Showing papers on "Meloidogyne incognita published in 2016"

Bacillus cereus strain S2 shows high nematicidal activity against Meloidogyne incognita by producing sphingosine

Abstract: Plant-parasitic nematodes cause serious crop losses worldwidely. This study intended to discover the antagonistic mechanism of Bacillus cereus strain S2 against Meloidogyne incognita. Treatment with B. cereus strain S2 resulted in a mortality of 77.89% to Caenorhabditis elegans (a model organism) and 90.96% to M. incognita. In pot experiment, control efficiency of B. cereus S2 culture or supernatants were 81.36% and 67.42% towards M. incognita, respectively. In field experiment, control efficiency was 58.97% towards M. incognita. Nematicidal substances were isolated from culture supernatant of B. cereus S2 by polarity gradient extraction, silica gel column chromatography and HPLC. Two nematicidal compounds were identified as C16 sphingosine and phytosphingosine by LC-MS. The median lethal concentration of sphingosine was determined as 0.64 μg/ml. Sphingosine could obviously inhibit reproduction of C. elegans, with an inhibition rate of 42.72% for 24 h. After treatment with sphingosine, ROS was induced in intestinal tract, and genital area disappeared in nematode. Furthermore, B. cereus S2 could induce systemic resistance in tomato, and enhance activity of defense-related enzymes for biocontrol of M. incognita. This study demonstrates the nematicidal activity of B. cereus and its product sphingosine, as well provides a possibility for biocontrol of M. incognita.

Msp40 effector of root-knot nematode manipulates plant immunity to facilitate parasitism.

Abstract: Root-knot nematodes (RKNs) are obligate biotrophic parasites that invade plant roots and engage in prolonged and intimate relationships with their hosts. Nematode secretions, some of which have immunosuppressing activity, play essential roles in successful parasitism; however, their mechanisms of action remain largely unknown. Here, we show that the RKN-specific gene MiMsp40, cloned from Meloidogyne incognita, is expressed exclusively in subventral oesophageal gland cells and is strongly upregulated during early parasitic stages. Arabidopsis plants overexpressing MiMsp40 were more susceptible to nematode infection than were wild type plants. Conversely, the host-derived MiMsp40 RNAi suppressed nematode parasitism and/or reproduction. Moreover, overexpression of MiMsp40 in plants suppressed the deposition of callose and the expression of marker genes for bacterial elicitor elf18-triggered immunity. Transient expression of MiMsp40 prevented Bax-triggered defence-related programmed cell death. Co-agroinfiltration assays indicated that MiMsp40 also suppressed macroscopic cell death triggered by MAPK cascades or by the ETI cognate elicitors R3a/Avr3a. Together, these results demonstrate that MiMsp40 is a novel Meloidogyne-specific effector that is injected into plant cells by early parasitic stages of the nematode and that plays a role in suppressing PTI and/or ETI signals to facilitate RKN parasitism.

A novel serine protease, Sep1, from Bacillus firmus DS-1 has nematicidal activity and degrades multiple intestinal-associated nematode proteins.

Abstract: Plant-parasitic nematodes (PPNs) cause serious harm to agricultural production. Bacillus firmus shows excellent control of PPNs and has been produced as a commercial nematicide. However, its nematicidal factors and mechanisms are still unknown. In this study, we showed that B. firmus strain DS-1 has high toxicity against Meloidogyne incognita and soybean cyst nematode. We sequenced the whole genome of DS-1 and identified multiple potential virulence factors. We then focused on a peptidase S8 superfamily protein called Sep1 and demonstrated that it had toxicity against the nematodes Caenorhabditis elegans and M. incognita. The Sep1 protein exhibited serine protease activity and degraded the intestinal tissues of nematodes. Thus, the Sep1 protease of B. firmus is a novel biocontrol factor with activity against a root-knot nematode. We then used C. elegans as a model to elucidate the nematicidal mechanism of Sep1 and the results showed that Sep1 could degrade multiple intestinal and cuticle-associated proteins and destroyed host physical barriers. The knowledge gained in our study will lead to a better understanding of the mechanisms of B. firmus against PPNs and will aid in the development of novel bio-agents with increased efficacy for controlling PPNs.

Effects of Tomato Root Exudates on Meloidogyne incognita

Abstract: Plant root exudates affect root-knot nematodes egg hatch. Chemicals in root exudates can attract nematodes to the roots or result in repellence, motility inhibition or even death. However, until recently little was known about the relationship between tomato root exudates chemicals and root-knot nematodes. In this study, root exudates were extracted from three tomato rootstocks with varying levels of nematode resistance: Baliya (highly resistant, HR), RS2 (moderately resistant, MR) and L-402 (highly susceptible, T). The effects of the root exudates on Meloidogyne incognita (M. incognita) egg hatch, survival and chemotaxis of second-stage juveniles (J2) were explored. The composition of the root exudates was analysed by gas chromatography/mass spectrometry (GC/MS) prior to and following M. incognita inoculation. Four compounds in root exudates were selected for further analysis and their allopathic effect on M. incognita were investigated. Root exudates from each tomato rootstocks (HR, MR and T strains) suppressed M. incognita egg hatch and increased J2 mortality, with the highest rate being observed in the exudates from the HR plants. Exudate from HR variety also repelled M. incognita J2 while that of the susceptible plant, T, was demonstrated to be attractive. The relative amount of esters and phenol compounds in root exudates from HR and MR tomato rootstocks increased notably after inoculation. Four compounds, 2,6-Di-tert-butyl-p-cresol, L-ascorbyl 2,6-dipalmitate, dibutyl phthalate and dimethyl phthalate increased significantly after inoculation. The egg hatch of M. incognita was suppressed by each of the compound. L-ascorbyl 2,6-dipalmitate showed the most notable effect in a concentration-dependent manner. All four compounds were associated with increased J2 mortality. The greatest effect was observed with dimethyl phthalate at 2 mmol·L-1. Dibutyl phthalate was the only compound observed to repel M. incognita J2 with no effect being detected in the other compounds. Each of the four compounds were correlated with a reduction in disease index in the susceptible cultivar, T, and tomato seedlings irrigated with L-ascorbyl 2,6-dipalmitate at 2 mmol·L-1 showed the best resistance to M. incognita. Taken together, this study provided a valuable contribution to understanding the underlying mechanism of nematode resistance in tomato cultivars.

Biological Control of Meloidogyne incognita by Aspergillus niger F22 Producing Oxalic Acid.

Abstract: Restricted usage of chemical nematicides has led to development of environmentally safe alternatives. A culture filtrate of Aspergillus niger F22 was highly active against Meloidogyne incognita with marked mortality of second-stage juveniles (J2s) and inhibition of egg hatching. The nematicidal component was identified as oxalic acid by organic acid analysis and gas chromatography-mass spectroscopy (GC-MS). Exposure to 2 mmol/L oxalic acid resulted in 100% juvenile mortality at 1 day after treatment and suppressed egg hatching by 95.6% at 7 days after treatment. Oxalic acid showed similar nematicidal activity against M. hapla, but was not highly toxic to Bursaphelenchus xylophilus. The fungus was incubated on solid medium and dried culture was used for preparation of a wettable powder-type (WP) formulation as an active ingredient. Two WP formulations, F22-WP10 (ai 10%) and oxalic acid-WP8 (ai 8%), were prepared using F22 solid culture and oxalic acid. In a field naturally infested with M. incognita, application of a mixture of F22-WP10 + oxalic acid-WP8 at 1,000- and 500-fold dilutions significantly reduced gall formation on the roots of watermelon plants by 58.8 and 70.7%, respectively, compared to the non-treated control. The disease control efficacy of the mixture of F22-WP10 + oxalic acid-WP8 was significantly higher than that of a chemical nematicide, Sunchungtan (ai 30% fosthiazate). These results suggest that A. niger F22 can be used as a microbial nematicide for the control of root-knot nematode disease.

A Novel Meloidogyne incognita Effector Misp12 Suppresses Plant Defense Response at Latter Stages of Nematode Parasitism.

Abstract: Secreted effectors in plant root-knot nematodes (RKNs, or Meloidogyne spp.) play key roles in their parasite processes. Currently identified effectors mainly focus on the early stage of the nematode parasitism. There are only a few reports describing effectors that function in the latter stage. In this study, we identified a potential RKN effector gene, Misp12, that functioned during the latter stage of parasitism. Misp12 was unique in the Meloidogyne spp., and highly conserved in Meloidogyne incognita. It encoded a secretory protein that specifically expressed in the dorsal esophageal gland, and highly up-regulated during the female stages. Transient expression of Misp12-GUS-GFP in onion epidermal cell showed that Misp12 was localized in cytoplast. In addition, in planta RNA interference targeting Misp12 suppressed the expression of Misp12 in nematodes and attenuated parasitic ability of M. incognita. Furthermore, up-regulation of jasmonic acid (JA) and salicylic acid (SA) pathway defense-related genes in the virus-induced silencing of Misp12 plants, and down-regulation of SA pathway defense-related genes in Misp12-expressing plants indicated the gene might be associated with the suppression of the plant defense response. These results demonstrated that the novel nematode effector Misp12 played a critical role at latter parasitism of M. incognita.

Expression of a Cystatin Transgene in Eggplant Provides Resistance to Root-knot Nematode, Meloidogyne incognita.

Abstract: Root-knot nematodes (RKN) cause substantial yield decline in eggplant and sustainable management options to minimize crop damage due to nematodes are still limited. A number of genetic engineering strategies have been developed to disrupt the successful plant-nematode interactions. Among them, delivery of proteinase inhibitors from the plant to perturb nematode development and reproduction is arguably the most effective strategy. In the present study, transgenic eggplant expressing a modified rice cystatin (OC-IΔD86) gene under the control of the root-specific promoter, TUB-1, was generated to evaluate the genetically modified nematode resistance. Five putative transformants were selected through PCR and genomic Southern blot analysis. Expression of the cystatin transgene was confirmed in all the events using western blotting, ELISA and qPCR assay. Upon challenge inoculation, all the transgenic events exhibited a detrimental effect on RKN development and reproduction. The best transgenic line (a single copy event) showed 78.3% inhibition in reproductive success of RKN. Our results suggest that cystatins can play an important role for improving nematode resistance in eggplant and their deployment in gene pyramiding strategies with other proteinase inhibitors could ultimately enhance crop yield.

Untargeted Metabolomics of Tomato Plants after Root-Knot Nematode Infestation.

Abstract: After 2 months from the infestation of tomato plants with the root-knot nematode (RKN) Meloidogyne incognita, we performed a gas chromatography–mass spectrometry untargeted fingerprint analysis for the identification of characteristic metabolites and biomarkers. Principal component analysis, and orthogonal projections to latent structures discriminant analysis suggested dramatic local changes of the plant metabolome. In the case of tomato leaves, β-alanine, phenylalanine, and melibiose were induced in response to RKN stimuli, while ribose, glycerol, myristic acid, and palmitic acid were reduced. For tomato stems, upregulated metabolites were ribose, sucrose, fructose, and glucose, while fumaric acid and glycine were downregulated. The variation in molecular strategies to the infestation of RKNs may play an important role in how Solanum lycopersicum and other plants adapt to nematode parasitic stress.

Assessment of DAPG-producing Pseudomonas fluorescens for Management of Meloidogyne incognita and Fusarium oxysporum on Watermelon

Abstract: Pseudomonas fluorescens isolates Clinto 1R, Wayne 1R, and Wood 1R, which produce the antibiotic 2,4-diacetylphloroglucinol (DAPG), can suppress soilborne diseases and promote plant growth. Consequently, these beneficial bacterial isolates were tested on watermelon plants for suppression of Meloidogyne incognita (root-knot nematode: RKN) and Fusarium oxysporum f. sp. niveum (Fon). In a greenhouse trial,Wayne 1R root dip suppressed numbers of RKN eggs per gram root on ‘Charleston Gray’ watermelon by 28.9%. However, in studies focused on ‘Sugar Baby’ watermelon, which is commercially grown in Maryland, a Wayne 1R root dip did not inhibit RKN reproduction or plant death caused by Fon. When all three isolates were applied as seed coats, plant stand in the greenhouse was reduced up to 60% in treatments that included Fon 6 P. fluorescens, and eggs per gram root did not differ among treatments. In a microplot trial with Clinto 1R and Wayne 1R root dips, inoculation with P. fluorescens and/or Fon resulted in shorter vine lengths than treatment with either P. fluorescens isolate plus RKN. Root weights, galling indices, eggs per gram root, and second-stage juvenile (J2) numbers in soil were similar among all RKN-inoculated treatments, and fruit production was not affected by treatment. Plant death was high in all treatments. These studies demonstrated that the tested P. fluorescens isolates resulted in some inhibition of vine growth in the field, and were not effective for enhancing plant vigor or suppressing RKN or Fon on watermelon.

Advancements in breeding, genetics, and genomics for resistance to three nematode species in soybean

Abstract: Integration of genetic analysis, molecular biology, and genomic approaches drastically enhanced our understanding of genetic control of nematode resistance and provided effective breeding strategies in soybeans Three nematode species, including soybean cyst (SCN, Heterodera glycine), root-knot (RKN, Meloidogyne incognita), and reniform (RN, Rotylenchulus reniformis), are the most destructive pests and have spread to soybean growing areas worldwide Host plant resistance has played an important role in their control This review focuses on genetic, genomic studies, and breeding efforts over the past two decades to identify and improve host resistance to these three nematode species Advancements in genetics, genomics, and bioinformatics have improved our understanding of the molecular and genetic mechanisms of nematode resistance and enabled researchers to generate large-scale genomic resources and marker-trait associations Whole-genome resequencing, genotyping-by-sequencing, genome-wide association studies, and haplotype analyses have been employed to map and dissect genomic locations for nematode resistance Recently, two major SCN-resistant loci, Rhg1 and Rhg4, were cloned and other novel resistance quantitative trait loci (QTL) have been discovered Based on these discoveries, gene-specific DNA markers have been developed for both Rhg1 and Rhg4 loci, which were useful for marker-assisted selection With RKN resistance QTL being mapped, candidate genes responsible for RKN resistance were identified, leading to the development of functional single nucleotide polymorphism markers So far, three resistances QTL have been genetically mapped for RN resistance With nematode species overcoming the host plant resistance, continuous efforts in the identification and deployment of new resistance genes are required to support the development of soybean cultivars with multiple and durable resistance to these pests

Fungal root endophytes of tomato from Kenya and their nematode biocontrol potential

Abstract: The significance of fungal endophytes in African agriculture, particularly Kenya, has not been well investigated. Therefore, the objective of the present work was isolation, multi-gene phylogenetic characterization and biocontrol assessment of endophytic fungi harbored in tomato roots for nematode infection management. A survey was conducted in five different counties along the central and coastal regions of Kenya to determine the culturable endophytic mycobiota. A total of 76 fungal isolates were obtained and characterized into 40 operational taxonomic units based on the analysis of ITS, β-tubulin and tef1α gene sequence data. Among the fungal isolates recovered, the most prevalent species associated with tomato roots were members of the Fusarium oxysporum and F. solani species complexes. Of the three genes utilized for endophyte characterization, tef1α provided the best resolution. A combination of ITS, β-tubulin and tef1α resulted in a better resolution as compared to single gene analysis. Biotests demonstrated the ability of selected non-pathogenic fungal isolates to successfully reduce nematode penetration and subsequent galling as well as reproduction of the root-knot nematode Meloidogyne incognita. Most Trichoderma asperellum and F. oxysporum species complex isolates reduced root-knot nematode egg densities by 35–46 % as compared to the non-fungal control and other isolates. This study provides first insights into the culturable endophytic mycobiota of tomato roots in Kenya and the potential of some isolates for use against the root-knot nematode M. incognita. The data can serve as a framework for fingerprinting potential beneficial endophytic fungal isolates which are optimized for abiotic and biotic environments and are useful in biocontrol strategies against nematode pests in Kenyan tomato cultivars. This information would therefore provide an alternative or complementary crop protection component.

Identification of Nematicidal Constituents of Notopterygium incisum Rhizomes against Bursaphelenchus xylophilus and Meloidogyne incognita.

Abstract: During a screening program for new agrochemicals from Chinese medicinal herbs, the ethanol extract of Notopterygium incisum rhizomes was found to possess strong nematicidal activity against the two species of nematodes, Bursaphelenchus xylophilus and Meloidogyne incognita. Based on bioactivity-guided fractionation, the four constituents were isolated from the ethanol extract and identified as columbianetin, falcarindiol, falcarinol, and isoimperatorin. Among the four isolated constituents, two acetylenic compounds, falcarindiol and falcarinol (2.20–12.60 μg/mL and 1.06–4.96 μg/mL, respectively) exhibited stronger nematicidal activity than two furanocoumarins, columbianetin, and isoimperatorin (21.83–103.44 μg/mL and 17.21–30.91 μg/mL, respectively) against the two species of nematodes, B. xylophilus and M. incognita. The four isolated constituents also displayed phototoxic activity against the nematodes. The results indicate that the ethanol extract of N. incisum and its four isolated constituents have potential for development into natural nematicides for control of plant-parasitic nematodes.

REPRODUCTION OF Meloidogyne incognita ON RESISTANT AND SUSCEPTIBLE OKRA CULTIVARS

Abstract: Root-knot nematodes are considered among the top five major plant pathogens and the first among the ten most important genera of plant parasitic nematodes in the world (Mukhtar et al., 2013a). They attack different crop plants including vegetables causing severe growth retardation due to formation of typical galls. They have been found implicated with other plant pathogens like Ralstonia solanacearum in aggravating wilt diseases (Iqbal and Mukhtar, 2014; Iqbal et al., 2014; Aslam et al., 2015; Shahbaz et al., 2015). In Pakistan Meloidogyne incognita is the dominant species and found throughout the okra-producing regions where it substantially affects growth and yield (Hussain et al., 2012; 2015). Sikora and Fernandez (2005) reported severe attack of root-knot disease caused by Meloidogyne spp. on okra and yield losses up to 27%. The yield losses caused by root-knot nematodes are due to buildup of inoculum of this pathogen (Kayani et al., 2013) and continuous growing of similar okra varieties in the same field year after year (Hussain et al., 2011a; 2014). Use of resistant cultivars and nematicides are the main strategies to abate yield losses caused by this nematode. Application of nematicides, though very effective, is not attractive to farming community due to their high costs and hazardous effects. Contrariwise, use of cultivars resistant to nematodes is environmentally benign, secure, innocuous and economically feasible means of controlling root-knot nematodes (Mukhtar et al., 2013b). Resistant cultivars can also be employed as a component of integrated nematode management along with other control strategies like organic soil amendments (Hussain et al., 2011b; Kayani et al., 2012), biocontrol (Mukhtar et al., 2013c), soil solarization, heat treatment, and crop rotation with non-hosts for controlling root-knot nematodes. Screening of crop plants for resistance to root-knot nematodes on the basis of galling index scale as a sole criterion of plant damage is not reliable. This emphasizes the need to include reproduction of nematodes on cultivars as necessary parameters in addition to root galling for evaluating crop cultivars as resistance, susceptible or tolerant (Florini,1997; Afolami, 2000). The main criteria for successful and acceptable use of cultivars in cropping systems are their capability to reduce subsequent nematode populations and to yield profitably in the presence of nematode pathogen. However, there is no information on the reproduction rates of M. incognita on okra cultivars widely grown in the country. For their suitability as nematode-suppressive crops in practice, it is essential that the rates of reproduction and development of M. incognita on these cultivars are compared. In the present study, we investigated the reproduction rates of M. incognita on twelve okra cultivars with varying levels of resistance or susceptibility in greenhouse experiments. Pak. J. Agri. Sci., Vol. 53(2), 371-375; 2016 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/16.4175 http://www.pakjas.com.pk

Potent Nematicidal Activity of Maleimide Derivatives on Meloidogyne incognita.

Abstract: Different maleimide derivatives were synthesized and assayed for their in vitro activity on the soil inhabiting, plant-parasitic nematode Meloidogyne incognita, also known as root-knot nematode. The compounds maleimide, N-ethylmaleimide, N-isopropylmaleimide, and N-isobutylmaleimide showed the strongest nematicidal activity on the second stage juveniles of the root-knot nematode with EC50/72h values of 2.6 ± 1.3, 5.1 ± 3.4, 16.2 ± 5.4, and 19.0 ± 9.0 mg/L, respectively. We also determined the nematicidal activity of copper sulfate, finding an EC50 value of 48.6 ± 29.8 mg/L. When maleimide at 1 mg/L was tested in combination with copper sulfate at 50 mg/L, we observed 100% mortality of the nematodes. We performed a GC-MS metabolomics analysis after treating nematodes with maleimide at 8 mg/L for 24 h. This analysis revealed altered fatty acids and diglyceride metabolites such as oleic acid, palmitic acid, and 1-monopalmitin. Our results suggest that maleimide may be used as a new interesting building block...

Effectiveness of Silver Nano-particles of Extracts of Urtica urens (Urticaceae) Against Root-knot Nematode Meloidogyne incognita

Abstract: Natural products are an important resource for finding new pesticides. Additionally, preparation of elemental nano-particles of natural products was proven to be promising as anti-microbial agents. Present study aimed to examine the petroleum ether, ethyl acetate and ethanol extracts of Urtica urens and their silver-nano formulations as nematicides against root-knot nematode Meloidogyne incognita. Leaf extracts of U. urens were prepared through successive extraction and the Ag-nanoparticles of extracts and the reference nematicide (rugby®) were synthesized. Results revealed that Ag-nano formulations of extracts were effective in the management of M. incognita. There was an 11-fold of activity between Ag-rugby and the least toxic extract (ethyl acetate) against eggs. The LC50 values showed significant effects of Ag-rugby, rugby® and Ag-petroleum ether against the larvae compared with petroleum ether, ethanol and ethyl acetate extracts. Petroleum ether extract and its Ag nano-particles might be considered as environmental-safe and effective nematicides alternatives against the invasive M. incognita.

Fine mapping and identification of candidate genes for a QTL affecting Meloidogyne incognita reproduction in Upland cotton

Abstract: The southern root-knot nematode (Meloidogyne incognita; RKN) is one of the most important economic pests of Upland cotton (Gossypium hirsutum L.). Host plant resistance, the ability of a plant to suppress nematode reproduction, is the most economical, practical, and environmentally sound method to provide protection against this subterranean pest. The resistant line Auburn 623RNR and a number of elite breeding lines derived from it remain the most important source of root-knot nematode (RKN) resistance. Prior genetic analysis has identified two epistatically interacting RKN resistance QTLs, qMi-C11 and qMi-C14, affecting gall formation and RKN reproduction, respectively. We developed a genetic population segregating only for the qMi-C14 locus and evaluated the genetic effects of this QTL on RKN resistance in the absence of the qMi-C11 locus. The qMi-C14 locus had a LOD score of 12 and accounted for 24.5 % of total phenotypic variation for egg production. In addition to not being significantly associated with gall formation, this locus had a lower main effect on RKN reproduction than found in our previous study, which lends further support to evidence of epistasis with qMi-C11 in imparting RKN resistance in the Auburn 623RNR source. The locus qMi-C14 was fine-mapped with the addition of 16 newly developed markers. By using the reference genome sequence of G. raimondii, we identified 20 candidate genes encoding disease resistance protein homologs in the newly defined 2.3 Mb region flanked by two SSR markers. Resequencing of an RKN resistant and susceptible G. hirsutum germplasm revealed non-synonymous mutations in only four of the coding regions of candidate genes, and these four genes are consequently of high interest. Our mapping results validated the effects of the qMi-C14 resistance locus, delimiting the QTL to a smaller region, and identified tightly linked SSR markers to improve the efficiency of marker-assisted selection. The candidate genes identified warrant functional studies that will help in identifying and characterizing the actual qMi-C14 defense gene(s) against root-knot nematodes.

Analysis of root-knot nematode and fusarium wilt disease resistance in cotton (Gossypium spp.) using chromosome substitution lines from two alien species

Abstract: Chromosome substitution (CS) lines in plants are a powerful genetic resource for analyzing the contribution of chromosome segments to phenotypic variance. In this study, a series of interspecific cotton (Gossypium spp.) CS lines were used to identify a new germplasm resource, and to validate chromosomal regions and favorable alleles associated with nematode or fungal disease resistance traits. The CS lines were developed in the G. hirsutum L. TM-1 background with chromosome or chromosome segment substitutions from G. barbadense L. Pima 3-79 or G. tomentosum. Root-knot nematode (Meloidogyne incognita) and fusarium wilt (Fusarium oxysporum f. sp. vasinfectum) (races 1 and 4) resistance alleles and quantitative trait loci (QTL) previously placed on cotton chromosomes using SSR markers in two interspecific recombinant inbred line populations were chosen for testing. Phenotypic responses of increased resistance or susceptibility in controlled inoculation and infested field assays confirmed the resistance QTLs, based on substitution with the positive or negative allele for resistance. Lines CS-B22Lo, CS-B04, and CS-B18 showed high resistance to nematode root-galling, confirming QTLs on chromosomes 4 and 22 (long arm) with resistance alleles from Pima 3-79. Line CS-B16 had less fusarium race 1-induced vascular root staining and higher percent survival than the TM-1 parent, confirming a major resistance QTL on chromosome 16. Lines CS-B(17-11) and CS-B17 had high fusarium race 4 vascular symptoms and low survival due to susceptible alleles introgressed from Pima 3-79, confirming the localization on chromosome 17 of an identified QTL with resistance alleles from TM1 and other resistant lines. Analyses validated regions on chromosomes 11, 16, and 17 harboring nematode and fusarium wilt resistance genes and demonstrated the value of CS lines as both a germplasm resource for breeding programs and as a powerful genetic analysis tool for determining QTL effects for disease resistance. CS lines carrying small alien chromosome segments with favorable QTL alleles could be used for effective introgression of biotic stress resistance or many other desirable traits by targeting gene interactions and reducing linkage drag effects.

RNAi-induced silencing of an effector confers transcriptional oscillation in another group of effectors in the root-knot nematode, Meloidogyne incognita

Abstract: The sophisticated parasitic tactic of sedentary endoparasitic nematodes seems to involve the simultaneous alteration of the expression of multitude of its effector genes in order to hijack the plant metabolic and developmental pathway. In concordance with this hypothesis, we have targeted some candidate effector genes of Meloidogyne incognita to understand the possible interaction among those effectors for successful infection of the host plant. In vitro RNAi strategy was used to knock down M. incognita -specific pioneer effector genes, such as msp-18 , msp-20 , msp-24 , msp-33 and msp-16 (known to interact with plant transcription factor), to investigate their possible effect on the expression of key cell wall-degrading enzymes (CWDE) and vice versa . Supported by the phenotypic data, intriguingly our study revealed that induced suppression of these pioneer genes cause transcriptional alteration of CWDE genes in M. incognita . This remarkable finding may provide some useful links for future research on nematode effector interaction.

Evaluation of entomopathogenic nematodes and the supernatants of the in vitro culture medium of their mutualistic bacteria for the control of the root-knot nematodes Meloidogyne incognita and M. arenaria

Abstract: BACKGROUND The suppressive effects of various formulations of four entomopathogenic nematode (EPN) species and the supernatants of their mutualistic bacteria on the root-knot nematodes (RKNs) Meloidogyne incognita and M. arenaria in tomato roots were evaluated. The EPNs Steinernema carpocapsae, S. feltiae, S. glaseri and Heterorhabditis bacteriophora were applied as either live infective juveniles (IJs) or infected insect cadavers. Spent medium from culturing the bacterial symbionts Xenorhabdus bovienii and Photorhabdus luminescens kayaii with the cells removed was also applied without their nematode partners. RESULTS The aqueous suspensions of IJs, infected cadaver applications of EPNs and especially treatments of X. bovienii supernatant suppressed the negative impact of RKNs on tomatoes. Specific responses to treatment were reduced RKN egg masses, increased plant height and increased fresh and dry weights compared with the control where only RKNs were applied. CONCLUSION Among the treatments tested, the plant-dipping method of X. bovienii into bacterial culture fluid may be the most practical and effective method for M. incognita and M. arenaria control. © 2015 Society of Chemical Industry

Early development of the root-knot nematode Meloidogyne incognita

Abstract: Detailed descriptions of the early development of parasitic nematodes are seldom available. The embryonic development of the plant-parasitic nematode Meloidogyne incognita was studied, focusing on the early events. A fixed pattern of repeated cell cleavages was observed, resulting in the appearance of the six founder cells 3 days after the first cell division. Gastrulation, characterized by the translocation of cells from the ventral side to the center of the embryo, was seen 1 day later. Approximately 10 days after the first cell division a rapidly elongating two-fold stage was reached. The fully developed second stage juvenile hatched approximately 21 days after the first cell division. When compared to the development of the free-living nematode Caenorhabditis elegans, the development of M. incognita occurs approximately 35 times more slowly. Furthermore, M. incognita differs from C. elegans in the order of cell divisions, and the early cleavage patterns of the germ line cells. However, cytoplasmic ruffling and nuclear migration prior to the first cell division as well as the localization of microtubules are similar between C. elegans and M. incognita.

Resistance to Southern Root-knot Nematode (Meloidogyne incognita) in Wild Watermelon (Citrullus lanatus var. citroides).

Abstract: Southern root-knot nematode (RKN, Meloidogyne incognita) is a serious pest of cultivated watermelon (Citrullus lanatus var. lanatus) in southern regions of the United States and no resistance is known to exist in commercial watermelon cultivars. Wild watermelon relatives (Citrullus lanatus var. citroides) have been shown in greenhouse studies to possess varying degrees of resistance to RKN species. Experiments were conducted over 2 yr to assess resistance of southern RKN in C. lanatus var. citroides accessions from the U.S. Watermelon Plant Introduction Collection in an artificially infested field site at the U.S. Vegetable Laboratory in Charleston, SC. In the first study (2006), 19 accessions of C. lanatus var. citroides were compared with reference entries of Citrullus colocynthis and C. lanatus var. lanatus. Of the wild watermelon accessions, two entries exhibited significantly less galling than all other entries. Five of the best performing C. lanatus var. citroides accessions were evaluated with and without nematicide at the same field site in 2007. Citrullus lanatus var. citroides accessions performed better than C. lanatus var. lanatus and C. colocynthis. Overall, most entries of C. lanatus var. citroides performed similarly with and without nematicide treatment in regard to root galling, visible egg masses, vine vigor, and root mass. In both years of field evaluations, most C. lanatus var. citroides accessions showed lesser degrees of nematode reproduction and higher vigor and root mass than C. colocynthis and C. lanatus var. lanatus. The results of these two field evaluations suggest that wild watermelon populations may be useful sources of resistance to southern RKN.

Biofumigant effect of new defatted seed meals against the southern root-knot nematode, Meloidogyne incognita

Abstract: In recent years, Brassica carinata defatted seed meals (DSMs) have been successfully applied as an amendment in the control of pests and soil pathogens in several countries with clear advantages for the environment and soil fertility. The effectiveness of this product is clearly linked to the release of bioactive compounds by the well-known glucosinolate (GL)–myrosinase (MYR) system. Until now, this commercial know-how has been limited to allyl-isothiocyanate, the breakdown product of hydrolysis catalysed by MYR of the GL sinigrin. Brassicaceae germplasm is an extremely wide-ranging family, considering that more than 3500 species have been classified in this family in nature, which contains around 200 different GLs. Therefore, there is a great potential for the availability of new still unexplored bioactive compounds. This study evaluated, in controlled glasshouse conditions, the effect of biofumigation on the nematode Meloidogyne incognita and that of biostimulation on tomato plants of 13 DSMs obtained from different Brassicaceae species at different levels of soil inoculation. Among the tested DSMs, the best results for all inoculations were achieved by Eruca sativa (rocket), Barbarea verna (land cress) and Brassica nigra (black mustard), whereas the other species gave either alternate results or results not different from untreated or sunflower DSM controls. All the DSMs, including sunflower, determined a clear positive effect on plant vigour. These first results open new perspectives for the application of biofumigation in plant protection and management.

Systemic acquired resistance activation in solanaceous crops as a management strategy against root‐knot nematodes

Abstract: BACKGROUND Activators of systemic acquired resistance (SAR), such as salicylic acid (SA) and its synthetic functional analogues benzo(1,2,3)thiadiazole-7-carbothionic acid-S-methyl ester (BTH) and 2,6-dichloroisonicotinic acid (INA), were tested on tomato, eggplant and pepper for the control of the root-knot nematode Meloidogyne incognita. Effects on plant fitness, nematode reproduction and root galling were screened in relation to different methods of application, to different applied dosages of chemicals and to different plant growth stages. Dosages applied to plants were in relation to plant weights. These chemicals were also tested for their possible nematotoxic activity in vitro. RESULTS Soil drenches of SA and INA and root dip application of SA and BTH inhibited nematode reproduction, at specific dosage ranges, without affecting plant growth. SA and INA were able to reduce root galling as well. Foliar sprays of both SA and BTH were ineffective against nematode attacks. Plants tolerated SA more than the other chemicals tested. BTH at elevated concentrations increased the mortality of nematode juveniles and reduced egg hatching in vitro. CONCLUSIONS SAR activators at concentrations suitable for different plant growth stages and applied by the proper method can possibly be included in IPM programmes for nematode management. © 2015 Society of Chemical Industry