False Root-knot Nematode Research Articles

Antagonistic potential of endophytic fungi against Meloidogyne enterolobii, M. incognita and Nacobbus aberrans sensu lato

Root-knot nematodes limit horticultural crop production in Mexico where management is mainly based on nematicides that represent a risk to health and the environment. Thus, biological alternatives, such as the use of endophytic fungi, are currently being developed. The objective of this research was to isolate, identify and evaluate the antagonistic potential of endophytic fungi against the root-knot nematodes Meloidogyne enterolobii, M. incognita and the false root-knot nematode Nacobbus aberrans sensu lato (s.l.) occurring in Mexico. Endophytic fungi from chili pepper and tomato plants with a low root galling index were isolated from three localities in Sinaloa state (Villa Juárez, Valle de Culiacan and La Cruz de Elota) and one in Mexico City (Xochimilco). Fourteen isolates from leaves and roots were evaluated to assess: i) the ability to promote growth in chili pepper and tomato plants, ii) the degree of parasitism on nematode eggs and second-stage juveniles (J2), and iii) the nematostatic and nematicidal effect of their filtrates on the J2. In the trials, the three most effective endophytic fungal isolates were Chaetomium globosum (S1TH2), Echria macrotheca (S3RT2) and Stagonospora trichophoricola (XRC3). All three fungal isolates increased growth on chili pepper plants after application, but only two (S3RT2 and XRC3) did so on tomato plants. S1TH2 parasitized M. enterolobii eggs; S3RT2 and XRC3 eggs of N. aberrans s.l.; S3RT2 also parasitized M. incognita eggs and J2 of N. aberrans s.l. The S1TH2 filtrate was nematostatic for M. incognita and N. aberrans s.l., the XRC3 filtrate was nematostatic for N. aberrans s.l., and the S3RT2 filtrate was nematostatic and nematicidal for the J2 of N. aberrans s.l. The results obtained indicate that these isolates could be involved in natural regulation and biological control of root-knot nematodes.

Evaluation of two nematophagous fungi for the control of false root-knot nematode Nacobbus aberrans in pepper crops

Evaluation of two nematophagous fungi for the control of false root-knot nematode Nacobbus aberrans in pepper crops

Sustainable strategies for management of the "false root-knot nematode" Nacobbus spp.

The genus Nacobbus, known as the false root-knot nematode, is native to the American continent and comprises polyphagous species adapted to a wide range of climatic conditions. Alone or in combination with other biotic and abiotic factors, Nacobbus spp. can cause significant economic yield losses on main food crops such as potato, sugar beet, tomato, pepper and bean, in South and North America. Although the genus distribution is restricted to the American continent, it has quarantine importance and is subject to international legislation to prevent its spread to other regions, such as the European Union. The management of Nacobbus spp. remains unsatisfactory due to the lack of information related to different aspects of its life cycle, survival stages in the soil and in plant material, a rapid and reliable diagnostic method for its detection and the insufficient source of resistant plant genotypes. Due to the high toxicity of chemical nematicides, the search for alternatives has been intensified. Therefore, this review reports findings on the application of environmentally benign treatments to manage Nacobbus spp. Biological control strategies, such as the use of different organisms (mainly bacteria, fungi and entomopathogenic nematodes) and other eco-compatible approaches (such as metabolites, essential oils, plant extracts, phytohormones and amendments), either alone or as part of a combined control strategy, are discussed. Knowledge of potential sources of resistance for genetic improvement for crops susceptible to Nacobbus spp. are also reported. The sustainable strategies outlined here offer immediate benefits, not only to counter the pathogen, but also as good alternatives to improve crop health and growth.

“The false root-knot nematode: Modification of the root anatomy and alteration of the physiological performance in tomato plants”

This work relates the biological cycle of the plant-parasitic nematode Nacobbus aberrans and its impact on the morphology and physiology of tomato (Solanum lycopersicum L) plants. Tomato var. platense plants were grown in 10 L pots in a greenhouse using a previously sterilized substrate. Half of the plants were inoculated at the time of transplanting with 5000 eggs of the nematode (parasitized treatment) and the other half remained noninoculated (control). Histological sections performed 75 days after inoculation showed that the establishment of adult females of N. aberrans in roots caused a displacement of the xylem and phloem. This alteration induced a series of changes and symptoms in parasitized plants compared to control plants. Stomatic conductance, photosystem II efficiency, and CO2 fixation (net photosynthesis) showed significantly lower values in parasitized plants. Leaf chlorophyll content and soluble protein content were also reduced. Plants inoculated with the nematode showed a higher accumulation of osmoregulatory metabolites such as proline and sugars as well as malondialdehyde, an indicator of cell membrane damage. Results indicate that the symptoms and alterations caused by this phytoparasite are consistent with those of a plant subjected to water stress.

Arbuscular mycorrhizal fungi against the false root-knot nematode activity in Capsicum annuum: physiological responses in plants

ABSTRACT Nacobbus aberrans affects plants growth and development, and decreases the production of numerous horticultural crops. Several investigations have shown that symbiosis with arbuscular mycorrhizae can confer tolerance to pathogens through different action mechanisms, such as nutrient space competition and plant resistance induction. The aim of this study was to analyse the potential of three arbuscular mycorrhizal fungi (AMF): Rhizophagus intraradices B1, Rhizophagus intraradices A2 and Funneliformis mosseae in the control of N. aberrans, and to evaluate the physiological and biochemical responses to inoculation in pepper plants. The experiment was conducted under controlled conditions. Mycorrhization percentages, chlorophyll, carotenes, soluble proteins, proline, phenolic compounds, total and reducing sugar content, relative conductivity of root cell membranes and final nematode population were determined. The mycorrhization percentages were higher in plants parasitised by N. aberrans than in those not parasitised. The final population of nematodes was reduced in the presence of mycorrhizae. In the absence of AMF, parasitism by N. aberrans caused a decrease in the soluble proteins and chlorophyll content. The loss of functionality of infected roots in the plants induced water stress, reflected by the accumulation of proline, sugar and increased the relative conductivity of cell membranes. At the same time, as a product of pathogenesis, phenolic compounds accumulated. Inoculation with AMF decreased the proline, sugars, phenolic compounds content and relative conductivity. These results show the potential for the use of AMF in pepper production to reduce the population of N. aberrans, being the strain R. intraradices B1 as the most promising candidate.

In vitro nematicidal activity of natural and semisynthetic cadinenes from Heterotheca inuloides against the plant-parasitic nematode Nacobbus aberrans (Tylenchida: Pratylenchidae).

Nacobbus aberrans (Tylenchida: Pratylenchidae) is one of the main plant-parasitic nematodes species that affects crops in Mexico, generating substantial economic losses. Traditionally, the control of the nematodes is carried out using chemical products; however, research efforts are presently focused on the search for new methods for the control of this pest. Natural products derived from plants are an alternative for the control of populations of plant-parasitic nematodes. The genus Heterotheca (Asteraceae) is characterized by containing sesquiterpenes with cadinane skeleton, and some species of this genus exert nematicidal activity. We determined the effects of selected Heterotheca inuloides plant metabolites and some semisynthetic derivatives on the hatching of eggs isolated from the gelatinous matrix and infective second-stage juveniles (J2) of the false root-knot nematode N. aberrans using an in vitro experimental model. Among the evaluated compounds, nematodes were more susceptible to hydroxylated and quinone compounds, whereas the remaining compounds showed moderate or no activity. The presence of the hydroxyl group is essential for nematicidal potential, with changes at the hydroxyl group modifying the nematicidal activity. Flowers of Heterotheca inuloides contain bioactive compounds that showed nematicidal activity against N. aberrans. Here we report the nematicidal activities of cadinenes isolated from the flowers of H. inuloides and their semisynthetic derivatives against the false root-knot nematode N. aberrans. © 2018 Society of Chemical Industry.

Mycorrhization and grafting improve growth in the tomato and reduce the population of Nacobbus aberrans

Inoculation with mycorrhizal fungi and the use of rootstock that is tolerant or resistant to nematodes are two strategies that allow the nematode to be controlled, and plants to coexist with the pathogen. However, the two techniques have always been tested in isolation, when their positive effects are less compared to when they are able to act together. In the present work, two rootstocks combined with the mycorrhizal fungus Rizophagus intraradices were compared, with the aim of evaluating their behaviour on the growth of tomato plants in soils infested with N. aberrans, the false root-knot nematode. The experiment was set up in a completely randomised design with ten replications, in a 3 x 2 x 2 factorial scheme. The treatments consisted of a combination of three factors: a) plant composition: two rootstocks (Solanum lycopersicum var. cerasiform ‘Carolina’ and S. lycopersicum ‘Maxifort’), onto which the ‘Santa Clara’ tomato (S. lycopersicum) was grafted, and a non-grafted plant, considered the control, which was the same cultivar as the graft; b) mycorrhization: mycorrhizal or non-mycorrhizal roots; c) a substrate infested or not infested with N. aberrans. The plants grafted onto ‘Maxifort’ showed significantly greater growth for shoot dry weight, root fresh weight and stem diameter. The rootstock under test had a lower pathogen reproductive factor than did the ungrafted plant. Mycorrhization contributed to a reduction in the number of days until flowering, and a reduction in the final population of N. aberrans for the three plant compositions under test.

Pest categorisation of Nacobbusaberrans.

The Panel on Plant Health performed a pest categorisation of Nacobbus aberrans (Nematoda: Pratylenchidae), the false root‐knot nematode, for the EU. The nematode was originally described from the American continent. Due to differences in host range as well as molecular variability among populations, N. aberrans should be regarded as a species complex (N. aberrans sensu lato). All populations belonging to this species complex are pests of important host plants in the EU. N. aberrans had been detected indoors in the EU in the 1950s and 1960s but is no longer reported to be present in the EU. It is regulated by Council Directive 2000/29/EC, listed in Annex IAI as N. aberrans (Thorne) Thorne and Allen. Species within the N. aberrans complex are endoparasitic with migratory and sedentary stages. They are highly polyphagous attacking many plant species. They are also found in soil where they can survive dry conditions and freezing temperatures. Plants for planting and soil are potential pathways for this nematode. Climatic conditions in the EU are similar to those found in the countries where the pest is present. Hosts of the nematode from which high‐yield losses have been reported include potato, sugar beet, tomato and beans. The nematode only moves short distances (around 1m) but may be spread with plants and soil moving activities. Measures are available to inhibit EU entry via potatoes and soil as such but not all host plants are covered by current legislation. Entry of the nematode with plants and soil attached to plants for planting that are not regulated is therefore possible. N. aberrans does satisfy all the criteria that are within the remit of EFSA to assess to be regarded as a Union quarantine pest.

Histopathology of Andean Potato (Solanum tuberosum Andigenum group) varieties parasitized by the false root-knot nematode, Nacobbus aberrans.

Landraces of the Solanum tuberosum Andigenum group are abundant and diverse. They are a valuable genetic resource possessing resistance to pests, diseases, and environmental stresses. In the Andean region, populations of the false root-knot nematode Nacobbus aberrans became specialized to infect native potatoes, being one of the major limiting factors affecting this crop. A better understanding of the host plant-parasite interactions is important in order to select tolerant or resistant plants to be included in management programs. Despite the close of association of N. aberrans with potato, and the great diversity of the S. tuberosum Andigenum group, few histopathological studies have been conducted. The aim of this work was to analyze histological alterations induced by different Argentine populations of the nematode in naturally infested roots of four Andean potato varieties (Collareja, Negra Imilla, Ojo de Señorita and Colorada). All the varieties showed hyperplastic tissue in the central zone of galls, where syncytia developed in close association with the nematode female. Syncytia were composed of modified hyperplastic tissue and parenchyma xylem cells. The results showed differences among varieties in their response to nematode populations, with Ojo de Señorita and Negra Imilla being the most susceptible ones. This study is the first describing histopathological alterations induced by N. aberrans in susceptible Andean potato landraces.

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.

Histopathology of roots of three tomato cultivars infected with two separate isolates of the false root-knot nematode Nacobbus aberrans

The plant-parasitic nematode Nacobbus aberrans attacks weeds and cultivated plants, causing drastic crop yield losses. Several tomato cultivars, such as Superman and Mykonos, are produced by Seminis® as nematode resistant and are widely used in Argentina; their specific resistance response to different nematode species, however, is still unknown. In this study we explored the response of tomato cultivars to the infection of N. aberrans isolates, and determined the host status by performing histological analyses and estimating egg mass index (EMI). Two Argentina isolates (from Lules-Tucuman and Rio Cuarto-Cordoba) were tested separately in plants of Superman, Mykonos and Platense cultivars. Plants were maintained in a greenhouse for 90 days; then EMI was estimated in root systems and the material was processed to prepare histological slides and for histochemical test. Infected roots exhibited galls with females and a syncytium (feeding site) developed inside them. The vascular tissues were disorganized and displaced to the periphery; xylem percentage was lower than that in the control plants. All the cultivars were susceptible and developed a close plant-parasite relationship, with Mykonos and Platense cultivars infected with the Lules isolate being the most highly affected, as indicated by their highest EMI values. Superman was the least susceptible cultivar, as evidenced by its lowest EMI values, the amount of starch observed, the presence of thickened cell walls around the nematode and the egg mass, and the low percentage of gall occupied by syncytium.

Nematicidal Efficacy of Fluensulfone against False Root-knot Nematode (Nacobbus aberrans) in Cucumber Crop under Field Conditions

Nematicidal Efficacy of Fluensulfone against False Root-knot Nematode (Nacobbus aberrans) in Cucumber Crop under Field Conditions

Host suitability of peppers to the false root-knot nematode Nacobbus aberrans

The false root-knot nematode, Nacobbus aberrans, causes severe damage to field and greenhouse pepper crops in several localities of the American continent. No commercial peppers (Capsicum annuum) resistant to this nematode are available up to the present. Host suitability of 6 experimental and 3 commercial peppers (some of them carrying Me1 and Me7 resistance genes to Meloidogyne spp.) to two N. aberrans populations were evaluated under greenhouse experiments. None of the peppers was found to be resistant to the nematode. The evaluated parameters exhibited significant differences among some peppers tested within a single population and between populations for a single plant material. Some peppers carrying resistance showed higher nematode reproduction than some lines that did not possess resistance genes. These results confirmed that the genes conferring resistance to Meloidogyne spp. do not provide protection against this species of root-galling nematode. Host suitability of pepper lines carrying Me1 or Me7 resistance genes against N. aberrans is evaluated for the first time. Search for resistant genes against this nematode in wild peppers growing in areas where this nematode is indigenous should be promoted.

Use of the arbuscular mycorrhizal fungus Glomus intraradices as biological control agent of the nematode Nacobbus aberrans parasitizing tomato

ABSTRACT The plant-parasitic nematode Nacobbus aberrans is an endoparasite that induces gall formation in the roots and causes severe losses to diverse crops. Some populations of this nematode show preference for certain hosts, revealing the existence of “races/groups” with diff erent behaviour and making nematode management difficult. A possible biological control alternative to reduce the damage caused by this species may be the use of arbuscular mycorrhizal fungi (AMF). In the present work, the effect of Glomus intraradices on tomato plants inoculated with the nematode at transplanting and three weeks later was tested. At 60 days, the following parameters were estimated: percentage of AMF colonization, root and aerial dry weight, number of galls and egg masses, and reproduction factor (RF=final population/initial population) of N. aberrans . AMF colonization was higher in the presence of the nematode. The use of AMF favoured tomato biomass and reduced the number of galls and RF on the plants inoculated with the nematode at transplanting. Key words: arbuscular mycorrhiza, false root-knot nematode, microbiological control, plant protection

The transcriptome of Nacobbus aberrans reveals insights into the evolution of sedentary endoparasitism in plant-parasitic nematodes.

Within the phylum Nematoda, plant-parasitism is hypothesized to have arisen independently on at least four occasions. The most economically damaging plant-parasitic nematode species, and consequently the most widely studied, are those that feed as they migrate destructively through host roots causing necrotic lesions (migratory endoparasites) and those that modify host root tissue to create a nutrient sink from which they feed (sedentary endoparasites). The false root-knot nematode Nacobbus aberrans is the only known species to have both migratory endoparasitic and sedentary endoparasitic stages within its life cycle. Moreover, its sedentary stage appears to have characteristics of both the root-knot and the cyst nematodes. We present the first large-scale genetic resource of any false-root knot nematode species. We use RNAseq to describe relative abundance changes in all expressed genes across the life cycle to provide interesting insights into the biology of this nematode as it transitions between modes of parasitism. A multigene phylogenetic analysis of N. aberrans with respect to plant-parasitic nematodes of all groups confirms its proximity to both cyst and root-knot nematodes. We present a transcriptome-wide analysis of both lateral gene transfer events and the effector complement. Comparing parasitism genes of typical root-knot and cyst nematodes to those of N. aberrans has revealed interesting similarities. Importantly, genes that were believed to be either cyst nematode, or root-knot nematode, “specific” have both been identified in N. aberrans. Our results provide insights into the characteristics of a common ancestor and the evolution of sedentary endoparasitism of plants by nematodes.

Biological control of the false root-knot nematode Nacobbus aberrans by Pseudomonas protegens under controlled conditions

The use of antagonistic biological agents, such as fungi and bacteria, offers an economical and safe strategy to manage plant–parasitic nematodes in infested fields. The false root-knot nematode, Nacobbus aberrans, is a damaging parasite of many agronomic and horticultural crops in South and North America. The management of this nematode is challenging and often not profitable for farmers. In greenhouse tests, conducted in Argentina, applications of the strain Pseudomonas protegens CHA0 and its isogenic derivative ARQ1 (used as control) at a rate of 108 cfu ml−1 suppressed infection and reproduction of N. aberrans on tomato roots. However, neither of the strains promoted plant root or shoot growth of the treated plants. Root colonization by the bacteria was assessed by specific PCR–RFLP protocols and fluorescence microscopy. The results obtained in this preliminary study were encouraging and showed the potential of P. protegens CHA0 to be used for the management of the false root-knot nematode on tomato.

Tanscript accumulation of the mevalonate pathway genes and enzymatic activity of HMGCoA-r and EAS in chilli CM-334 infected by the false root-knot nematode Nacobbus aberrans

Chilli CM-334 (Capsicum annuum L.) is resistant to Phytophthora capsici Leonian, but susceptible to Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944. Its resistance to the oomycete breaks down when the plant is co-infected by this nematode. Transcript accumulation of 3-hydroxy-3-methylglutaryl CoA reductase (HMG1, HMG2 and HMG3 isoforms), farnesyl pyrophosphate synthase (FPPS), 5-epi-aristolochene synthase (EAS) and squalene synthase (SS) genes, as well as the enzymatic activities of HMGCoA-r and EAS in roots of chilli pepper CM-334 infected and non-infected by N. aberrans were determined. Plants were inoculated with 2,000 second stage juveniles of N. aberrans. Roots were harvested at 0, 2, 7, 14 and 21 days after inoculation (dai). At all of the evaluation times, there was a significantly greater accumulation of HMG1 transcripts in plants inoculated with N. aberrans than in non-inoculated plants. In contrast, HMG2 transcripts accumulated to a greater extent only at 7 dai. The largest accumulation of HMG1 mRNA was associated with a higher HMGCoAr activity and the presence of the immature females of the nematode inside the roots. The accumulation of EAS transcripts was also significantly greater in infected roots at all times after N. aberrans inoculation but its relationship to EAS enzymatic activity was not proportional. No changes in the accumulation of HMG3 and SS mRNAs were observed. FPPS mRNA levels increased in infected plants at 21 dai. The results suggest that N. aberrans modifies the expression of some genes of the mevalonate (MEV) pathway in order to create suitable conditions for its establishment and development.

The false root-knot nematode: A unique plant pathogen native to the Western Hemisphere

The false root-knot nematode: A unique plant pathogen native to the Western Hemisphere

Effect of the arbuscular mycorrhizal fungus Glomus intraradices on the false root-knot nematode Nacobbus aberrans in tomato plants

Information about the interaction between arbuscular mycorrhizal fungi (AMF) and the false root-knot nematode Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944 is scarce. The effect of Glomus intraradices Schenk & Smith on tomato (Lycopersicon esculentum L.) cv. Platense inoculated with nematode juveniles from Lisandro Olmos (Argentina) was studied under greenhouse conditions. Six treatments with five replications were performed. After 80 days, nematode reproduction and percentage of AMF colonization in roots were estimated. Some plant growth parameters were also measured. In general, plants with AMF and AMF plus nematodes grew as well as the control without AMF and without nematodes. Furthermore, G. intraradices was beneficial in reducing nematode-induced damage in roots (lower number of galls) as well as in having a suppressive effect on parasite reproduction. This is the first study on the use of G. intraradices as a possible strategy in the control of N. aberrans in tomato.

Speciation within Nacobbus: consilience or controversy?

AbstractAlthough Nacobbus aberrans, the false root-knot nematode, is endemic to the American continent, it justifies the attention granted by international quarantine regulations due to its broad host-range and economic importance in crops such as potato, tomato and sugarbeet. Until recently, it was widely accepted that the genus Nacobbus included only two valid species: N. aberrans and N. dorsalis. Traditionally, criteria to identify and separate the species have been based on morphology, host-range and some biological features. Molecular characterisation of populations can help to identify species that are otherwise almost impossible to segregate and has provided information that has identified aggregates of species or groups within the N. aberrans complex. This information needs to be integrated with knowledge already provided by non-molecular methodologies in order to establish a robust and workable framework that facilitates the assessment and assignment of nematode populations to an identifiable species, subspecies or group. The current molecular data indicate that the traditional two species paradigm is outdated and demand a re-assessment of the taxonomic status of the N. aberrans species complex. Whether molecular-based clades are recognised at specific rank or not, sequence analysis opens the door to reliable and incontrovertible diagnostics, a prerequisite for sustainable management practices and international quarantine regulations pertaining to the genus.