Biological Control Of Plant Parasitic Nematodes Research Articles

Biological Control of Plant Parasitic-Nematodes by Plant Growth Promoting-Rhizobacteria

Plant growth promoting-rhizobacteria (PGPR) contributes a significant part in crop health improvement including pest management. It also protects plants from parasitic nematodes damage by exhibiting biocontrol activity besides improving the growth of plants by supplying nutrients, producing phytohormones and inducing modification of plants metabolisms. PGPR decreases or inhibits the hatching of nematode juveniles and suppresses the nematodes development and reproduction by exhibiting various mechanisms such as hyperparasitism, antibiotic synthesis or antibiosis, substrate competition, synthesis of lytic enzymes and induction of resistance in plants. Hence, PGPR could be an efficient biological protective agent that protects agricultural and horticultural crop plants from the infestation of parasitic nematodes.

Soil Nematodes as a Means of Conservation of Soil Predatory Mites for Biocontrol

Numerous lab and field studies have reported the potential of soil predatory mites for the biological control of plant-parasitic nematodes and arthropods pests. Most of these studies have utilized biocontrol agents in augmentative releases, essentially controlling the pest with the released predators. While this may be a valid approach, we hypothesize that conservation of soil mite predators with available, suitable, and accessible free-living nematodes as prey, will provide better agricultural ecosystem performance and long-range sustainability. In this manuscript, we review the relevant studies on soil predatory mite–nematode interactions and highlight their potential for conservation biological control of soil-borne pests. Additionally, we emphasize the importance of implementing environmentally sound soil management practices for the sustainability and conservation of functional soil food webs.

Trichoderma harzianum and Trichoderma asperellum are potential biocontrol agents of Meloidogyne javanica in banana cv. Grande Naine

Biological control of plant-parasitic nematodes by Trichoderma has been widely studied, especially in annual crops such as soybean and cotton, but scarcely explored in the banana crop. Phytonematodes often attack banana plantations, and the species of Meloidogyne typically are the most frequent. Depending on the nematode population, they lead to yield losses or even plant death. Despite several Trichoderma commercial products registered in Brazil as biofungicides or bionematicides, there is a single one recommended to manage Meloidogyne incognita, with no approvals for M. javanica. The objective of this study was to evaluate two Trichoderma harzianum isolates (ALL42 and IBLF006) and the T. asperellum T00 strain as antagonists of M. javanica and as inducers of systemic resistance on bananas. Greenhouse experiments were conducted by treating seedlings of the Grande Naine susceptible cultivar with conidia suspension of the isolates. The enzymatic activity of CHId and GLUeon banana leaves was evaluated at 7, 14, and 21 days after inoculation (DAI). Plant growth and nematode population were evaluated at 60 DAI. T. harzianum ALL42 and T. harzianum IBFL006 reduced the M. javanica population on banana roots by up to 55.2 % and 67.9 %, respectively, in contrast to T. asperellum T00 that was inefficient. Enzymatic activity of CHI in plants non-inoculated with the nematode was higher at 14 DAI and decreased afterward. CHI and GLU activity were higher at 21 DAI in plants treated with isolate IBFL006 and grown in infested soil. The treatments did not promote plant growth. The effect of T. harzianum isolates was tested “in vitro” as filtrate or conidia suspension on mortality of J2 individuals. ALL42 and IFBL006 non-autoclaved filtrates promoted the highest M. javanica mortality rates of 59.6 %, and 68.8 % respectively.

Purpureocillium lilacinum an emergent pathogen: antifungal susceptibility of environmental and clinical strains

Purpureocillium lilacinum is a filamentous and hyaline fungus cosmopolitan, saprophytic, largely used in the biological control of plant-parasitic nematodes and insects, also considered an emerging and opportunistic human pathogen. The standard treatment for hyalohyphomycosis caused by P. lilacinum is not yet defined, since this fungus is resistant to different antifungals, in vitro and in vivo. The aim of this study was to evaluate and compare in vitro antifungal activity against environmental and clinical P. lilacinum isolates and our results demonstrated that these isolates can be resistant to newer generation triazoles, such as voriconazole, and to caspofungin, a drug of the echinocandin class. In summary, we highlight the importance of knowing the different susceptibility profiles of P. lilacinum isolates, and besides that, the emergence of uncommon human and animal opportunistic fungi, such P. lilacinum, especially during COVID-19, highlight the need for antifungal susceptibility testing of isolates since empirical therapy with different treatment schedules failed in great number of patients.

Nematicidal Effects of Volatile Organic Compounds from Microorganisms and Plants on Plant-Parasitic Nematodes.

Plant-parasitic nematodes (PPNs) are one of the most destructive plant pathogens worldwide, and controlling them is extremely challenging. Volatile organic compounds (VOCs), which naturally exist in plants and microorganisms, play an important role in the biological control of PPNs and are considered potential substances for the development of commercial nematicides. This paper summarizes the VOCs produced by microorganisms and plants as well as their toxic effects on PPNs. VOCs from 26 microbial strains and 51 plants that are active against nematodes from over the last decade were reviewed. Furthermore, the mechanisms of toxicity of some VOCs against PPNs are also illustrated.

AoPEX1 and AoPEX6 Are Required for Mycelial Growth, Conidiation, Stress Response, Fatty Acid Utilization, and Trap Formation in Arthrobotrys oligospora.

ABSTRACTArthrobotrys oligospora (A. oligospora) is a typical nematode-trapping (NT) fungus that can capture nematodes by producing adhesive networks. Peroxisomes are single membrane-bound organelles that perform multiple physiological functions in filamentous fungi. Peroxisome biogenesis proteins are encoded by PEX genes, and the functions of PEX genes in A. oligospora and other NT fungi remain largely unknown. Here, our results demonstrated that two PEX genes (AoPEX1 and AoPEX6) are essential for mycelial growth, conidiation, fatty acid utilization, stress tolerance, and pathogenicity in A. oligospora. AoPEX1 and AoPEX6 knockout resulted in a failure to produce traps, conidia, peroxisomes, and Woronin bodies and damaged cell walls, reduced autophagosome levels, and increased lipid droplet size. Transcriptome data analysis showed that AoPEX1 and AoPEX6 deletion resulted in the upregulation of the proteasome, membranes, ribosomes, DNA replication, and cell cycle functions, and the downregulation of MAPK signaling and nitrogen metabolism. In summary, our results provide novel insights into the functions of PEX genes in the growth, development, and pathogenicity of A. oligospora and contribute to the elucidation of the regulatory mechanism of peroxisomes in trap formation and lifestyle switching in NT fungi.IMPORTANCE Nematode-trapping (NT) fungi are important resources for the biological control of plant-parasitic nematodes. They are widely distributed in various ecological environments and capture nematodes by producing unique predatory organs (traps). However, the molecular mechanisms of trap formation and lifestyle switching in NT fungi are still unclear. Here, we provided experimental evidence that the AoPEX1 and AoPEX6 genes could regulate mycelial growth and development, trap formation, and nematode predation of A. oligospora. We further analyzed the global transcription level changes of wild-type and mutant strains using RNA-seq. This study highlights the important role of peroxisome biogenesis genes in vegetative growth, conidiation, trap formation, and pathogenicity, which contribute to probing the mechanism of organelle development and trap formation of NT fungi and lays a foundation for developing high-efficiency nematode biocontrol agents.

Role of Trichoderma as a biocontrol agent (BCA) of phytoparasitic nematodes and plant growth inducer

Nematodes as plant pathogens adversely affect food, fiber, and biofuels production by causing plant diseases. A variety of chemical nematicides are being applied to soil, seeds, or foliage with a goal of disease prevention. Despite the proven efficacy of these chemicals against plant-parasitic nematodes, factors like prolonged residual toxicity to human health, environmental pollution, and the risk of resistance development can’t be neglected. Due to these reasons, many chemicals are being banned continuously or delimited in the crop production system. Alternatively, the need for long-term strategies and integrative approaches to control plant diseases is inevitable. Trichoderma spp. are widely used in agriculture as biological control agents (BCA). To our knowledge, either very little or no information available on the most recent developments regarding Trichoderma-mediated biological control of plant-parasitic nematodes. This review summarizes the recent advances in using Trichoderma as BCA and plant growth regulator with a special focus on plant-parasitic nematodes.

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.

Combined releases of soil predatory mites and provisioning of free-living nematodes for the biological control of root-knot nematodes on ‘Micro Tom tomato’

Soil predatory mites feed on a diverse diet making them excellent candidates for conservation biocontrol. Free-living nematodes (FLN) are commonly found in soils and serve as prey for many acarine predators. Our goal was to determine whether conservation biological control of plant-parasitic nematodes by predators could be enhanced by provisioning FLN with their culture medium (FLNCM) under semi-field conditions. We conducted two experiments on dwarf tomato plants, the first until the beginning of flowering and the second until harvest. The treatments evaluated were with and without: 1) the root-knot nematode Meloidogyne incognita, 2) the predator Stratiolaelaps scimitus, and 3) the FLN Rhabditella axei in its culture medium. In both experiments, gall abundance was lowest in the combined treatment of FLN and predators. Similar reduction in gall abundance occurred when only predators or only FLNCM was added to the soil mix. Additionally, in the FLNCM treatment, foliar macronutrients N and K were significantly higher than the negative control. Our original aim was to use FLN as a supplementary food source for predators in conservation IPM. Based on the significant reduction in gall numbers, and the increase in foliar macronutrients, it is clear that the FLNCM treatment played additional roles. Finally, for demonstration, the predation of M. incognita was visualized in high resolution imaging using a low-temperature-scanning electron microscope. Accordingly, we recommend that future research focus on identifying soil amendments that will foster the establishment of beneficial microbiota, FLN and soil predators for the conservation biological control of soil pests.

Mycorrhizas reduce tomato root penetration by false root-knot nematode Nacobbus aberrans

Arbuscular mycorrhizal fungi (AMF) are considered as a possible alternative for the biological control of plant-parasitic nematodes. The false root-knot nematode Nacobbus aberrans is an endoparasite that induces the formation of galls in plant roots and causes severe damage to crops of economic importance. The purpose of the study was to evaluate the effect of the individual and combined application of two AMF species (Rhizophagus intraradices and Funneliformis mosseae) on the tomato root penetration of N. aberrans second-stage juveniles (J2). Forty-five days after the application of AMF, 300 J2 were inoculated per plant. Tomato roots were analyzed after 4, 8 and 12days in order to quantify the nematodes that had invaded them. Plants inoculated with AMF presented a lower number of juveniles within the roots compared with non-mycorrhizal plants. No significant differences were observed between the individual and combined application of AMF regarding the number of nematode juveniles. The use of R. intraradices and F. mosseae (both individually and combined) reduced the entry of nematodes in tomato roots. The antagonistic effect of AMF on the invasion of N. aberrans J2 is reported for the first time.

Biological Control of Meloidogyne incognita by Spore-forming Plant Growth-promoting Rhizobacteria on Cotton.

In the past decade, increased attention has been placed on biological control of plant-parasitic nematodes using various fungi and bacteria. The objectives of this study were to evaluate the potential of 662 plant growth-promoting rhizobacteria (PGPR) strains for mortality to Meloidogyne incognita J2 in vitro and for nematode management in greenhouse, microplot, and field trials. Results indicated that the mortality of M. incognita J2 by the PGPR strains ranged from 0 to 100% with an average of 39%. Among the PGPR strains examined, 212 of 662 strains (or 33%) caused significantly greater mortality percent of M. incognita J2 than the untreated control. Bacillus was the major genus initiating a greater mortality percentage when compared with the other genera. In subsequent trials, B. velezensis strain Bve2 reduced M. incognita eggs per gram of cotton root in the greenhouse trials at 45 days after planting (DAP) similarly to the commercial standards Abamectin and Clothianidin plus B. firmus I-1582. Bacillus mojavensis strain Bmo3, B. velezensis strain Bve2, B. subtilis subsp. subtilis strain Bsssu3, and the Mixture 2 (Abamectin + Bve2 + B. altitudinis strain Bal13) suppressed M. incognita eggs per gram of root in the microplot at 45 DAP. Bacillus velezensis strains Bve2 and Bve12 also increased seed-cotton yield in the microplot and field trials. Overall, results indicate that B. velezensis strains Bve2 and Bve12, B. mojavensis strain Bmo3, and Mixture 2 have potential to reduce M. incognita population density and to enhance growth of cotton when applied as in-furrow sprays at planting.

Nuclear receptor nhr-48 is required for pathogenicity of the second stage (J2) of the plant parasite Meloidogyne incognita

Nuclear receptors (NRs) are a diverse class of transcription factors, which are involved in regulating a large number of physiological events in metazoans. However, the function of NRs is poorly understood in plant-parasitic nematodes. Here, members of the NR1J+K group of NRs in nematodes, including the free-living and plant parasites, were examined and phylogenetically analyzed. We found that the number of members of the NR1J+K group in plant-parasitic nematodes was less than that in the free-living nematodes, suggesting this reduction of NR1J+K group members in plant parasites maybe arose during the separation of the free-living and intermediately plant parasitic nematodes (Bursaphelenchus xylophilus). Interestingly, the DNA-binding domain (DBD) and ligand-binding domain (LBD) of NR1J+K members were separated into two gene locations in the plant parasites. Knockdown of Meloidogyne incognita WBMinc13296, the ortholog of Caenorhabditis elegans nhr-48 DBD, reduced infectivity, delayed development, and decreased reproductivity. J2 of M. incognita subjected to silencing of WBMinc13295, the orthologs of B. xylophilus nhr-48 LBD, exhibited developmental lag within the host and reduced reproductivity. This study provides new insights into the function of NRs and suggests that NRs are potential targets for developing effective strategies for biological control of plant-parasitic nematodes.

Biological control of plant-parasitic nematodes: soil ecosystem management in sustainable agriculture

Biological control of plant-parasitic nematodes: soil ecosystem management in sustainable agriculture

Measuring abundance, diversity and parasitic ability in two populations of the nematophagous fungus Pochonia chlamydosporia var. chlamydosporia

Abundance, genetic diversity and parasitic ability in the facultative nematode parasite Pochonia chlamydosporia var. chlamydosporia were compared in soils from two sites in Portugal under long-term tomato cultivation where root-knot nematodes (Meloidogyne sp.) were present. Fungal abundance assessed by selective agar or real-time quantitative PCR with specific primers was similar in both soils. PCR fingerprinting of isolates with ERIC primers indicated that the dominant P. c. var. chlamydosporia biotypes (profiles A and B) in both soils were very closely related, although a second biotype (profile C) was detected in one soil. When tomato plants infected with M. incognita were grown in the two soils, only profiles A and B were recovered from eggs. Primers based on polymorphisms in vcp1 demonstrated that isolates with profiles A and B were likely to prefer root-knot nematodes, whereas profile C preferred cyst nematodes. In the soil containing profiles A, B and C, egg parasitism by P. chlamydosporia was estimated at 1% using water agar plates with antibiotics but fewer than 0.2% of M. incognita eggs were shown to be infected with P. c. var. chlamydosporia when using species-specific β-tubulin-PCR primers. In contrast, the soil containing only profile B showed 22% egg parasitism on water agar plates and more than 2.5% of eggs were confirmed as P. c. var. chlamydosporia by species-specific β-tubulin-PCR primers. The results, which reveal limited diversity within the fungus at the two sites, are discussed in relation to biological control of plant-parasitic nematodes.

Bacteria used in the biological control of plant-parasitic nematodes: populations, mechanisms of action, and future prospects

As a group of important natural enemies of nematode pests, nematophagous bacteria exhibit diverse modes of action: these include parasitizing; producing toxins, antibiotics, or enzymes; competing for nutrients; inducing systemic resistance of plants; and promoting plant health. They act synergistically on nematodes through the direct suppression of nematodes, promoting plant growth, and facilitating the rhizosphere colonization and activity of microbial antagonists. This review details the nematophagous bacteria known to date, including parasitic bacteria, opportunistic parasitic bacteria, rhizobacteria, Cry protein-forming bacteria, endophytic bacteria and symbiotic bacteria. We focus on recent research developments concerning their pathogenic mechanisms at the biochemical and molecular levels. Increased understanding of the molecular basis of the various pathogenic mechanisms of the nematophagous bacteria could potentially enhance their value as effective biological control agents. We also review a number of molecular biological approaches currently used in the study of bacterial pathogenesis in nematodes. We discuss their merits, limitations and potential uses.

Modes of action associated with microbially inducedin plantasuppression of plant-parasitic nematodes

This article discusses the extensive research that has been conducted on the use of mutualistic bacterial and fungal endophytes for the biological control of plant-parasitic nematodes. This review deals in particular with the modes of action of multitrophic interactions involving endophytic bacteria or fungi that have biological control activity towards the root-knot nematode, Meloidogyne incognita, and the potato cyst nematode, Globodera pallida, on tomato or potato. The bacterial and fungal endophytes discussed here are those that: (1) have the ability to colonise the endorhiza at some point in their life-cycle; (2) can grow saprophytically in the soil or in the rhizosphere; and (3) have plant health promoting activity and antagonistic activity towards sedentary plant-parasitic nematodes.

In vitro soil receptivity assays to egg-parasitic nematophagous fungi

Soil application of nematophagous fungi for the biological control of plant-parasitic nematodes often fails, and in many cases it has been difficult to reisolate the agent delivered to the soil. A reason for these results could be the inability of the fungi to proliferate in soil. We used a soil–membrane technique to study the capacity of several isolates of the nematophagous fungi Pochonia chlamydosporia and Paecilomyces lilacinus to grow and establish in sterilized and nonsterilized sandy soils from SE Spain and Western Australia. Growth of all fungi tested was inhibited in nonsterilized soil, although there was intraspecific variability in sensitivity among isolates of the same species. With respect to hyphal density, P. chlamydosporia isolate 5 (from Italy) was the least inhibited in nonsterilized soil from both sites. Relative growth analyses confirmed this result for soil from SE Spain, while with this method, P. chlamydosporia isolate 4624 (from Australia) appeared to be least inhibited in the Australian soil. The results indicate that a soil can be more receptive to its indigenous isolates than to nonindigenous isolates. Apparently, soil microbiota can determine the ability of nematophagous fungi to proliferate in soil.

Approaches to Biological Control of Nematode Pests by Natural Products and Enemies

Summary In recent years, continuing environmental problems associated with the use of nematicides have resulted in a sense of urgency regarding the search for alternative methods of nematode control. Biological control of plant-parasitic nematodes with natural products from plants and animals, and soil organisms are alternative control tactics that are receiving increased interest among nematologists. Natural products include a number of plant parts, by-products, and residues when incorporating into soil, and plant-interculture with other crop plants, crop rotation with non-host or poor host of nematodes, green manuring and other organic manures. Nemato-toxic compounds of the different plants are released through volatilization, exudation, leaching and decomposition. Natural enemies as bio-control agents to nematodes include bacterial and fungal parasites, predatory nematodes and soil invertebrates. The beneficial effects of natural products have been generally considered to be due to direct or indirect s...

Rhizosphere Interactions and the Exploitation of Microbial Agents for the Biological Control of Plant-Parasitic Nematodes.

A range of specialist and generalist microorganisms in the rhizosphere attacks plant-parasitic nematodes. Plants have a profound effect on the impact of this microflora on the regulation of nematode populations by influencing both the dynamics of the nematode host and the structure and dynamics of the community of antagonists and parasites in the rhizosphere. In general, those organisms that have a saprophytic phase in their life cycle are most affected by environmental conditions in the rhizosphere, but effects on obligate parasites have also been recorded. Although nematodes influence the colonization of roots by pathogenic and beneficial microorganisms, little is known of such interactions with the natural enemies of nematodes in the rhizosphere. As nematodes influence the quantity and quality of root exudates, they are likely to affect the physiology of those microorganisms in the rhizosphere; such changes may be used as signals for nematode antagonists and parasites. Successful biological control strategies will depend on a thorough understanding of these interactions at the population, organismal, and molecular scale.

Roles of organic soil amendments and soil organisms in the biological control of plant-parasitic nematodes: a review

Organic soil amendments stimulate the activities of microorganisms that are antagonistic to plant-parasitic nematodes. The decomposition of organic matter results in accumulation in the soils of specific compounds that may be nematicidal. Amendments are mainly bio-products and wastes from industrial, agricultural, biological and other activities. Control of plant-parasitic nematodes can be by improvements of soil structure and fertility, alteration of the level of plant-resistance, release of nemato-toxic compounds), parasites (fungi and bacteria) and other nematode antagonistic (biological control agents). The mode of action of organic amendments leading to plant disease control and stimulation of microorganisms is complex and dependent on the nature of the amendments.