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Root-knot nematodes ( Meloidogyne spp.) have been reported to be responsible for large economic losses of agricultural crops due to their wide host range and variety of suitable climates. The control measures of these parasitic nematodes depend upon synthetic nematicides and a small number bio-based products. Chemical nematicides are eliciting adverse effects on the environment and human health. In the present study, an alternative tool, nano-chitosan was tested for the control the root-knot nematodes, Meloidogyne incognita , and Tobacco mosaic tobamovirus (TMV) in greenhouse-cultivated tomato. The effect of nano-chitosan on morphological (weight and length of shoot and root systems) and biochemical responses (Polyphenol oxidase, Peroxides, Total soluble phenol and Total protein) was assessed. The obtained results indicated that densities of Meloidogyne incognita alone or in the presence of TMV were decreased by nano-chitosan at a range of 45.89 to 66.61%, while root gall desntiy was reduced between 10.63 and 67.87%. Moreover, the density of TMV on tomato leaves singly or in the presence of M. incognita was suppressed at range of 10.26 to 65.00% after 20 days of infection, and reached up to 58.00% after 40 days of infection. However, soil application of nano-chitosan pre infection reduced TMV density only by 5.48%. Morphogenesis of tomato plants such as shoot and root systems were significantly improved. The impacts of nano-Chitosan applications on total soluble phenol, total protein, polyphenol oxidase and peroxides after 20 and 40 days of infections varied.

Root-knot nematodes are obligate endoparasites that maintain a biotrophic relationship with their hosts over a period of several weeks. They induce the differentiation of root cells into specialized multinucleate hypertrophied feeding cells known as giant cells. Nematode effectors synthesized in the esophageal glands and injected into the plant tissue through the syringe-like stylet play a key role in giant cell ontogenesis. The Meloidogyne incognita MiEFF1 is one of the rare effectors of phytopathogenic nematodes to have been located in vivo in feeding cells. This effector specifically targets the giant cell nuclei. We investigated the Arabidopsis functions modulated by this effector, by using a yeast two-hybrid approach to identify its host targets. We characterized a universal stress protein (USP) and cytosolic glyceraldehyde-3-phosphate dehydrogenases (GAPCs) as the targets of MiEFF1. We validated the interaction of MiEFF1 with these host targets in the plant cell nucleus, by bimolecular fluorescence complementation (BiFC). A functional analysis with Arabidopsis GUS reporter lines and knockout mutant lines showed that GAPCs were induced in giant cells and that their non-metabolic functions were required for root-knot nematode infection. These susceptibility factors are potentially interesting targets for the development of new root-knot nematode control strategies.

The Cowpea (Vigna unguiculata L. Walp), is arguably commonly cultivated legume crop within sub-Saharan African region. However, regardless of the continuous increase in cultivated area for cowpea, production is significantly low. One of the most apparent biotic hindrances to cowpea yield is Meloidogyne incognita’s infection. Application of synthetic nematicides is an efficient way of managing M. incognita on cowpea. However, the consideration for human and environmental safety has prompted research into innumerable substitutes inclusive of plant-mediated nanoparticles. In this study, probable nematicidal action of Borreria verticillata (L.) G. Mey. mediated nanoparticles obtained from copper, iron and zinc was assessed on M. incognita. The likely impact of each nanoparticle (NP) on quality of harvested cowpea seeds was equally evaluated. Copper, zinc and iron nanoparticles showed maximum absorbance at 308, 318 and 304 nm, respectively. Fourier-transform infrared (FTIR) spectra demonstrated notable bands attesting to B. verticillata secondary metabolites as reducing agents in the formation of NPs (4.85–50 nm). CuNPs at 100 ppm significantly increased cowpea yield by 339.8% with reference to untreated cowpea plants, while reduction in number of nematode egg mass, juvenile population in cowpea roots per 200 cc of soil was achieved with Cu and Zn NPs relative to the standard carbofuran. Oil absorption capacity was higher in Cu and Zn NPs treated seeds, bulk density was uniformly high in Cu, Zn and Fe NPs compared with untreated control seeds. No significant difference in physical characteristics of NP treated cowpea seeds. This study corroborates previous reports regarding the efficacy of some green plants serving as reducing agents in the biosynthesis of metal NPs. B. verticillata has proved potent in this regard particularly in our current study. The NPs obtained displayed qualities of a suitable substitute for synthetic nematicides in the prospect of M. incognita management, without any inconsistency in cowpea food functionality.

Recently, studies on climate change have highlighted the central role of photosynthetic mechanisms in the defense response of plants to abiotic and biotic stresses. Photo-sensing and photo-activation are innovative technologies applied for the early detection of plant pathogens in order to prevent the dramatic impact they may have on plants. Chlorophyll Fluorescence Imaging (CFI) and Laser-Induced Breakdown Spectroscopy (LIBS) analytical techniques can be used to evaluate the amount of chlorophyll in plants, which can be altered in the case of biotic and abiotic stresses. In this work, both techniques were applied to two pathogenic model systems, i.e., roots of susceptible tomato plants infected by Meloidogyne incognita and Nicotiana benthamiana plants infected by cymbidium ringspot virus. Experimental evidence is provided and discussed showing that specific application protocols of both methods can be used successfully for the early detection of symptoms of the pathogen attacks of Meloidogyne incognita on tomato roots and of cymbidium ringspot virus infected plants. In particular, a decrease in chlorophyll content was measured by fluorescence imaging, and an increase in Mg++ content was determined by LIBS in both the leaves and stems of infected tomato plants and the leaves of infected plants, with respect to control (non-infected) plants. Thus, the two techniques used have been shown to be able to discriminate satisfactorily between control and infected plants and to provide some insight on the underlying mechanisms of plant defenses again nematodes and viruses.

Plants mediate interactions between different herbivores that attack simultaneously or sequentially aboveground (AG) and belowground (BG) organs. The local and systemic activation of hormonal signaling pathways and the concomitant accumulation of defense metabolites underlie such AG-BG interactions. The main plant-mediated mechanisms regulating these reciprocal interactions via local and systemic induced responses remain poorly understood. We investigated the impact of root infection by the root-knot nematode (RKN) Meloidogyne incognita at different stages of its infection cycle, on tomato leaf defense responses triggered by the potato aphid Macrosiphum euphorbiae . In addition, we analyzed the reverse impact of aphid leaf feeding on the root responses triggered by the RKN. We focused specifically on the signaling pathways regulated by the phytohormones jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA), and indole-3-acetic acid (IAA) as well as steroidal glycoalkaloids as induced defense compounds. We found that aphid feeding did not induce AG hormonal signaling, but it repressed steroidal glycoalkaloids related responses in leaves, specifically when feeding on plants in the vegetative stage. Root infection by the RKN impeded the aphid-triggered repression of the steroidal glycoalkaloids-related response AG. In roots, the RKN triggered the SA pathway during the entire infection cycle and the ABA pathway specifically during its reproduction stage. RKN infection also elicited the steroidal glycoalkaloids related gene expression, specifically when it was in the galling stage. Aphid feeding did not systemically alter the RKN-induced defense responses in roots. Our results point to an asymmetrical interaction between M. incognita and Ma. euphorbiae when co-occurring in tomato plants. Moreover, the RKN seems to determine the root defense response regardless of a later occurring attack by the potato aphid AG.

Nematodes are widespread organisms and pose a serious problem in vegetable production. The use of synthetic nematicides is a common method of bringing down the nematode population to increase crop yield. This has, however, brought about serious pollution to the environment. Leaves and twigs of were extracted in organic solvents and then chromatographed on a silica gel column. Chromatographic fractions obtained from the methanol and acetone crude extracts were characterized with UV-visible, FTIR, and GCMS and tested for their potential nematode suppressing activity in field micro plots. Spectroscopic analysis of the fractions revealed the presence of compounds such as aldehydes, acids, ketones, phenols, terpenes, hydrocarbons, and fatty acid esters. The extract fractions of were applied at 100, 75, and 50 mg·ml at 100 ml each and carbofuran at 0.5, 1.0, and 1.5 kg a.i.·ha . The vegetative growth of pepper plants as well as the number and weight of fruits increased significantly in plants treated with the above-mentioned extract fractions. The protective role of fractions compared favorably with the synthetic nematicide (carbofuran). The most effective in reduction of the nematode population, and plant growth and yield was the highest concentration of 100 mg·ml . Thus, organic solvent extract fractions from can serve as a biopesticide and an alternative to the environmentally hazardous synthetic nematicide.

Rhizosphere microorganisms and the volatile organic compounds (VOCs) produced by them take part in the regulation of the chemotaxis of nematodes. A total of 150 strains of rhizosphere bacteria were screened via a chemotaxis experiment with Meloidogyne incognita. Some isolates affected the behavior of the nematodes, including attraction, randomness, and repulsion. Volatile metabolites produced via the selected bacteria were associated with the chemotaxis of nematodes. M. incognita was highly attracted to decanal. In addition, dimethyl disulfide, 2,5-dimethylpyrazine, pentadecanoic acid, and palmitic acid were found to attract weakly M. incognita. Furthermore, the chemotaxis of M. incognita was tested in a pot experiment. The bacteria Bacillus sp. 1-50, Brevibacillus brevis 2-35, B. cereus 5-14, Chryseobacterium indologens 6-4, and VOC decanal could regulate the movement of M. incognita in the pot with or without plants. The results provide insights into rhizosphere microorganisms and their VOCs and how they regulate the chemotaxis of the nematodes.

Forty-four bacterial strains isolated from greenhouse soil and beetroots were tested for their antagonistic activity against the plant-parasitic root-knot nematode (RKN) Meloidogyne incognita, which causes significant yield losses in a number of important crops worldwide. Through a novel combination of in vitro and on planta screening assays, Pseudomonas spp. 105 and 108 were identified as the most promising bacterial isolates. Both strains were evaluated for their potential to control different RKN population densities and as root protectants against nematode infestation. Regardless of the application method, both strains significantly reduced root galling caused by M. incognita. These two strains were subjected to whole genome sequencing and de novo genome assembly as a basis for phylogenetic and future functional characterization. Phylogenetic analysis revealed that both Pseudomonas strains cluster within the Pseudomonas fluorescens clade among previously characterized RKN antagonists and Pseudomonas-based biocontrol agents of plant diseases.

Plant-parasitic nematodes secrete numerous effectors to facilitate parasitism, but detailed functions of nematode effectors and their plant targets remain largely unknown. Here, we characterized four macrophage migration inhibitory factors (MIFs) in Meloidogyne incognita resembling the MIFs secreted by human and animal parasites. Transcriptional data showed MiMIFs are up-regulated in parasitism. Immunolocalization provided evidence that MiMIF proteins are secreted from the nematode hypodermis to the parasite surface, detected in plant tissues and giant cells. In planta MiMIFs RNA interference in Arabidopsis decreased infection and nematode reproduction. Transient expression of MiMIF-2 could suppress Bax- and RBP1/Gpa2-induced cell death. MiMIF-2 ectopic expression led to higher levels of Arabidopsis susceptibility, suppressed immune responses triggered by flg22, and impaired [Ca2+](cyt) influx induced by H2O2. The immunoprecipitation of MiMIF-2-interacting proteins, followed by co-immunoprecipitation and bimolecular fluorescence complementation validations, revealed specific interactions between MiMIF-2 and two Arabidopsis annexins, AnnAt1 and AnnAt4, involved in the transport of calcium ions, stress responses, and signal transduction. Suppression of expression or overexpression of these annexins modified nematode infection. Our results provide functional evidence that nematode effectors secreted from hypodermis to the parasite cuticle surface target host proteins and M. incognita uses MiMIFs to promote parasitism by interfering with the annexin-mediated plant immune responses.

Root-knot nematode (Meloidogyne incognita) is a serious pest of vegetables and major limiting factor in the commercial production of carrot in many parts of the world, including India. To avoid excess use of chemicals, an attempt was made to manage M. incognita infecting carrot by using bioagents viz., Trichoderma harzianum (indigenous and commercial) and Pseudomonas fluorescens (commercial) under field conditions. Among biocontrol agents, the lowest nematode population in soil (222.66/200 g) was recorded in isolated T. harzianum @ 25g/m^sup 2^ (2 × 10^sup 6^ Cfu/g) treated plot than by commercial T. harzianum @ 20g/m^sup 2^. Maximum reduction of galls/rhizome (11.00), galls/5 g of root (36.00) and egg masses (11.33) per 5 gram of root was recorded in isolated T. harzianum @ 25g/m^sup 2^ treatment compared to other treatments. Maximum shoot height (49.66 cm), shoot weight (26.00 g/rhizome) and rhizome yield (8.20 q/ha) were also recorded in isolated T. harzianum @ 25g/m^sup 2^ followed by isolated T. harzianum and commercial T. harzianum @ 20g/m^sup 2^.