Water Stress Differentially Modulates the Expression of Tomato Cell Wall Metabolism-Related Genes in Meloidogyne incognita Feeding Sites.

Microscopic observations and transcriptomic RNA-Seq analyses were applied to investigate the effect of water stress during the formation of tomato galls formation 1 and 2 weeks after inoculation with the root-knot nematode Meloidogyne incognita. Water stress affected root growth and the nematode ability to mount an efficient parasitism. The effects of water stress on the feeding site development were already observed at 1 week after nematode inoculation, with smaller giant cells, delayed development, and thinner cell walls. These features suggested changes in the expression levels of genes involved in the feeding site formation and maintenance. Gene Ontology (GO) enrichment and expression patterns were used to characterize differentially expressed genes. Water stress modified the expression profile of genes involved in the synthesis, degradation, and remodeling of the cell wall during the development of nematode feeding site. A comparison of gene expression with unstressed galls revealed that water stress intensified the up or downregulation of most genes. However, it particularly influenced the expression pattern of expansin A11 (Solyc04g081870.4.1), expansin-like B1(Solyc08g077910.3.1), a pectin acetylesterase (Solyc08g005800.4.1), and the pectin methylesterase pmeu1 (Solyc03g123630.4.1) which were upregulated in unstressed galls and repressed by water stress, at both sampling times. The expression of most members of the genes involved in cell wall metabolism, i.e., those coding for Csl, fasciclin, and COBRA proteins, were negatively influenced. Interestingly, alteration in the expression profiles of most dirigent protein genes (DIRs) and upregulation of five gene coding for Casparian strip domain protein (CASP)-like proteins were found. Gene expression analysis of galls from water stressed plants allowed us to better understand the molecular basis of M. incognita parasitism in tomato. Specific genes, including those involved in regulation of cellulose synthesis and lignification process, require further study to develop defense strategies against root-knot nematodes.

Marine Organisms for the Sustainable Management of Plant Parasitic Nematodes.

Plant parasitic nematodes are annually responsible for the loss of 10%-25% of worldwide crop production, most of which is attributable to root-knot nematodes (RKNs) that infest a wide range of agricultural crops throughout the world. Current nematode control tools are not enough to ensure the effective management of these parasites, mainly due to the severe restrictions imposed on the use of chemical pesticides. Therefore, it is important to discover new potential nematicidal sources that are suitable for the development of additional safe and effective control strategies. In the last few decades, there has been an explosion of information about the use of seaweeds as plant growth stimulants and potential nematicides. Novel bioactive compounds have been isolated from marine cyanobacteria and sponges in an effort to find their application outside marine ecosystems and in the discovery of new drugs. Their potential as antihelmintics could also be exploited to find applicability against plant parasitic nematodes. The present review focuses on the activity of marine organisms on RKNs and their potential application as safe nematicidal agents.

Abamectin Efficacy on the Potato Cyst Nematode Globodera pallida.

The potato cyst nematode Globodera pallida is a major pest of the potato crop. Abamectin is a biological pesticide showing high nematicide activity, but its efficacy to control G. pallida has not been investigated to date. In this study, combination of different abamectin concentrations ranging from 1.125 to 36 µg/mL x exposure times from 24 to 384 h were tested on the nematode in a hatching test. Abamectin induced mortality with LD50 value in the range of 13.23 (after 24 h) to 2.90 µg/mL (after 384 h). A glasshouse experiment was also performed in pots filled with soil infected with G. pallida in the presence of sprouted potato tubers cultivar "Spunta". Abamectin at 4.5, 9.0, 18.0 and 36.0 µg/mL was used in comparison with nematicide fosthiazate. The doses of 18 and 36 µg/mL significantly reduced number of eggs, juveniles, cyst/g soil and reproduction rate in comparison to both untreated control and fosthiazate treatment. Soil applications of abamectin provided significant G. pallida control with LD50 and LD99.9 of 14.4 and 131.3 µg/mL, respectively. These results indicate the efficacy of abamectin to control G. pallida on potato crops and its potential use in organic agriculture or in an integrated pest management program.

Transcriptomic Responses to Water Deficit and Nematode Infection in Mycorrhizal Tomato Roots.

Climate changes include the intensification of drought in many parts of the world, increasing its frequency, severity and duration. However, under natural conditions, environmental stresses do not occur alone, and, in addition, more stressed plants may become more susceptible to attacks by pests and pathogens. Studies on the impact of the arbuscular mycorrhizal (AM) symbiosis on tomato response to water deficit showed that several drought-responsive genes are differentially regulated in AM-colonized tomato plants (roots and leaves) during water deficit. To date, global changes in mycorrhizal tomato root transcripts under water stress conditions have not been yet investigated. Here, changes in root transcriptome in the presence of an AM fungus, with or without water stress (WS) application, have been evaluated in a commercial tomato cultivar already investigated for the water stress response during AM symbiosis. Since root-knot nematodes (RKNs, Meloidogyne incognita) are obligate endoparasites and cause severe yield losses in tomato, the impact of the AM fungal colonization on RKN infection at 7 days post-inoculation was also evaluated. Results offer new information about the response to AM symbiosis, highlighting a functional redundancy for several tomato gene families, as well as on the tomato and fungal genes involved in WS response during symbiosis, underlying the role of the AM fungus. Changes in the expression of tomato genes related to nematode infection during AM symbiosis highlight a role of AM colonization in triggering defense responses against RKN in tomato. Overall, new datasets on the tomato response to an abiotic and biotic stress during AM symbiosis have been obtained, providing useful data for further researches.

Ozone treatments activate defence responses against Meloidogyne incognita and Tomato spotted wilt virus in tomato.

BACKGROUND: Ozonated water (O3 wat) soil drench and/or foliar spray applications were evaluated for their potential to control the root-knot nematode Meloidogyne incognita (RKN) and the airborne pathogen Tomato spotted wilt virus (TSWV) in tomato. We investigated how O3 wat modulates the salicylic acid/jasmonic acid/ethylene (SA/JA/ET) signalling network in the host, locally and systemically, to induce resistance to nematode and virus. RESULTS: The application as soil drench was effective in reducing the number of galls and egg masses, but did not reduce the incidence and severity of TSWV infection. Conversely, O3 wat applied by foliar spray decreased TSWV disease incidence and severity (-20%), but was not able to control M. incognita infection. SA-related genes were generally upregulated in both locally treated and systemically reached tissues, showing a positive action of the O3 wat treatment on SA signalling. Neither O3 wat application method significantly altered JA-related gene expression in either direction. ET-related genes were differentially regulated by root or leaf treatments, indicating that O3 wat may have different effects on ET-mediated signalling in different organs. JA/ET/SA related pathways were differentially modulated by O3 wat in the presence of either RKN or TSWV. CONCLUSION: O3 wat had a higher efficacy when applied directly to organs challenged by the pathogens, although it was potentially able to stimulate defence responses through the activation of SA signalling. Owing to its safety and effectiveness in controlling nematode and virus infections, O3 wat can be considered as a possible alternative tool for sustainable disease management practices. © 2019 Society of Chemical Industry.

Interaction between the photosynthetic anoxygenic microorganism Rhodobacter sphaeroides and soluble gold compounds. From toxicity to gold nanoparticle synthesis.

Biological processes using microorganisms for nanoparticle synthesis are appealing as eco-friendly nanofactories. The response of the photosynthetic bacterium Rhodobacter sphaeroides to gold exposure and its reducing capability of Au(III) to produce stable gold nanoparticles (AuNPs), using metabolically active bacteria and quiescent biomass, is reported in this study. In the former case, bacterial cells were grown in presence of gold chloride at physiological pH. Gold exposure was found to cause a significant increase of the lag-phase duration at concentrations higher than 10 µM, suggesting the involvement of a resistance mechanism activated by Au(III). Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry (SEM/EDS) analysis of bacterial cells confirmed the extracellular formation of AuNPs. Further studies were carried out on metabolically quiescent biomass incubated with gold chloride solution. The biosynthesized AuNPs were spherical in shape with an average size of 10 ±â€¯3 nm, as analysed by Transmission Electron Microscopy (TEM). The nanoparticles were hydrophilic and stable against aggregation for several months. In order to identify the functional groups responsible for the reduction and stabilization of nanoparticles, AuNPs were analysed by Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), X-ray Fluorescence Spectrometry (XRF) and X-ray Absorption Spectroscopy (XAS) measurements. The obtained results indicate that gold ions bind to functional groups of cell membrane and are subsequently reduced by reducing sugars to gold nanoparticles and capped by a protein/peptide coat. Gold nanoparticles demonstrated to be efficient homogeneous catalysts in the degradation of nitroaromatic compounds.

Changes in lignin biosynthesis and monomer composition in response to benzothiadiazole and root-knot nematode Meloidogyne incognita infection in tomato.

Benzothiadiazole (BTH) acts as a priming agent in plant defence leading to a reduction in penetration and development of the root-knot nematode Meloidogyne incognita in susceptible tomato roots. Changes in lignin biosynthesis in the susceptible tomato cv. Roma following nematode infection and/or BTH treatment were investigated in comparison to the resistant cv. Rossol. Both untreated and BTH-treated susceptible infected roots (galls) showed an increased level of expression of lignin synthesis-related genes (PAL, C4H, HCT and F5H) at early times during infection (2-4 days post inoculation). Peroxidase (soluble and cell-wall bound, POX) enzyme activities increased after inoculation with M. incognita and the priming effect of BTH treatment was evident at later stages of infection (7 days post inoculation). As expected, the induction of PAL and POXs and lignin synthesis-related genes was faster and greater in resistant roots after infection. Histochemical analysis revealed accumulation of higher lignin levels at later infection stages in BTH-treated galls compared to untreated ones. Furthermore, the monomer composition of lignin indicated a different composition in guaiacyl (G) and syringyl (S) units in BTH-treated galls compared to untreated galls. The increase in G units made G/S ratio similar to that in the resistant genotype. Overall, lignin played a critical role in tomato defence to M. incognita in response to BTH.

Ozonated water reduces susceptibility in tomato plants to Meloidogyne incognita by the modulation of the antioxidant system.

Few studies have been carried out on the effect of ozonated water (O3 wat) on the oxidative stress of root systems and, in particular, in combination with biotic stress. The aim of this study was to determine whether aqueous ozone is effective in the control of root-knot nematode (RKN) infection and to investigate the concomitant changes in the basal defence system. A tomato cultivar susceptible to Meloidogyne incognita was treated with O3 wat as a soil drench. No negative effects were seen following ozone application in comparison with the control under the exposure conditions used. The treatment reduced significantly the nematode infection rate and induced changes in the morphology of nematode feeding sites, some of which were characterized by visible symptoms of senescence. The antioxidant response, as well as parameters of oxidative damage, were examined in untreated and O3 wat-treated galls at 2, 4 and 7 days after inoculation and compared with uninfected roots. High levels of reactive oxygen species (ROS), H2 O2 and malondialdehyde were generated in galls in response to combined abiotic and biotic stresses. Throughout the experimental period, the activities and relative transcript levels of the antioxidant enzymes catalase, superoxide dismutase and ascorbate peroxidase produced different responses when exposed to ozone treatment and/or infection. The results demonstrate how O3 wat protects tomato against the RKN M. incognita through the modulation of basal defence mechanisms.

Benzothiadiazole effect in the compatible tomato-Meloidogyne incognita interaction: changes in giant cell development and priming of two root anionic peroxidases.

MAIN CONCLUSION: BTH application is effective in root-knot nematode-tomato interaction in a way that involves a delay in the formation of nematode feeding site and triggers molecular responses at several levels. The compatible interaction between root-knot nematodes and their hosts requires the nematode to overcome plant defense systems so that a sophisticated permanent feeding site (giant cells) can be produced within the host roots. It has been suggested that activators of plant defenses may provide a novel management strategy for controlling root-knot nematodes but little is known about the molecular basis by which these elicitors operate. The role of pre-treatment with Benzothiadiazole (BTH), a salicylic acid analog, in inducing resistance against Meloidogyne incognita infection was investigated in tomato roots. A decrease in galling in roots and feeding site numbers was observed following BTH treatment. Histological investigations showed a delay in formation of feeding sites in treated plants. BTH-treated galls had higher H2O2 production, lignin accumulation, and increased peroxidase activity than untreated galls. The expression of two tomato genes, Tap1 and Tap2, coding for anionic peroxidases, was examined by qRT-PCR and in situ hybridization in response to BTH. Tap1 was induced at all infection points, reaching the highest level at 15 dpi. Tap2 expression, although slightly delayed in untreated galls, increased during infection in both treated and untreated galls. The expression of Tap1 and Tap2 was observed in giant cells of untreated roots, whereas the transcripts were localized in both giant cells and in parenchyma cells surrounding the developing feeding sites in treated plants. These results show that BTH applied to tomato plants makes them more resistant to infection by nematodes, which become less effective in overcoming root defense pathway.