduced consistently nematode reproduction (35-47.5%) in the two experiments carried out. The isolate M10.43.21 induced the expression of the salicylic acid pathway (PR-1 gene) in tomato roots 7 days after being inoculated with the fungal isolate and just after nematode inoculation, and at 7 and 42 days after nematode inoculation too. The jasmonate signaling pathway (Lox D gene) was also upregulated at 7 days after nematode inoculation. Thus, some isolates of P. chlamydosporia can induce systemic resistance against root-knot nematodes but this is plant species dependent.

Bacteria isolated from the cuticle of plant-parasitic nematodes attached to and antagonized the root-knot nematode Meloidogyne hapla

Plant-parasitic nematodes are associated with specifically attached soil bacteria. To investigate these bacteria, we employed culture-dependent methods to isolate a representative set of strains from the cuticle of the infective stage (J2) of the root-knot nematode Meloidogyne hapla in different soils. The bacteria with the highest affinity to attach to J2 belonged to the genera Microbacterium, Sphingopyxis, Brevundimonas, Acinetobacter, and Micrococcus as revealed by 16S rRNA gene sequencing. Dynamics of the attachment of two strains showed fast adhesion in less than two hours, and interspecific competition for attachment sites. Isolates from the cuticle of M. hapla J2 attached to the lesion nematode Pratylenchus penetrans, and vice versa, suggesting similar attachment sites on both species. Removal of the surface coat by treatment of J2 with the cationic detergent CTAB reduced bacterial attachment, but did not prevent it. Some of the best attaching bacteria impaired M. hapla performance in vitro by significantly affecting J2 mortality, J2 motility and egg hatch. Most of the tested bacterial attachers significantly reduced the invasion of J2 into tomato roots, suggesting their beneficial role in soil suppressiveness against M. hapla.

Inhabiting plant roots, nematodes, and truffles-Polyphilus, a new helotialean genus with two globally distributed species

Fungal root endophytes, including the common group of dark septate endophytes (DSEs), represent different taxonomic groups and potentially diverse life strategies. In this study, we investigated two unidentified helotialean lineages found previously in a study of DSE fungi of semiarid grasslands, from several other sites, and collected recently from a pezizalean truffle ascoma and eggs of the cereal cyst nematode Heterodera filipjevi. The taxonomic positions and phylogenetic relationships of 21 isolates with different hosts and geographic origins were studied in detail. Four loci, namely, nuc rDNA ITS1-5.8S-ITS2 (internal transcribed spacer [ITS]), partial 28S nuc rDNA (28S), partial 18S nuc rDNA (18S), and partial RNA polymerase II second-largest subunit (RPB2), were amplified and sequenced for molecular phylogenetic analyses. Analyses of similar ITS sequences from public databases revealed two globally distributed lineages detected in several biomes from different geographic regions. The host interaction of isolates from nematodes was examined using in vitro bioassays, which revealed that the fungi could penetrate nematode cysts and colonize eggs of H. filipjevi, confirming observations from field-collected samples. This is the first report of a DSE, and we are not aware of other helotialean fungal species colonizing the eggs of a plant-parasitic nematode. Neither conidiomata and conidia nor ascomata formation was detected in any of the isolates. Based on molecular phylogenetic analyses, these isolates represent a distinct lineage within the Helotiales in the Hyaloscyphaceae. For this lineage, we propose here the new genus Polyphilus represented by two new species, P. sieberi and P. frankenii.

Modulation of plant chemistry by beneficial root microbiota

Beneficial root microbiota modulate plant chemistry and represent an untapped potential to discover new pathways involved in the biosynthesis of high value natural plant products.

Plant growth-promoting endophytic bacteria versus pathogenic infections: an example of Bacillus amyloliquefaciens RWL-1 and Fusarium oxysporum f. sp. lycopersici in tomato

Fungal pathogenic attacks are one of the major threats to the growth and productivity of crop plants. Currently, instead of synthetic fungicides, the use of plant growth-promoting bacterial endophytes has been considered intriguingly eco-friendly in nature. Here, we aimed to investigate the in vitro and in vivo antagonistic approach by using seed-borne endophytic Bacillus amyloliquefaciens RWL-1 against pathogenic Fusarium oxysporum f. sp. lycopersici. The results revealed significant suppression of pathogenic fungal growth by Bacillus amyloliquefaciens in vitro. Further to this, we inoculated tomato plants with RWL-1 and F. oxysporum f. sp. lycopersici in the root zone. The results showed that the growth attributes and biomass were significantly enhanced by endophytic-inoculation during disease incidence as compared to F. oxysporum f. sp. lycopersici infected plants. Under pathogenic infection, the RWL-1-applied plants showed increased amino acid metabolism of cell wall related (e.g., aspartic acid, glutamic acid, serine (Ser), and proline (Pro)) as compared to diseased plants. In case of endogenous phytohormones, significantly lower amount of jasmonic acid (JA) and higher amount of salicylic acid (SA) contents was recorded in RWL-1-treated diseased plants. The phytohormones regulation in disease incidences might be correlated with the ability of RWL-1 to produce organic acids (e.g., succinic acid, acetic acid, propionic acid, and citric acid) during the inoculation and infection of tomato plants. The current findings suggest that RWL-1 inoculation promoted and rescued plant growth by modulating defense hormones and regulating amino acids. This suggests that bacterial endophytes could be used for possible control of F. oxysporum f. sp. lycopersici in an eco-friendly way.

Isochromans and Related Constituents from the Endophytic Fungus Annulohypoxylon truncatum of Zizania caduciflora and Their Anti-Inflammatory Effects

Six new isochroman derivatives (annulohypoxylomans A-C, 1-3; annulohypoxylomanols A and B, 6 and 7; and annulohypoxyloside, 8), an isocoumarin (annulohypoxylomarin A, 4), and an azaphilone derivative (xylariphilone, 5) were isolated from an ethyl acetate extract derived from cultures of the endophytic fungus JS540 found in the leaves of Zizania caduciflora. The JS540 strain was identified as Annulohypoxylon truncatum. The structures of the isolated compounds were elucidated by one- and two-dimensional nuclear magnetic resonance and mass spectrometry and by comparison with related compounds from the literature. The anti-inflammatory activities of the isolated compounds were evaluated in lipopolysaccharide (LPS)-stimulated bone marrow-derived dendritic cells. Xylariphilone (5) exhibited significant inhibitory effects on LPS-induced interleukin (IL)-6, IL-12 p40, and tumor necrosis factor (TNF)-α production with IC₅₀ values of 5.3, 19.4, and 37.6 μM, respectively.

Bioactive secondary metabolites with multiple activities from a fungal endophyte

In order to replace particularly biohazardous nematocides, there is a strong drive to finding natural product‐based alternatives with the aim of containing nematode pests in agriculture. The metabolites produced by the fungal endophyte Fusarium oxysporum 162 when cultivated on rice media were isolated and their structures elucidated. Eleven compounds were obtained, of which six were isolated from a Fusarium spp. for the first time. The three most potent nematode‐antagonistic compounds, 4‐hydroxybenzoic acid, indole‐3‐acetic acid (IAA) and gibepyrone D had LC₅₀ values of 104, 117 and 134 μg ml⁻¹, respectively, after 72 h. IAA is a well‐known phytohormone that plays a role in triggering plant resistance, thus suggesting a dual activity, either directly, by killing or compromising nematodes, or indirectly, by inducing defence mechanisms against pathogens (nematodes) in plants. Such compounds may serve as important leads in the development of novel, environmental friendly, nematocides.