Meloidogyne Incognita Second-stage Juveniles Research Articles

Nematicidal trans-Anethole Blends Paralyzing Meloidogyne incognita

Nematodes have a negative impact on crop production and yield. The use of synthetic formulations to control plant parasitic nematodes carries both environmental and human health risks. As these agrochemicals are gradually being phased out, recent research has been focused on finding more environmentally friendly, plant-based alternatives. This study aims to investigate the effectiveness of botanicals, used alone or in artificial blends, in paralyzing Meloidogyne incognita second-stage juveniles (J2s) immersed in test solutions or exposed to vapors. We tested thymol, trans-anethole, and two lavender essential oils, referred to as LEOA and LEOB, which vary in their flower and stem compositions. We also employed in our study Melia azedarach aqueous extract (MWE), already proven to have considerable nematicidal activity. According to our findings, all treatments used individually exhibited considerable efficacy, even LEOA and LEOB first reported herein. In addition, all blends exhibited significant synergism, and the best-performing were trans-anethole/thymol, being synergic to paralyzing J2s for up to two days, and trans-anethole/LEOB as well as trans-anethole/MWE, provoking irreversible paralysis since the first day of J2 immersion in test solutions. Most importantly, the blend of trans-anethole with LEOA displayed the best effective synergism against M. incognita both for immersion and fumigation methods. Lastly, the chemical composition analysis displayed linalyl acetate and β-linalool as the major components of LEOA and β-linalool and eucalyptol as the major components of LEOB.

Discovery and Mechanism of a Nematicide Candidate (W3): A Novel Amide Compound Containing a Cyclopropyl Moiety.

To find novel nematicides, we screened the nematicidal activity of compounds in our laboratory compound library. Interestingly, the compound N-((1R,2R)-2-(2-fluoro-4-(trifluoromethyl)phenyl)cyclopropyl)-2-(trifluoromethyl)benzamide (W3) showed a broad spectrum and excellent nematicidal activity. The LC50 values of compound W3 against second-stage juveniles of Bursaphelenchus xylophilus (B. xylophilus), Aphelenchoides besseyi, and Ditylenchus destructor are 1.30, 1.63, and 0.72 mg/L, respectively. Nematicidal activities of compound W3 against second-stage juveniles of Meloidogyne incognita were 87.66% at 100 mg/L. Meanwhile, compound W3 can not only observably inhibit the feeding, reproduction, and egg hatching of B. xylophilus but can also effectively promote the oxidative stress adverse reactions of nematodes and cause intestinal damage. Compound W3 can promote the production of MDA and inhibit the activities of defense enzymes SOD and GST in B. xylophilus. Compound W3 can affect the transcription of genes involved in regulating the tricarboxylic acid cycle in nematodes, resulting in weakened nematode respiration and reduced nematode activity and even death. In addition, compound W3 had good inhibitory activity against five pathogenic fungi. Among them, the EC50 of compound W3 against Fusarium graminearum was 8.4 mg/L. In the future, we will devote ourselves to the toxicological and structural optimization research of the candidate nematicide W3.

Effect of short-term growth of mung bean and its incorporation with nitrogen fertiliser on the density of the root-knot nematode, Meloidogyne incognita, in soil

Summary Soybean is attacked by multiple plant-parasitic nematodes and the major ones are soybean cyst nematode (SCN) and root-knot nematodes. Our previous study reported that 2 weeks growth of mung bean and its soil incorporation markedly reduced SCN density in soil via hatching stimulation by mung bean residue. This study aimed: i) to evaluate whether incorporation of mung bean in combination with N fertiliser decreased the density of Meloidogyne incognita, which attacks both soybean and mung bean; and ii) to determine the direct effect of ammonium solutions on M. incognita J2 and hatching. The results showed that after the growth period of mung bean for 2 weeks and 4 weeks of its incorporation, the density of M. incognita was significantly reduced by 54 and 72% in the mung bean treatment with and without N fertiliser (140 mg N (kg soil)−1), respectively, compared with the control. Soil urease activity was significantly higher in the mung bean with N fertiliser than in the control. Meloidogyne incognita second-stage juveniles were less mobile in NH4Cl solutions with 100-250 mg N l−1 than in 0 mg N l−1. Moreover, NH4Cl solutions with 140 mg N l−1 and 250 mg N l−1 significantly inhibited the hatching of M. incognita. This study demonstrated that 2 weeks growth of mung bean may be a potential trap crop for M. incognita and N metabolism might be involved to a certain extent in the suppression of M. incognita.

Sulfoxide-Containing Bisabolane Sesquiterpenoids with Antimicrobial and Nematicidal Activities from the Marine-Derived Fungus Aspergillus sydowii LW09.

Phytopathogens, such as phytopathogenic bacteria, fungi, and nematodes, have caused great losses of crops every year, seriously threatening human health and agricultural production. Moreover, marine-derived fungi are abundant sources of structurally unique and bioactive secondary metabolites that could be potential candidates for anti-phytopathogenic drugs. One new sulfoxide-containing bisabolane sesquiterpenoid aspersydosulfoxide A (1) and nine known analogues (2-10) were isolated from the marine-derived A. sydowii LW09. The absolute configuration of the sulfur stereogenic center in 1 was determined by electronic circular dichroism (ECD) calculations. Compound 5 showed inhibition activity against Pseudomonas syringae, with a minimum inhibitory concentration (MIC) value of 32 μg/mL, whereas, compounds 2, 7, and 8 showed antibacterial activities toward Ralstonia solanacarum, with the same MIC value at 32 μg/mL. Meanwhile, compounds 3, 7, and 8 inhibited the fungal spore germination of Fusarium oxysporum, with the half maximal effective concentration (EC50) values of 54.55, 77.16, and 1.85 μg/mL, respectively, while compounds 2, 3, 7, and 8 inhibited the fungal spore germination of Alternaria alternata, which could be induced by vacuolization of germ tubes, with EC50 values of 34.04, 44.44, 26.02, and 46.15 μg/mL, respectively. In addition, compounds 3, 7, and 8 exhibited nematicidal activities against Meloidogyne incognita second-stage juveniles (J2s). In addition, compound 8 possessed the strongest nematicidal activity of nearly 80% mortality at 60 h with the half lethal concentration (LC50) values of 192.40 μg/mL. Furthermore, compounds 3, 7, and 8 could paralyze the nematodes and then impair their pathogenicity.

Manejo de nematoides-de-galha em quiabeiro por meio de enxertia em vinagreira-roxa e vinagreira-flor-de-veludo

Abstract The objective of this work was to evaluate the performance of okra grafted onto Hibiscus spp. in the presence and absence of three root knot nematode species. The experimental design was completely randomized in a 4x4 factorial arrangement with ten replicates. The first factor consisted of the following four rootstocks: kenaf (Hibiscus cannabinus), false roselle (Hibiscus acetosella), self-grafted, and non-grafted. The second factor was the inoculation of 5,000 eggs and second-stage juveniles of Meloidogyne incognita, Meloidogyne javanica, and Meloidogyne enterolobii in okra plants, plus an uninoculated control. Vegetative development, agronomic performance, and nematode reproduction were evaluated. The grafting of okra onto Hibiscus spp. in the presence of root-knot nematodes provided a greater plant height, scion length, fresh shoot mass, number of fruits, and yield, when compared with self-grafted and non-grafted plants. The averages of the root-knot nematode reproduction factor were low in the plants grafted onto Hibiscus spp., indicating that grafting in the presence of root-knot nematodes is capable of maintaining okra vegetative development and yield.

Fabrication of zinc oxide nanorods using plant latex serum as a green matrix for the sustainable management of root-knot nematodes

In this study, zinc oxide nanorods were fabricated using Synadenium grantii latex serum (Sg-ZnO Nrs) as a green matrix. The characterization of Sg-ZnO Nrs was carried out with UV–vis spectroscopy, XRD, FTIR, and FE-SEM. The fabricated Sg-ZnO Nrs was tested for nematicidal activity against second-stage juveniles of Meloidogyne incognita (J2s) in in vitro and pot experiments. Furthermore, the effect of Sg-ZnO Nrs on seed germination was also examined using tomato seeds. The Sg-ZnO Nrs was highly active against J2s with an LC50/48h value of 111.01 µg/mL. In pot experiments, 300 and 400 µg/mL of Sg-ZnO Nrs were most effective in disease control and plant growth parameters. In addition, Sg-ZnO Nrs showed a substantial growth-promoting effect on tomato seed germination and seedling length at 300 and 400 µg/mL concentrations, and concurrently, it induced 97.42 and 100 % J2s mortality in in vitro conditions, respectively.

Differential response of cowpea towards the CuO nanoparticles under Meloidogyne incognita stress

The application of nanoparticles as potent nematicides along with the plant growth-promoting effects is quite intriguing to meet the need for an alternative management strategy for nematode management. Here we reported the nematicidal effects of synthesized Copper oxide nanoparticles (CuO) against Meloidogyne incognita second-stage juveniles (J2S) under in vitro and in planta conditions at different concentrations. Scanning Electron Micrograph of CuO nanoparticles treated J₂S revealed the distorted, crinkled cuticle in comparison to control J₂S. CuO nanoparticles in graded concentrations (50, 100 and 200 ppm) applied concomitantly, three days before and after the nematode inoculation was assessed in terms of morphology, yield and biochemical attributes of infected Cowpea (Vigna unguiculata L. Gomti.). In planta, trials revealed that the application of CuO nanoparticles before the nematode inoculation at 100 ppm concentration exhibited healthier growth attributes besides concurrent reduction in nematode parameters in comparison to plants treated with M. incognita.

Volatile fatty acids from whey volatilome as potential soil fumigants to control Meloidogyne incognita

Organic residues emit volatile organic compounds (VOCs) that are toxic to plant-parasitic nematodes (PPNs). In this study, we demonstrated that whey produced by cow milk emit VOCs that are toxic to Meloidogyne incognita second-stage juveniles (J2), causing immobility above 80% and significant (P < 0.05) mortality compared to controls. The analysis of the volatilome done by gas chromatography coupled with mass spectrometry revealed 28 compounds, predominantly carboxylic acids and esters. Four of those volatile fatty acids (VFAs), namely acetic acid, octanoic acid, ethyl octanoate, and isovaleric acid, were chosen to further studies. The four tested VFAs were toxic to M. incognita J2, with lethal concentration values required to kill 50% of the nematode population (LC50), ranging from 134.30 to 236.08 μg mL−1. However, on eggs, only acetic acid and ethyl octanoate were consistent with J2 hatch inhibition, reaching 80% at a concentration of 1000 μg mL−1. In a greenhouse assay, when the VFAs were applied as soil fumigant, M. incognita infectivity and reproduction were significantly (P < 0.05) reduced compared to the negative control (water). Among them, ethyl octanoate application reduced (P < 0.05) the number of eggs to the level of the commercial fumigant dazomet. Overall, the volatile compounds released by whey were toxic to M. incognita J2 and contained a great diversity of molecules. Among the VFAs, ethyl octanoate stood out and showed the potential to be used in future field studies.

Chemotaxis response of Meloidogyne incognita to volatiles and organic acids from root exudates

Chemotaxis plays an important role in food-finding, mate-finding, response to host plants and other aspects of nematode interactions. In this study, chemotaxis responses of Meloidogyne incognita second-stage juveniles (J2) to seven plant hosts were investigated. Chemotaxis volatiles from root exudates were analyzed by gas chromatography-mass spectrometry, from which four attractive compounds were identified as the tridecane, 1-docosene, 1-octadecene and 2-hexyl-1-decanol. 1-docosene was distributed in root exudates of all seven plants, while the other compounds were found only in some root exudates. In addition, organic acids commonly found in plant root exudates were screened. Among the 16 types of organic acids, six organic acids could attract J2 of M. incognita. Malic acid, oxalic acid and lactic acid were found to demonstrate chemotactic effect on M. incognita J2 and were distributed differently in the seven plants. These results indicate that volatiles and organic acids secreted from different plants possess the ability to attract the J2 of M. incognita. This study provides insight into the signaling mechanism between root-knot nematodes and host plants, which may thus help develop more effective biological control methods.

Morphometric and total protein responses in Meloidogyne incognita second-stage juveniles to Nemafric-BL phytonematicide

After hatch, second-stage juveniles (J2) of root-knot (Meloidogyne species) nematodes could spend at least 12 weeks in soil solutions searching for penetration sites of suitable host plants. The external covering of nematodes, the cuticle, consists of various layers that contain glycoproteins, lipids, soluble proteins (collagens) and insoluble proteins (cuticulins). Generally, cucurbitacins are lipophilic, but there is scant information on how cuticular proteins relate to these complex terpenoids. A study was conducted to investigate the nature and extent of damage post-exposure of J2 to a wide range of Nemafric-BL phytonematicide concentrations. Post-72 h exposure to Nemafric-BL phytonematicide, nematode morphometrics versus phytonematicides exhibited either negative quadratic, positive quadratic, or negative linear relations, with the models explained by significant (P < 0.05) associations (R-squared). Similarly, total proteins versus phytonematicide exhibited significant negative quadratic relations. The principal component analysis indicated that concentration level of 2–4% of Nemafric-BL phytonematicide have the highest impact on the morphometric changes of J2. In conclusion, the nature and extent of damage suggested that Nemafric-BL phytonematicide was highly nematicidal as opposed to being nematostatic, thereby explaining its potent suppressive effects on nematode population densities.

Chemotactic responses of Brugia pahangi infective third-stage larvae to tris(hydroxymethyl)aminomethane-related compounds and amino acids.

Since the exogenous compound tris(hydroxymethyl)aminomethane (Tris) showed a potent chemoattractant activity for Brugia pahangi infective third-stage larvae (L3), it was assumed that, in natural infection to a host, filarial L3 can be expected to recognize an endogenous Tris-related compound. In addition, a few amino acids have been identified as water-soluble attractants for second-stage juveniles of Meloidogyne incognita, a plant parasitic nematode. Therefore, the present study assesses the in vitro chemotactic responses of B. pahangi L3 to Tris-related compounds and amino acids using an agar-plate assay. Among Tris-related compounds, 2-amino-1,3-propanediol (APD) and 2-amino-2-methyl-1,3-propanediol (AMPD) exhibited a potent chemoattractant activity for filarial L3 at a level similar to Tris. Furthermore, arginine (Arg) was identified as a potent attractant for filarial L3 among amino acids. In addition, filarial L3 were attracted to Arg, APD and AMPD in mild alkaline conditions rather than acidic conditions. The chemoattractant activity of the three compounds for filarial L3 was observed in concentrations between 6.3 and 200 mm. This is the first report to demonstrate that Arg, APD and AMPD are potent chemoattractants for B. pahangi L3. Endogenous Arg and APD, in particular, may be involved in the regulation of the chemotactic behaviour of filarial L3 in the infection to a host. The present results will help to elucidate the mechanism of filarial skin-penetrating invasion of a host.

Τhe Nematicidal Potential of Bioactive Streptomyces Strains Isolated from Greek Rhizosphere Soils Tested on Arabidopsis Plants of Varying Susceptibility to Meloidogyne spp.

A total of 461 indigenous Streptomycetes strains recovered from various Greek rhizosphere habitats were tested for their bioactivity. All isolates were examined for their ability to suppress the growth of 12 specific target microorganisms. Twenty-six were found to exert antimicrobial activity and were screened for potential nematicidal action. S. monomycini ATHUBA 220, S. colombiensis ATHUBA 438, S. colombiensis ATHUBA 431, and S. youssoufensis ATHUBA 546 were proved to have a nematicidal effect and thus were further sequenced. Batch culture supernatants and solvent extracts were assessed for paralysis on Meloidogyne javanica and Meloidogyne incognita second-stage juveniles (J2). The solvent extracts of S. monomycini ATHUBA 220 and S. colombiensis ATHUBA 438 had the highest paralysis rates, so these Streptomycetes strains were further on tested for nematodes’ biological cycle arrest on two Arabidopsis thaliana plants; the wild type (Col-0) and the katanin mutant fra2, which is susceptible to M. incognita. Interestingly, S. monomycini ATHUBA 220 and S. colombiensis ATHUBA 438 were able to negatively affect the M. incognita biological cycle in Col-0 and fra2 respectively, and increased growth in Col-0 upon M. incognita infection. However, they were ineffective against M. javanica. Fra2 plants were also proved susceptible to M. javanica infestation, with a reduced growth upon treatments with the Streptomyces strains. The nematicidal action and the plant-growth modulating abilities of the selected Streptomycetes strains are discussed.

Synergism of citral from Cymbopogon citratus essential oil and undecan-2-one against Meloidogyne incognita

Summary The nematicidal activity of the essential oil of Cymbopogon citratus and its main components were studied. During in vitro assays with Meloidogyne incognita second-stage juveniles (J2), the oil showed an LC50 of 166 μg ml−1. In vivo assays that exposed J2 to the LC50 oil concentration significantly reduced galls and eggs on tomato roots. According to gas chromatography-mass spectrometry analyses, the main components of the essential oil were geranial (42.7%) and neral (33.0%). The combination of these two isomers, known as citral, had an enhanced nematicidal activity at low concentrations as shown by in vitro tests through a synergistic interaction with undecan-2-one. In assays with tomato plants inoculated with M. incognita J2, the combination of citral (600 μg ml−1) and undecan-2-one (300 μg ml−1) showed a high reduction in the number of galls (63.4%) and eggs (56.3%) in relation to Tween 80® control. The citral/undecan-2-one combination showed a synergistic nematicidal activity against M. incognita during in vitro and in vivo assays.

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.

Toxicities of 4,5-Dihydroisoxazoles Against Root-Knot Nematodes and in Silico Studies of Their Modes of Action.

The present work sought to contribute to the development of new nematicides. Benzaldehydes were initially converted to nitrile oxides that underwent 1,3-dipolar cycloaddition reactions with methyl acrylate to generate 4,5-dihydroisoxazoles. In in vitro tests, methyl 3-phenyl-4,5-dihydroisoxazole-5-carboxylate (1) and methyl 3-(4-chlorophenyl)-4,5-dihydroisoxazole-5-carboxylate (4) increased the mortality of Meloidogyne exigua and Meloidogyne incognita second-stage juveniles (J2). Compounds 1 and 4 presented necessary concentrations of 398 and 501 μg mL-1, respectively, to kill 50% of M. incognita J2 (LC50 values), while the value for carbofuran (positive control) was 168 μg mL-1. In in vivo tests, compounds 1 and 4 reduced the number of M. incognita galls in tomato roots by 70 and 40%, respectively, and the number of eggs by 89 and 44%. Using an in silico approach, we showed that compounds 1 and 4 were toxic to the nematodes by binding to the allosteric binding sites of the agonist-binding domains of the nematode nicotinic acetylcholine receptors. These results opened up possibilities for further investigations aimed at developing novel commercial nematicides.

Short-Term Effects of Sublethal Doses of Nematicides on Meloidogyne incognita.

Meloidogyne species are one of the most important groups of plant-parasitic nematodes globally because of their ability to damage most cultivated plants. Although they are widespread and economically important, there are limited control measures to combat these nematodes. New nonfumigant nematicides have been discovered that have the potential to be widely utilized for the management of plant-parasitic nematodes. Because of the longer half-lives in soil and lower toxicity of new nematicides compared with traditional fumigant and nonfumigant nematicides, understanding how nematodes respond to sublethal doses of nematicides is imperative to understanding whether nematicide resistance has the potential to develop. Characterizing responses of nematodes to sublethal doses will provide the foundation for future work, such as gene expression studies. In this study, the nematicides oxamyl (Vydate), fluazaindolizine (Salibro), fluensulfone (Nimitz), and fluopyram (Velum), were evaluated to understand how sublethal doses affect the fecundity and mobility of Meloidogyne incognita second-stage juveniles (J2). Using a microwell assay system, dose-response curves for each nematicide were established for M. incognita J2. Fluopyram was the most toxic nematicide, with effective doses up to 230 times lower than that of other nematicides. The other nematicides had predicted ED50 values (effective doses that resulted in 50% of the population becoming inactive) of 89.4, 131.7, and 180.6 ppm for oxamyl, fluensulfone, and fluazaindolizine, respectively. The 24-h ED50 of each nematicide was then used in both motility and infectivity assays. The motility and activity of M. incognita J2 exposed to ED50 doses of fluazaindolizine and fluensulfone was significantly reduced, with nematodes initially being motile but eventually becoming inactive. However, the motility of M. incognita J2 exposed to ED50 doses of fluopyram and oxamyl was not different from a water control. In a pot assay, M. incognita J2 exposed to ED50 doses of fluazaindolizine, oxamyl, and fluensulfone were unable to reproduce on tomato, with reproduction factors (RF = final population density/initial population density) of 0 to 0.03. Fluopyram did not reduce reproduction of M. incognita, with a mean RF of 38.7 ± 4.5, which was similar to the RF of 46.3 ± 4.6 for the water control. This study is the first comprehensive evaluation of M. incognita activity, motility, and fecundity after exposure to the traditional nematicide, oxamyl, as well as three new nematicides, fluazaindolizine, fluopyram, and fluensulfone.

Characterisation of the effects on proteases of Heterodera glycines and Meloidogyne incognita second-stage juveniles by inhibitors obtained from cysts of H. glycines

SummaryThe protease inhibitor component ofHeterodera glycinescyst contents was explored using a battery of peptide substrates andH. glycinesandMeloidogyne incognitasecond-stage juveniles as enzyme sources. Protease inhibitors were prepared by heat-denaturingH. glycinescyst-egg extract (hHglCE), which was used in all inhibition exploration. Eight substrates targeting four endoprotease groups (aspartic, cysteine, metallo- and serine proteases) revealed that protease inhibition by hHglCE varied significantly betweenH. glycinesandM. incognitawith seven of the eight substrates. Only cysteine protease activity was inhibited equally betweenH. glycinesandM. incognita. Aspartic protease activity was inhibited more strongly inH. glycinesand serine protease activity was inhibited more strongly inM. incognita. Digestion of five matrix metalloprotease (MMP) substrates was inhibited more strongly inH. glycines(two substrates) andM. incognita(three substrates). These variations were particularly intriguing given the potential association of MMP proteases with developing embryos. Inhibition of digestion of nematode FMRFamide-like peptides (FLPs) showed less variation between nematode species than the targeted substrates, but inhibition did vary significantly across substrates within each species. Digestion of FLP-6 was the least affected by hHglCE but was inhibited significantly more inM. incognitathan inH. glycines. Residue differences between two FLP-14 sequences significantly affected inhibition of FLP-14 digestion in bothH. glycinesandM. incognita. RP-HPLC fractionation of hHglCE clearly demonstrated the presence of high (Fr No.5) and low (Fr No.14) polarity inhibitor components. Potency of inhibition ofM. incognitaserine protease activity, based upon IC50values (1.68 and 2.78 hHglCEeq reaction−1for Fr No.5 and Fr No.14, respectively), was reduced significantly from unfractionated hHglCE (IC50 = 0.61), suggesting inhibitor dilution, loss of component synergy, or both, due to fractionation.

24-Epibrassinolide reduces stress in nematode-infected tomato (Solanum lycopersicum L.) plants cultured in vitro

24-Epibrassinolide (EBL) is considered the most probable brassinosteroid (BR) candidate that could be used for practical application in agriculture. EBL-induced stress-protective properties were evaluated in in vitro-grown tomato (Solanum lycopersicum L.) varieties Pusa Ruby (susceptible to nematodes) and PNR-7 (resistant to nematodes) during nematode pathogenesis. Sterilized tomato seeds treated with 10−11, 10−9, or 10−7 M EBL and germinated in vitro were inoculated with second-stage juveniles of Meloidogyne incognita [(Kofoid and White) Chitwood]. Whole plant analyses of morphological and biochemical parameters 7 d after inoculation showed significant improvements in plant growth and development for both varieties and a highly significant reduction in the number of galls in the susceptible variety. Increased specific activities of antioxidative enzymes (catalase, ascorbate peroxidase, glutathione reductase, glutathione peroxidase, guaiacol peroxidase, and superoxide dismutase) were observed in EBL-treated seedlings of both varieties, but increases were higher in the resistant variety. A highly significant increase in antioxidants (ascorbic acid content, total flavonoid content, total glutathione content, and total phenolic content) was observed in EBL-treated Pusa Ruby seedlings, whereas in PNR-7, significant increases were found except for total flavonoid content, which increased non-significantly. Confocal microscopic images showed amelioration of stress in roots of EBL-treated seedlings as indicated by the decrease in level of green fluorescence in them as compared to untreated and nematode-inoculated roots.

Confirmation of bioactivities of active ingredients of nemarioc-AL and nemafric-BL phytonematicides

ABSTRACTNemarioc-AL and Nemafric-BL phytonematicides consistently reduced populations of plant-parasitic nematodes. The contribution of juvenile hatch inhibition to the overall reduction of the nematode numbers by the two phytonematicides, with cucurbitacin A and B as active ingredients, respectively, remains undocumented. The objectives of this study were to examine (i) the response of Meloidogyne incognita second-stage juveniles (J2) hatch to increasing concentration of cucurbitacins A and B, (ii) the potential saturation of J2 hatch when exposed to cucurbitacins for extended incubation periods, (iii) the minimum inhibition concentration for J2 hatch and (iv) the reversibility of J2 hatch inhibition.. Eggs of M. incognita were exposed to a series of purified cucurbitacin A and B concentrations over five incubation periods of 24, 48, 72 h and extended incubation periods of 7 and 10 days. Methanol-dissolved cucurbitacin A and B were each diluted and pipetted into well-plates making 11 concentrations, ranging from 0.0 to 2.5 µg.ml−1 water solvent. Juvenile counts were made after 24, 48 and 72 h, with those for saturation assessed at 7 and 10 days. Thereafter, treatments were diluted five times, incubated again for 5 days and counted to establish reversibility of J2 hatch inhibition. In all incubation periods, treatment effects were highly significant (P ≤ 0.01), with J2 hatch and cucurbitacin concentrations exhibiting quadratic relations. Minimum inhibition concentrations of the two cucurbitacins were between 1.13 and 1.40 µg.ml−1. Treatment effects for reversibility to J2 hatch inhibition were not significant (P > 0.05). In conclusion, J2 hatch inhibition could be one of the waysthrough which the two phytonematicides reduced population densities of Meloidogyne species.

In vitro evaluations to determine the effect of Bacillus firmus strains on the motility of Meloidogyne incognita second-stage juveniles

Eco-friendly control strategies, such as biological agents containing Bacillus firmus, are known to adversely impact the biology of Meloidogyne incognita and other nematode pests that damage agricultural crops. The efficacy of two isolated strains as well as one reference strain was evaluated for their effect on M. incognita second-stage juvenile (J2) motility. All three B. firmus strains successfully reduced J2 motility, with the reference strain being superior. Non-cultured cell-free products of the isolated strains inhibited J2 motility only between 3 and 7 % compared to the tap-water controls, respectively, and compared to up to 42 % by their cultured, cell-free water filtrate counterparts. The latter range was also recorded for the 100 % cultured, cell-free suspension concentration of the reference strain. The efficacy of cell suspensions of the two isolated strains were low (7-19 %) compared to the 100 % achieved by the reference strain. Although secondary compounds of the two isolated B. firmus strains may contribute towards disrupting the movement and host finding abilities of J2, they had no pronounced effects on J2 motility inhibition.