Meloidogyne Incognita Populations Research Articles

Effect of Temperature on the Embryogenesis of Three Geographically Distinct Populations of Meloidogyne incognita Is Driven by Intrinsic Thermal Acclimation Reaction.

Research interest in the mechanisms enabling plant-parasitic nematodes to adjust their physiological performance and cope with changing temperatures has intensified in light of global warming. Here, we show that geographically distinct populations of the root-knot nematode Meloidogyne incognita, which is prevalent in the three main pepper-growing regions in Israel-Carmel Valley (Carmel), Jordan Valley (JV), and Arava Rift (Arava)-possess persistent differences in their thermal acclimation capacity, which affect pre- and postembryonic development. The optimal temperature for embryonic growth completion was 25°C for the Carmel population; 25 and 30°C for the JV population; and 30°C for the Arava population. Cumulative hatching percentages showed variations among populations; relative to hatching at 25°C, the Carmel population experienced hatching reduction at the higher studied temperatures 30 and 33°C, while the JV and Arava populations exhibited an increase in hatching at 30 and 33°C, respectively. Juvenile survival indicates that at the lowest temperature (20°C), the Carmel population gained the highest survival rates throughout the experimental duration, while at the same duration at 33°C, the Arava population gained the highest survival rate. Infective juveniles of the Carmel population demonstrated increased penetration of tomato roots at 25°C compared to the JV and Arava populations. Inversely, at 33°C, increased penetration was observed for the Arava compared to the Carmel and JV populations. Altogether, the Arava population's performance at 33°C might incur distinct fitness costs, resulting in consistent attenuation compared to the Carmel population at 25°C. Precisely defining a population's thermal acclimation response might provide essential information for models that predict the impact of future climate change on these populations.

Identification and Characterization of a Virulent Meloidogyne incognita Population Breaking Tomato Mi-1-Mediated Resistance in Indiana

High-tunnel production is increasing rapidly in the US due to its effectiveness in extending production seasons. Tomato is considered one of the most profitable crops grown in high tunnels. The elevated soil temperature and constant soil moisture in high tunnels lead to the buildup of root-knot nematodes (RKNs). Growing RKN-resistant tomato cultivars or grafting onto RKN-resistant tomato rootstocks is considered effective in managing RKNs. However, all of the RKN-resistant tomato cultivars or rootstocks carry the same resistance gene, Mi-1. This lack of diversity in resistance has led to the emergence of virulent RKN populations breaking tomato Mi-1 resistance. Here, we identified and characterized a virulent population of Meloidogyne incognita from a high tunnel in Indiana. The M. incognita population was confirmed as being able to infect and reproduce on two resistant tomato cultivars, Better Boy and Early Girl, carrying the Mi-1 gene, under a controlled environment at 24 °C. To our knowledge, this is the first report of a virulent M. incognita population breaking Mi-1 resistance in Indiana. Virulent M. incognita populations overcoming Mi-1 resistance were previously reported in California and Georgia in the US. This work emphasizes the importance of regularly monitoring RKN population virulence to sustainably manage the pest.

Biological nematicides as an alternative for control of Meloidogyne incognita populations in yellow pitahaya (Sselenicereus megalanthus).

Yellow pitahaya in the Ecuadorian Amazon has become one of the most important economic crops in the region. However, the presence of pests (nematodes) in the soil has caused up to 100% of the crop's growth stages to be affected. Faced with this problem, growers use various chemical nematicides that minimize this impact but cause contamination problems. For this reason, the objective of the research was to evaluate microorganisms that control or reduce the population of Meloidogyne incognita in the pitahaya crop at the greenhouse level. The design was DBCA, and the statistical analysis was performed with the statistical package Infostat 2017, using linear mixed models and Fisher's tests at 5%. The results show that root nodules decrease when P. lilacinum + T. asperellum is applied after nematode injection (261). In addition, the lowest number of nodulations (251) was obtained when microorganisms were applied after nematode inoculation (251 nodulations). Still, when microorganisms were used before, aerial biomass growth was stimulated (384.17 g) even when nematodes were present in the root system. Keywords: microorganisms; nematodes; pitahaya.

Morphologic, Morphometric, and Molecular Characterization of Vietnamese Populations of Meloidogyne incognita.

Meloidogyne incognita is considered the most damaging and common root-knot nematode to numerous host plants worldwide. During a survey of nematodes in Vietnam, 1,106 samples from 22 different plant species were collected. M. incognita was recorded on 13 of the 22 host plants. Four populations of M. incognita from four host plants were chosen for comparison and confirmation of their morphologic, morphometric, and molecular characteristics. Genetically based phylogenetic trees were constructed to show relationships among root-knot nematodes. Molecular barcodes of four gene regions, ITS, D2-D3 of 28S rRNA, COI, and Nad5 mtDNA, integrated with morphologic and morphometric data were used as reliable references for molecular identification of M. incognita. Our analyses indicated that tropical root-knot nematodes are very similar in characterization of ITS, D2-D3 of 28S rRNA, and COI regions. However, these gene regions can be used to separate the tropical root-knot nematode group from other groups. On the other hand, the analysis of Nad5 mtDNA and multiplex-PCR with specific primers can be used to distinguish tropical species.

Solarized IPM Module for Biocontrol of Root-knot Nematode on Tomato at Nursery Level in District G.B Nagar, Uttar Pradesh

Background: The role of soil solarization in suppression of soil borne pathogens and weeds has been established by several researchers around the globe It involves capturing solar radiations when the soil receives the maximum sunlight in May-June using a polythene mulch. Its effectiveness depends on ambient temperature, duration of the treatments and soil moisture. This not only acts as a soil disinfectant but also as soil decontamination. It includes various changes in the soil like physical, chemical and biological properties. Methods: The field to lab and vice-versal based investigations were carried during 2021-2022 at Amity Centre for Biocontrol and Plant Disease Management, Amity University, Uttar Pradesh, Noida and identified tomato nurseries of district G B Nagar where heavy infestation (10-12 J2/cc soil) of root knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood was recorded. The treatments comprised of sustainable components viz. deoiled seed cake of neem, a Arbuscular Mycorrhizal fungus Glomus intraradices and indigenous fungal strain of Trichoderma harzianum, (Th7) alone and together applied for evolving IPM module at solarized and unsolarized sets. Under microplot trials, the entire solarized treatments were carried out measuring 3 × 1 sq. meter each in which one set of all the treatments including control covered with clear transparent polythene sheet (400 ì gauge) for solarization. The treatments were replicated thrice in randomized block design. Result: The observations of solarized and unsolarized treatments clearly revealed that the soil solarization in treatments where the sun radiant energy was trapped by 400 µ transparent polysheets significantly reduced the root knot nematode Meloidogyne incognita population both in root and soil in comparison to unsolarized treatments where no solar energy trapping was done. The combined application of locally isolated Trichoderma harzianum (Th7) and VA mycorrhiza, Glomus intraredices enhanced germination and plant growth in nurseries. In the present investigation, the solarized IPM module- 4 comprising of other sustainable components viz. neem oil-seed cake, T. harzianum (Th-7) and Arbuscular Mycorrhizal (AM) fungus G. intraredices is proved to be an ideal one in root-knot nematode pest management in tomato nurseries.

Crop rotation with Meloidogyne-resistant germplasm is useful to manage and revert the (a)virulent populations of Mi1.2 gene and reduce yield losses.

A rotation sequence of ungrafted and grafted tomato-melon-pepper-watermelon on resistant rootstocks 'Brigeor', Cucumis metuliferus, 'Oscos' and Citrullus amarus, respectively, was carried out in a plastic greenhouse, ending with a susceptible or resistant tomato crop. The rotation was conducted in plots infested by an avirulent (Avi) or a partially virulent (Vi) Meloidogyne incognita population to the Mi1.2 gene. At the beginning of the study, the reproduction index (RI, relative reproduction in the resistant respect susceptible tomato) of Avi and Vi populations was 1.3% and 21.6%, respectively. Soil nematode density at transplanting (Pi) and at the end (Pf) of each crop, disease severity and crop yield were determined. Moreover, the putative virulence selection and fitness cost were determined at the end of each crop in pot tests. In addition, a histopathological study was carried out 15 days after nematode inoculation in pot test. The volume and number of nuclei per giant cell (GC) and the number of GC, their volume and the number of nuclei per feeding site in susceptible watermelon and pepper were compared with C. amarus and resistant pepper. At the beginning of the study, the Pi of Avi and Vi plots did not differ between susceptible and resistant germplasm. At the end of the rotation, the Pf of Avi was 1.2 the Pi in susceptible and 0.06 in resistant, the cumulative yield of grafted crops was 1.82 times higher than that of the ungrafted susceptible ones, and the RI in resistant tomato less than 10% irrespective of the rotation sequence. Concerning the Vi, Pf was below the detection level at the end of the rotation in resistant and 3 times Pi in the susceptible. The cumulative yield of grafted crops was 2.83 times higher than that of the ungrafted and the RI in resistant tomato was 7.6%, losing the population's virulence. In the histopathological study, no differences in number of GC per feeding site were observed in watermelon compared to C. amarus, but they were more voluminous and contained higher number of nuclei per GC and per feeding site. Regarding pepper, Avi population did not penetrate resistant rootstock.

Evaluation of the mechanism of action of Bacillus spp. to manage Meloidogyne incognita with split root assay, RT-qPCR and qPCR.

The goal of this research is to determine the mechanism of action of two Bacillus spp. that can manage Meloidogyne incognita population density in cotton. The overall objectives are 1) determine the efficacy and direct antagonistic capabilities of the Bacillus spp. and 2) determine the systemic capabilities of the Bacillus spp. The greenhouse in planta assay indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could manage M. incognita similarly to the chemical standard fluopyram. An in vitro assay determined that B. firmus I-1582 and its extracted metabolites were able to directly manage M. incognita second stage juveniles by increasing mortality rate above 75%. A split root assay, used to determine systemic capabilities of the bacteria, indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could indirectly decrease the nematode population density. Another species, B. mojavensis strain 2, also demonstrated systemic capabilities but was not a successful biological control agent because it supported a high population density in greenhouse in planta assay and in the split root assay. A RT-qPCR assay was used to confirm any systemic activity observed in the split root assay. At 24 hours both B. amyloliquefaciens QST713 and B. firmus I-1582 upregulated one gene involved in the initial stages of JA synthesis pathway but not another gene involved in the later stages of JA synthesis. These results point to a JA intermediate molecule, most likely OPDA, stimulated by the bacteria rather than JA in a short-term systemic response. After 1 week, the Bacillus spp. stimulated a SA-responsive defense related gene. The long-term systemic response to the Bacillus spp. indicates salicylic acid also plays a role in defense conferred by these bacteria. The final assay was a qPCR to determine the concentration of the bacteria on the cotton roots after 24 days. Bacillus amyloliquefaciens QST713 and B. firmus I-43 1582 were able to colonize the root successfully, with the concentration after 24 days not significantly differing from the concentration at inoculation. This study identifies two bacteria that work via systemic resistance and will help aid in implementing these species in an integrated management system.

Fluopyram: Optimal Application Time Point and Planting Hole Treatment to Control Meloidogyne incognita

Research into new nematicides that provide adequate control against root-knot nematodes in a more environment-friendly way is of great interest to vegetable growers. Thus, the effect of fluopyram, a relatively new chemical nematicide, was evaluated against a Swiss population of Meloidogyne incognita in vitro, in soil and as a planting hole treatment for tomato, lettuce and cucumber plants. Fluopyram treatment in vitro revealed LC50 (lethal concentration, 50%) ranging from 2.15–0.04 µmol of fluopyram/L after 1–14 days of exposure. However, some nematodes (visually categorized as dead) were able to recover and infect cucumber plants. Fluopyram’s optimal application time appeared to be up to 1 day after planting, with a significant control effect on M. incognita up to 14 days after planting. A root penetration assay showed that only nematodes that remained in the rhizosphere were controlled by fluopyram. Furthermore, fluopyram planting hole treatments on lettuce, tomato and cucumber plants, successfully controlled M. incognita in the root zone under greenhouse conditions. Overall, this study contributes to an optimized application of fluopyram for the control of M. incognita in vegetable crops, highlighting its effectiveness in soil and showing its limitation to control juveniles that have already invaded the root systems of plants.

Effect of Glomus fasciculatum and induced population of Meloidogyne incognita on uptake of major nutrients by tomato cultivars

Effect of Glomus fasciculatum and induced population of Meloidogyne incognita on uptake of major nutrients by tomato cultivars

Effect of soil sterilants on nematodes, microarthropods and soil mycoflora in tomato under protected conditions

The effect of metham sodium, dazomet and neem cake was observed on plant parasitic and saprophytic nematodes, microarthropods and fungi in tomato under polyhouse conditions. There was significant reduction in the population of Meloidogyne incognita (46.8 -74.8%) and Helicotylenchus (77.7–100.0%) with metham sodium (30, 50 mL per m2) and dazomet (30, 50 g per m2) at the crop harvest. Neem cake was found to be least effective and showed 21.2 and 31.7% reduction in population of M. incognita and Helicotylenchus, respectively. Saprophytic nematodes were also adversely affected by metham sodium and dazomet showing reduction in their population by 46.3–90.9%, whereas in neem cake, decrease in the population of saprophytic nematodes was 46.3%. Microarthropod population in different treatments of metham sodium and dazomet was found to decline from 85.7–100.0%. Six fungi were isolated and out of these, Fusarium sp. was relatively tolerant.

Reproduction potential of Nigerian Meloidogyne spp. and the response of six commercial watermelon cultivars to predominant species

The reproduction potential of nine single-species Meloidogyne populations and 16 mixed-species communities, recovered from watermelon rhizospheres in South-West Nigeria, were determined in roots of tomato (cv. Tropimech) in a glasshouse. The host responses of six commercial watermelon cultivars were also assessed under glasshouse conditions to single-species populations of Meloidogyne incognita, M. javanica and M. enterolobii. Reproduction potential of different Meloidogyne populations and the host response of the cultivars were assessed based on the number of egg masses, final nematode population (Pf), reproduction factor (Rf) and relative susceptibility values (S%). No significant interaction (P < 0.05) existed between replicated reproduction potential experiments for Meloidogyne populations, while a significant interaction (P < 0.05) was apparent between the two host status experiments. Rfs varied in between 4 and 46 in comparing single and mixed community populations of Meloidogyne spp. All watermelon cultivars were susceptible to the predominant single-species populations of Meloidogyne spp.: ‘Charleston Gray’ had the highest Rf (14.7) for M. enterolobii, while ‘Sugar Dragon’ had the lowest (2.1) for M. incognita. The results suggest that cultivars with the lowest Rf and S% for the respective Meloidogyne spp. should be the preferred choice of producers to avoid uncontrolled population build-up of Meloidogyne spp. The data generated from this study provide valuable and useful information to watermelon growers and breeders focusing on root-knot nematode resistance breeding to enable sustainable cultivation of the crop.

Garlic essential oil reduces the population of Meloidogyne incognita in tomato plants

The root-knot nematode Meloidogyne incognita causes losses in tomato production, making new methods/products to control this parasite desirable. Garlic essential oil (GEO) is potentially useful for controlling M. incognita. Here, GEO was obtained by hydrodistillation, dissolved in water and used against M. incognita in vitro. At 63 μg mL−1, this oil was more active against M. incognita eggs and second-stage juveniles (J2) than the nematicide Carbofuran at 173 μg mL−1. The main components of the oil, according to gas chromatography-mass spectrometry analysis, are diallyl trisulphide (66.7%) and diallyl disulphide (21.3%), which presented lethal concentrations to 50% (LC50) J2 equal to 36.2 ± 1.7 and 134.4 ± 19.4 μg mL−1, respectively, while the LC50 for Carbofuran was 151.6 ± 2.1 μg mL−1. When the J2 submerged in a solution of the oil at 250 μg mL−1 were used to infest tomato plants, the number of galls and eggs of M. incognita in the roots were reduced to values statistically equal to those obtained when J2 were submerged in a solution of Carbofuran at 415 μg mL−1. The vapour of the oil was also as active in vitro against M. incognita eggs and J2 as the fumigant nematicide Dazomet. The infectivity and reproduction of M. incognita in tomato plants cultivated in substrate inoculated with eggs of the nematode and treated with 0.2 mL of oil per L of substrate were statistically equal to those observed when the oil was replaced by 0.25 g of Dazomet per L of substrate. These findings confirm the activity of GEO and its components against M. incognita, suggesting its potential as a new fumigant nematicide to control the nematode in tomato plants.

Effects of yeast fermentation broths on the Meloidogyne incognita population in soybean

Root-knot nematodes are pathogenic to a wide range of plants worldwide and can reduce the yield potential of important crops. The objective of this study was to investigate the potential effects of yeast fermentation broths (YFBs) on the hatching of Meloidogyne incognita second-stage juveniles (J2s) in vitro. In addition, application methods of the yeasts for the control of the nematode in soybean were evaluated. Fermentation broths (FBs) of Pichia manshurica CCMA0762, Pichia caribbica CCMA0759, Lachancea thermotolerans CCMA0763, Hanseniaspora opuntiae CCMA0760 and Kodamaea (Pichia) ohmeri CCMA0758 were evaluated in the hatching test in vitro. The same treatments were separately applied to the soil, soil+shoot and shoots of plants inoculated with M. incognita, and the results were compared with those of the control and those from a yeast-based commercial product. L. thermotolerans CCMA0763 and P. caribbica CCMA0759 FBs were selected for evaluation of nematode infection. All YFBs inhibited J2 hatching. The L. thermotolerans FB reduced the number of nematodes in one experiment when applied to soil. The most effective application mode differed by FB type. L. thermotolerans and P. caribbica FBs, when applied to shoots, decreased the number of J2s, sausage-shaped juveniles, adult females and total nematodes at different evaluation times.

Crotalaria and millet as alternative controls of root-knot nematodes infecting okra

The relationship of crops grown in rotation or in succession has increased every day and the use of antagonistic plants and/or non-host plants is one of the most efficient practices of integrated management of nematodes. This study aimed to evaluate the efficiency of crotalaria (Crotalaria spectabilis Roth) and millet [Pennisetum glaucum (L.) Leeke] ‘ADR 300’ in reducing the population of Meloidogyne incognita and M. javanica and in increasing the productivity of okra [Abelmoschus esculentus (L.) Moench] when cultivated in succession. The experiment was conducted in an area cultivating okra (host culture) in rotation, with a history of severe infestation by phytonematoids. The experimental design involved randomized blocks with six treatments and four replicates, with the following treatments: T1, 15 kg.ha-1 of millet seeds; T2, 30 kg.ha-1 of crotalaria; T3, 10 kg.ha-1 of millet + 20 kg.ha-1 of crotalaria; T4, 20 kg.ha-1 of millet + 6 kg.ha-1 of crotalaria; T5, 6 kg.ha-1 of millet + 36 kg.ha-1 of crotalaria; and T6, control. The nematode populations in the soil and roots were evaluated about 60 d after planting okra, and the yield was evaluated at the end of the crop cycle. Simple treatment with millet or crotalaria reduced the nematode population by 61% and 72%, respectively. The millet-crotalaria intercropping treatments reduced the nematode population by up to 85% compared with the control. In terms of productivity, there was an increase of 787 kg.ha-1 in the millet treatment and 2,109 kg.ha-1 in the intercropping treatments. Both the single cultivation of crotalaria or millet and the consortia of crotalaria and millet were effective in controlling the root-knot nematodes, and increased the productivity of okra.

Commercial Formulates of Trichoderma Induce Systemic Plant Resistance to Meloidogyne incognita in Tomato and the Effect Is Additive to That of the Mi-1.2 Resistance Gene.

Meloidogyne is the most damaging plant parasitic nematode genus affecting vegetable crops worldwide. The induction of plant defense mechanisms against Meloidogyne in tomato by some Trichoderma spp. strains has been proven in pot experiments, but there is no information for tomato bearing the Mi-1.2 resistance gene or for other important fruiting vegetable crops. Moreover, Trichoderma is mostly applied for managing fungal plant pathogens, but there is little information on its effect on nematode-antagonistic fungi naturally occurring in soils. Thus, several experiments were conducted to determine (i) the ability of two commercial formulates of Trichoderma asperellum (T34) and Trichoderma harzianum (T22) to induce systemic resistance in tomato and cucumber against an avirulent Meloidogyne incognita population in split-root experiments; (ii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to an avirulent M. incognita population in sterilized soil; and (iii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to a virulent M. incognita population in two suppressive soils in which Pochonia chlamydosporia is naturally present, and the effect of T34 on the level of P. chlamydosporia egg parasitism. Both Trichoderma formulates induced resistance to M. incognita in tomato but not in cucumber. In tomato, the number of egg masses and eggs per plant were reduced by 71 and 54% by T34, respectively. T22 reduced 48% of the number of eggs per plant but not the number of egg masses. T34 reduced the number of eggs per plant of the virulent M. incognita population in both resistant and susceptible tomato cultivars irrespective of the suppressive soil, and its effect was additive with the Mi-1.2 resistance gene. The percentage of fungal egg parasitism by P. chlamydosporia was not affected by the isolate T34 of T. asperellum.

Construction of artificial microRNA expression vectors for inhibition of Minc16281 gene in root-knot nematode Meloidogyne incognita

Effectors have been identified to play a very important role in the parasitism of plant-parasitic nematode. To cope with this type of pathogen, many approaches of silencing genes encoding for effectors have been studied and promise to be an effective tool to create plant varieties resistant to plant-parasitic nematodes. In this study, the Minc16281 gene encoding a pioneer effector with unknown function was determined and cloned from a Meloidogyne incognita population isolated from soybean field (ID: MH315945.1). The nucleotide sequence of this gene showed 97% identity to its homolog in GenBank (ID: JK287445.1) used as the control strain in our research. To generate host-induced gene silencing constructs which can potentially silence the expression of Minc16281 gene, two artificial microRNAs were synthesized based on the miR319a structure of Arabidopsis thaliana and inserted into an expression vector in soybean. These microRNAs can be introduced into soybean to investigate the function of Minc16281 on parasitism of root-knot nematode.

Response of eggplant genotypes to avirulent and virulent populations of Meloidogyne incognita (Kofoid &amp; White, 1919) Chitwood, 1949 (Tylenchida: Meloidogynidae)

Eggplant is widely grown throughout the world. However, some eggplant genotypes are susceptible to Meloidogyne spp., so Solanum torvum (Sw.) is commonly used as a resistant rootstock for root-knot nematodes. Further investigations of resistant sources to root-knot nematodes are still necessary for breeding programs. In this study, a total of 60 eggplant genotypes, including wild sources, wild rootstocks, wild × wild eggplant rootstocks, wild × cultivated eggplant rootstocks, cultivated eggplant rootstocks, pure lines, standard commercial cultivars and commercial hybrids, were tested with avirulent S6 and Mi-1 virulent V14 populations of Meloidogyne incognita (Kofoid & White, 1919) Chitwood, 1949 (Tylenchida: Meloidogynidae) under controlled conditions. The study was conducted in 2016-2017. The seedlings were inoculated with 1000 second-stage juveniles of M. incognita. Plants were uprooted 8 weeks after nematode inoculation, and the numbers of egg masses and galls on the roots and juveniles in the soil of pots were counted. Solanum torvum (Y28) was found to be resistant to S6 and V14 populations of M. incognita. The remaining genotypes were susceptible to both populations . These results could be used for breeding and management purposes for the control of root-knot nematode.

Effect of fluensulfone and fluopyram on the mobility and infection of second-stage juveniles of Meloidogyne incognita and M. javanica.

Fluensulfone and fluopyram are new nematicides whose mode of action is not fully understood. Differences in the nematicidal activity of these compounds among two Meloidogyne incognita populations and a Meloidogyne javanica population, and the effect of sublethal exposure to the nematicide on their infection process were studied in vitro. The M. incognita populations were more sensitive to fluensulfone than M. javanica, whereas M. javanica was more sensitive to fluopyram. A more than 10-fold difference in median lethal concentration (LC50 ) was observed between the M. incognita populations after 17-h exposure to fluensulfone. Exposure of M. incognita and M. javanica to 4 mg L-1 fluopyram for 48 h resulted in irreversible immobilization, whereas lower concentrations or 17-h exposure to fluopyram caused reversible immobilization. Pre-exposure of M. javanica to fluensulfone at sublethal concentrations reduced the number of juveniles attracted to root tips and caused smaller galls. Pre-exposure to fluopyram delayed the nematodes' attraction. Presence of fluopyram in a Pluronic gel at concentrations that immobilized the nematodes in water showed no or only slight inhibition of the nematodes' attraction to root tips and gall formation. Different sensitivities to nematicides were observed among Meloidogyne species and populations. Sublethal exposure to fluensulfone reduced nematode attraction to root tips and infection. Pluronic gel negatively affected nematicidal activity, especially for fluopyram. © 2019 Society of Chemical Industry.

Phytotoxic and nematicide evaluation of Croton ehrenbergii (Euphorbiaceae).

Within its natural habitat, Croton ehrenbergii exhibits an innate defense mechanism that is not seen in other plants; it grows unharmed amidst predators and nature, while other species perish. In light of its capacity for defense, C. ehrenbergii was evaluated to better understand the scope of its phytotoxic and nematicide properties. To assess this, fractions obtained by bipartition of a hydro-alcoholic extract, and l-quebrachitol, the main constituent of C. ehrenbergii, were evaluated on Lactuca sativa (dicotyledon) and Lolium perenne (monocotyledon) seeds. Additionally, bipartition fractions and l-quebrachitol were evaluated on a population of Meloidogyne incognita for their nematicide activity. From this phytochemical research, l-quebrachitol (1), phenylalanine (2), trans-4-hydroxy-N-methylproline (3) and the flavonoids: kaempferol (4), tiliroside (5), nicotiflorine (6) and rutin (7) were identified by spectroscopic analysis. Both methanol and hexane fractions from aerial parts of the plant inhibited the germination and elongation of roots and stems in L. sativa, but not in Lolium perenne, showing that these fractions mostly inhibit the dicotyledon species used in this research. l-Quebrachitol showed slightly higher seed germination inhibition for Lolium perenne in comparison with L. sativa. Three of the fractions evaluated showed nematicide activity against Meloidogyne incognita larvae (J2) at the 48 h benchmark, compared with carbofuran. l-Quebrachitol shows higher mortality after 48 h exposure at a lower concentration than carbofuran. A variety of compounds were isolated from this research, some were common within the Croton genus (4-7), whereas others were not (1-3). This is the first phytochemical, phytotoxic and nematicide report on C. ehrenbergii. Methanol and hexane fractions from the aerial parts of C. ehrenbergii and l-quebrachitol could be used as alternative natural herbicides, predominantly against dicotyledon weed seeds. All fractions had a good mortality percentage against J2 Meloidogyne incognita larvae. © 2019 Society of Chemical Industry.

Virulence of Meloidogyne incognita populations and Meloidogyne enterolobii on resistant cucurbitaceous and solanaceous plant genotypes

Root-knot nematodes (Meloidogyne spp.) cause extensive damage to tomato and cucurbit crops in protected cultivation systems. An environmentally benign solution for nematode control is the use of plant resistance that mitigates yield losses and reduces the Meloidogyne population in the soil. A collection of three tomato and six cucumber rootstocks was tested for resistance against eight Meloidogyne incognita populations (with different levels of virulence) in comparison with the susceptible variety Moneymaker and the resistant varieties Phantasia or Oskar. In addition, M. enterolobii was included in these experiments to evaluate the response of the tomato and cucumber plant genotypes. Tests were both conducted in a greenhouse or growth chamber and evaluated after completion of one reproduction cycle. The correlation of plant responses to Meloidogyne populations from the different experiments showed significant relationships for 13 and 20 out of 36 combinations for the parameters gall index and number of egg masses per root system, respectively. In particular, two a-virulent reference populations showed significant positive relationships for both parameters, resulting in the same ranking of tested plant genotypes across test systems. Conversely, plant genotypes showed different responses when inoculated with virulent populations of M. incognita or M. enterolobii. Some of the plant genotypes tested showed potential for use in Meloidogyne spp. management strategies. However, cucumber plant genotypes seemed more suitable than tomato genotypes. Furthermore, some of the tested cucumber rootstocks were less sensitive when challenged with M. enterolobii in pot experiments.