Nematode Nacobbus Aberrans Research Articles

Physiological acclimatization in a medium amended with colloidal chitin improves the nematophagous capacity of a fungus on the tomato root-knot nematode

Purpureocillium lilacinum is a nematophagous fungus whose ability to control the plant parasitic nematode Nacobbus aberrans sensu lato has been demonstrated. In this study, physiological acclimatization was performed using different nutrient sources and water activity levels of the culture medium to improve the nematophagous activity of two strains of P. lilacinum (SR14 and SR38). The development of the fungal inoculum in a medium amended with colloidal chitin and reduced levels of water activity (0.95) stimulates the production of conidia and pathogenicity in vitro. This condition was selected to produce the fungal inoculum for conducting antagonism studies against N. aberrans s.l. in tomato plants. The nematode population was significantly reduced (94–96%) with the application of SR38 and SR14 + SR38. The physiological acclimatization in medium with colloidal chitin and 0.95 water activity stimulates the pathogenicity mechanisms (sporulation and infectivity) of P. lilacinum SR38, improving its nematophagous capacity.

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

In vitro nematicidal and acaricidal effect of biosurfactants produced by Bacillus against the root-knot nematode Nacobbus aberrans and the dust mite Tyrophagus putrescentiae.

In the present study, the nematicidal and acaricidal activity of three biosurfactants (BS) produced by strains of the Bacillus genus was evaluated. The BS produced by the Bacillus ROSS2 strain presented a mortality of 39.29% in juveniles (J2) of Nacobbus aberrans at a concentration of 30 mg/mL, this same strain is the one that presented the highest mortality in Tyrophagus putrescentiae, which was 57.97% at a concentration of 39 mg/mL. The BS were qualitatively identified by thin layer chromatography and are lipid in nature based on the retention factor (Rf). While the GC-MS analysis identified two main compounds that are 4,7-Methano-1H-indene-2,6-dicarboxylic acid, 3a,4,7,7a-tetrahydro-1, and Methyl 4-(pyrrol-1-yl)-1,2,5-oxadiazole-3-carboxylate1, which is the polar part indicated by the presence of dicarboxylic acid and carboxylate groups; while the non-polar portion can be interpreted as a hydrocarbon chain of variable length. Based on the present results, BS can be an alternative for the biocontrol of the root-knot nematode N. aberrans and the mite T. putrescentiae.

Transcriptional alterations induced by Nacobbus aberrans in interaction with chili pepper CM-334 and Phytophthora capsici

The wilting of chili caused by Phytophthora capsici limits production of the crop. The best alternative for control of this disease is the use of crop resistance. The genotype of chili Criollo de Morelos 334 (CM-334) is resistant to P. capsici; however, its resistance is lost when it is infected by the nematode Nacobbus aberrans, a phenomenon known as breaking of resistance. With the objective of increasing knowledge about the transcriptional alterations of the defence genes associated with the resistance to the oomycete, we analyzed transcriptome in the roots of chili pepper CM-334 in response to infection by N. aberrans, by P. capsici and by the combination of both pathogens, at 12 and 24 h after inoculation with the oomycete (hpio). In plants inoculated only with P. capsici, this was detected in the neck of the plant at both of the times evaluated, whilst in plants inoculated with both pathogens, the oomycete was detected halfway up the stem at 24 hpio. Analysis of differential expression indicated that, in the plants inoculated with the oomycete, the genes PR-1b, PRB1, egl12, egl7, CPI, MIR, PGIP and CaWRKY58, could be involved in the defence of chili pepper CM-334 to P. capsici. PR-1b, CaWRKY58, CPI, MIR, HMG and PAL were modulated by N. aberrans. In addition, over-expression of gene FAD, involved in metabolism of lípids, was observed and this increase could help the nematode's requierements for fatty acids, which are essential for its development and reproduction. N. aberrans caused the transcriptional alteration of certain defence genes, which could have favoured the systemic advance of the oomycete halfway up the stem of CM-334.

Transcriptomic Analysis of the CM-334/P. capsici/N. aberrans Pathosystem to Identify Components in Plant Resistance and Resistance-Breaking Responses

Phytophthora capsici is an important pathogen worldwide because its spread affects pepper production globally. The “Criollo de Morelos” pepper 334 (CM-334) is resistant to P. capsici strains, regardless of the aggressiveness of the strain or the environmental conditions. However, when the nematode Nacobbus aberrans infects peppers, they lose this resistance by a process defined as “Resistance-breaking”. Breakdown of resistance results from a transcriptomic reconfiguration of the pepper that induces some defense genes, such as WRKY-a, POX, and EAS. The interest in identifying and describing the resistance process to P. capsici, and the breakdown that occurs by N. aberrans, has allowed us to establish a model in which we can analyze the modulation process in both scenarios and identify this transcriptomic modulation. The objective of the present work is to carry out a transcriptomic analysis that demonstrates the modulation of resistance and resistance-breaking processes. It would allow us to identify relevant genes in the early (12 h) and late (24 h) stages in these processes of the CM-334 pepper. Our findings demonstrate that modulation of resistance and resistance-breaking are independent processes that depend on the presence of both pathogens (P. capsici and N. aberrans) and that their timing modulation is dynamic.

“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.

Decrypting species in the Nacobbus aberrans (Nematoda: Pratylenchidae) complex using integrative taxonomy

AbstractThe plant‐parasitic nematode Nacobbus aberrans s.l. is a major agricultural pest of quarantine importance worldwide and is one of the top 10 nematodes in plant pathology because it causes significant losses in several crops. There are evidences of the existence of a species complex, with species being difficult to discriminate using only morphological characters. In this study, we aimed at resolving the taxonomic situation from a multi‐disciplinary approach, based on morphometric data and molecular analyses. The results supported the identification of three nominal species in the complex: N. aberrans s.s., N. bolivianus and a new taxon, Nacobbus celatus sp. n. This new species, described based on the revision of published and new data, is widely distributed in the lowlands of Argentina. Our results also evidence the possible existence of a new taxon native to the Andean region of the same country. For the first time, the utility of cytochrome oxidase c subunit 1 barcoding for Nacobbus species identification is corroborated. This study also includes the estimation of divergence time among Nacobbus spp.; the possible geographical origin of the genus and colonization pattern are discussed. The present work shows the usefulness of an integrated approach to the resolution of systematic problems.

In vitro compatibility of Pimpinella anisum and Origanum vulgare essential oils with nematophagous fungi and their effects against Nacobbus aberrans

The soil nematode Nacobbus aberrans (Thorne & Allen) is one of the recurrent biotic adversities in crops growing under cover, and its presence in the horticultural area of Rio Cuarto, Argentina, is reported from the 1980s to the present day. The use of botanical extracts in combination with biological control agents could be a promising method for the control of this nematode. Nematicidal effects of Pimpinella anisum (anise) and Origanum vulgare (oregano) essential oils (EOs) against second-stage juveniles (J2) of N. aberrans were evaluated in vitro. Fisher LSD tests evidenced significant nematicidal (α = 0.05) effects of the two EOs tested, with LD100 of 200 and 600 µL L−1 for anise and oregano, respectively. Compatibility assays between EOs and five nematophagous fungi were microscopically and macroscopically performed on soil extract solid medium (SESM) conditioned at different water activities (0.99 and 0.98 aw) and incubated at 30, 25 and 20 °C. Purpureocillium lilacinum SR14 was the fungal strain that showed compatibility at levels of spore germination, viability of propagules and growth rate under the different anise oil doses, temperatures and aw assayed. In conclusion, the integrated application of anise EO with the nematophagous fungus, which combines two action mechanisms, could generate, on the one hand, a rapid larval mortality effect caused by the EO and, on the other hand, a parasitic effect that has the advantage of remaining in time under variable environmental conditions.

Strengthening mycorrhizal research in South America.

Strengthening mycorrhizal research in South America.

Screening and identification of horticultural soil fungi for their evaluation against the plant parasitic nematode Nacobbus aberrans.

The plant-parasitic nematode Nacobbus aberrans is an endoparasite causing severe losses to a wide range of crops from North to South America. The use of native antagonistic fungi may be considered as a possible biological control alternative to reduce the damages caused by this species. Antagonistic effects of 66 potential nematophagous fungi against eggs (J1) and second-stage juveniles (J2) of N. aberrans, were evaluated in vitro on water agar. DGC test showed significant differences (p < 0.0001) in the efficacy of some fungal isolates tested, with parasitism levels for J1 and J2 of 0-95 and 1-78%, respectively. Five isolates of Purpureocillium lilacinum, Metarhizium robertsii and Plectosphaerella plurivora appeared as the most effective antagonists of N. aberrans, relying on hyphae and adhesive conidia in host infection processes.

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.

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.

Phylogenetic relationships among populations of the Nacobbus aberrans (Nematoda, Pratylenchidae) complex reveal the existence of cryptic species

The plant‐parasitic nematode Nacobbus aberrans sensu lato is an agricultural pest of quarantine importance. Due to the morphometric, physiological and genetic variability observed within the species, there is no agreement on the taxonomy of this nematode. The objective of this study was to analyse the ITS rDNA region and the D2–D3 expansion segments of 28S rDNA in 10 Argentine populations and one from Ecuador and to establish their phylogenetic relationship with other known sequences from South and North America. Phylogenetic trees of the ITS gene showed seven statistically well‐supported clades; the high and significant Fst values obtained among these groups confirmed this partitioning. The Argentine populations here considered were separated into three clades: one comprising a population from the Andean region and two grouping nematodes from lower altitudes. Three other clades were distinguished for South American populations, which included known sequences of individuals from Peru, Bolivia and north of Argentina. The other clade included sequences from Mexico, Ecuador and two Argentine populations of unknown origin. The important degree of genetic divergence observed among Andean populations suggests that the Andes may have played a crucial role in speciation of Nacobbus, which would have originated in this region. Although D2–D3 segments exhibited lower variation, they were useful for establishing phylogenetic relationships among the Argentine populations considered in this work. As there are no other GenBank sequences available for these segments, it was not possible to make comparisons with other populations from South and North America. The considerable genetic differentiation observed in ITS rDNA region among Nacobbus populations showed evidence of cryptic species within the N. aberrans s.l. complex. Integration of morphological and morphometric studies and molecular analyses considering other genes may aid in the identification of species and their phylogenetic relationships within this genus.

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.