Sensitivity of Meloidogyne javanica and Tylenchulus semipenetrans to Isothiocyanates in Laboratory Assays

Glucosinolate Diversity Analysis in Choy Sum (Brassica rapa subsp. chinensis var. parachinensis) Germplasms for Functional Food Breeding

The aim of this study was to analyze glucosinolates (GSLs) in germplasm that are currently conserved at the RDA-Genebank. The analysis focused on the glucosinolate diversity among the analyzed germplasms, with the goal of identifying those that would be most useful for future breeding efforts to produce nutritionally rich Choy sum plants. In total, 23 accessions of Choy sums that possessed ample background passport information were selected. On analyzing the glucosinolate content for 17 different glucosinolates, we observed aliphatic GSLs to be the most common (89.45%) and aromatic GSLs to be the least common (6.94%) of the total glucosinolates detected. Among the highly represented aliphatic GSLs, gluconapin and glucobrassicanapin were found to contribute the most (>20%), and sinalbin, glucoraphanin, glucoraphasatin, and glucoiberin were detected the least (less than 0.05%). We identified one of the accessions, IT228140, to synthesize high quantities of glucobrassicanapin and progoitrin, which have been reported to contain several therapeutic applications. These conserved germplasms are potential bioresources for breeders, and the availability of information, including therapeutically important glucosinolate content, can help produce plant varieties that can naturally impact public health.

Bio-Management of Root-Knot Nematodes on Cucumber Using Biocidal Effects of Some Brassicaceae Crops

Biofumigant and crop sequencing are effective and safe control system activators that maintain soil fertility and reduce pest populations. The study goals were to find new pesticide-free therapies for root-knot nematode management on cucumbers to maintain high yields and protect the environment and human health. In 2018 and 2019, the research employed a fully randomized block design under field conditions with five treatments and control: two bio- fumigants, cultivation of cucumber after broccoli plantlets incorporation (BPI) and radish plantlets incorporation (RPI), two crop sequence treatments (cultivation after broccoli (BCS) and radish (RCS), and nematicide treatment). Cucumber cultivation after BPI treatment exhibited the best horticultural traits, which reflected positively on early and total productivity. The increased yield was gained by suppressing all nematode parameters, the number of nematode larvae, galls, and egg masses, as well as egg hatching reduction. The most effective biocides, total phenols, myrosinase activity, total glucosinolates (GSLs), and isothiocyanates (ITCs) in brassica crops were estimated for their pesticide properties. The highest amount was released with BPI treatment, compared to adult plants and radish in its two stages. The bio-managed treatments revealed superior effectiveness compared to nematicide application and control to suppress the nematode population while enhancing cucumber growth and production.

A Review of the Potency of Plant Extracts and Compounds from Key Families as an Alternative to Synthetic Nematicides: History, Efficacy, and Current Developments

The global nematicides market is expected to continue growing. With an increasing demand for synthetic chemical-free organic foods, botanical nematicides are taking the lead as replacements. Consequently, in the recent years, there have been vigorous efforts towards identification of the active secondary metabolites from various plants. These include mostly glucosinolates and their hydrolysis products such as isothiocyanates; flavonoids, alkaloids, limonoids, quassinoids, saponins, and the more recently probed essential oils, among others. And despite their overwhelming potential, variabilities in quality, efficacy, potency and composition continue to persist, and commercialization of new botanical nematicides is still lagging. Herein, we have reviewed the history of botanical nematicides and regional progresses, the potency of the identified phytochemicals from the key important plant families, and deciphered some of the impediments involved in standardization of the active compounds in addition to the concerns over the safety of the purified compounds to non-target microbial communities.

Deciphering the Behavioral Response of Meloidogyne incognita and Fusarium oxysporum Toward Mustard Essential Oil

Environmental concerns related to synthetic pesticides and the emphasis on the adoption of an integrated pest management concept as a cardinal principle have strengthened the focus of global research and development on botanical pesticides. A scientific understanding of the mode of action of biomolecules over a range of pests is key to the successful development of biopesticides. The present investigation focuses on the in silico protein-ligand interactions of allyl isothiocyanate (AITC), a major constituent of black mustard (Brassica nigra) essential oil (MEO) against two pests, namely, Meloidogyne incognita (Mi) and Fusarium oxysporum f. sp. lycopersici (Fol), that cause severe yield losses in agricultural crops, especially in vegetables. The in vitro bioassay results of MEO against Mi exhibited an exposure time dependent on the lethal concentration causing 50% mortality (LC₅₀) values of 47.7, 30.3, and 20.4 μg ml^-1 at 24, 48, and 72 h of exposure, respectively. The study revealed short-term nematostatic activity at lower concentrations, with nematicidal activity at higher concentrations upon prolonged exposure. Black mustard essential oil displayed excellent in vitro Fol mycelial growth inhibition, with an effective concentration to cause 50% inhibition (EC₅₀) value of 6.42 μg ml^-1. In order to decipher the mechanism of action of MEO, its major component, AITC (87.6%), which was identified by gas chromatography-mass spectrometry (GC-MS), was subjected to in silico docking and simulation studies against seven and eight putative target proteins of Mi and Fol, respectively. Allyl isothiocyanate exhibited the highest binding affinity with the binding sites of acetyl cholinesterase (AChE), followed by odorant response gene-1 (ODR1) and neuropeptide G-protein coupled receptor (nGPCR) in Mi, suggesting the possible suppression of neurotransmission and chemosensing functions. Among the target proteins of Fol, AITC was the most effective protein in blocking chitin synthase (CS), followed by 2,3-dihydroxy benzoic acid decarboxylase (6m53) and trypsinase (1try), thus inferring these as the principal molecular targets of fungal growth. Taken together, the study establishes the potential of MEO as a novel biopesticide lead, which will be utilized further to manage the Mi-Fol disease complex.

New Insights on the Role of Allyl Isothiocyanate in Controlling the Root Knot Nematode Meloidogyne hapla

Biofumigation, although a well-known method, is still controversially debated as a management strategy for plant-parasitic nematodes (PPN). Its controlling effect is attributed to the production of isothiocyanates (ITCs) following the action of myrosinase on glucosinolates (GSLs). Different ITCs are formed from different GSLs, depending on the plant species. To better understand the potential of ITCs, eight cultivars from three Brassicaceae species were investigated as biofumigation crops to control the root knot nematode Meloidogyne hapla. Since results were inconsistent, the nematicidal effect of selected ITCs were further evaluated in vitro. Based on its nematicidal potential, allyl ITC (AITC) was specifically investigated under different soil:sand compositions. A significantly lower nematicidal activity was observed in soil compared to sand. AITC was also evaluated as an additive to the biofumigation in a greenhouse trial. Its supplementation to the biofumigation process with Brassica juncea cv. Terrafit controlled M. hapla, while no control was observed using Raphanus sativus cv. Defender. Thus, the success of biofumigation seems to be strongly dependent on the soil characteristics and the ITC produced during the biofumigation process. Therefore, the supplementation of AITC in combination with the right cover crop can improve the biofumigation process to control M. hapla.

Soil properties, presence of microorganisms, application dose, soil moisture and temperature influence the degradation rate of Allyl isothiocyanate in soil

Allyl isothiocyanate (AITC) is a soil fumigant derived from plants that can effectively control soil-borne diseases. Fully understanding the impact of various factors on its degradation can contribute to its effectiveness against pests and diseases. First, orthogonal design determined the extraction method of AITC in soil, that is using ethyl acetate as the extraction reagent, vortexing for 1 min as the extraction method and holding for 30 min as the method time. Then we studied the effects of soil texture and environmental factors on the rate and extent of AITC degradation in soil. The half-lives of nine origins soils varied from 12.2 to 71.8 h that were affected by the soil's electrical conductivity, available nitrogen, pH and organic matter content. Biotic degradation of AITC contributed significantly (68%-90%) of the total AITC degradation in six soil types. The degradation rate of AITC decreased as the initial dose of AITC increased. The degradation rate of AITC in Suihua soil generally increased with increasing temperature and soil moisture. The effect of temperature on AITC degradation was more pronounced when the soil was moist, which has practical implications for the control of soil pests and diseases. In agricultural soil, the soil's characteristics and environmental factors should be considered when determining the appropriate AITC dose suitable for soil borne disease while at the same time minimizing emissions and impact on the environment.

2-Phenylethyl Isothiocyanate Exerts Antifungal Activity against Alternaria alternata by Affecting Membrane Integrity and Mycotoxin Production

Black spot caused by Alternaria alternata is one of the important diseases of pear fruit during storage. Isothiocyanates are known as being strong antifungal compounds in vitro against different fungi. The aim of this study was to assess the antifungal effects of the volatile compound 2-phenylethyl isothiocyanate (2-PEITC) against A. alternata in vitro and in pear fruit, and to explore the underlying inhibitory mechanisms. The in vitro results showed that 2-PEITC significantly inhibited spore germination and mycelial growth of A. alternata-the inhibitory effects showed a dose-dependent pattern and the minimum inhibitory concentration (MIC) was 1.22 mM. The development of black spot rot on the pear fruit inoculated with A. alternata was also significantly decreased by 2-PEITC fumigation. At 1.22 mM concentration, the lesion diameter was only 39% of that in the control fruit at 7 days after inoculation. Further results of the leakage of electrolyte, increase of intracellular OD260, and propidium iodide (PI) staining proved that 2-PEITC broke cell membrane permeability of A. alternata. Moreover, 2-PEITC treatment significantly decreased alternariol (AOH), alternariolmonomethyl ether (AME), altenuene (ALT), and tentoxin (TEN) contents of A. alternata. Taken together, these data suggest that the mechanisms underlying the antifungal effect of 2-PEITC against A. alternata might be via reduction in toxin content and breakdown of cell membrane integrity.

Benzyl isothiocyanate fumigation inhibits growth, membrane integrity and mycotoxin production inAlternaria alternata

The antifungal activity of benzyl isothiocyanate (BITC) against pear pathotype-Alternaria alternata, the causal agent of pear black spot, and its possible mechanisms were studied. The results indicated that both the spore germination and mycelial growth of A. alternata were significantly inhibited by BITC in a dose-dependent manner. BITC concentrations at 1.25 mM completely suppressed mycelial growth of A. alternata and prevented ≥50% of black spot development in wounded pears inoculated with A. alternata. Microscopic analyses and propidium iodide (PI) staining showed that spore morphology in A. alternata treated with BITC at 0.625 mM was severely damaged. Relative electrical conductivity and lysis ability assays further showed that BITC treatment destroyed the integrity of the plasma membrane. Additionally, mycotoxin production was inhibited by 0.312 mM BITC, and the inhibitory rates of alternariol monomethyl ether (AME), alternariol (AOH), altenuene (ALT) and tentoxin (TEN) were 89.36%, 84.57%, 91.41% and 67.78%, respectively. The above results suggest that BITC exerts antifungal activity through membrane-targeted mechanisms.

The antifungal activity of benzyl isothiocyanate (BITC) against pear pathotype-Alternaria alternata, the causal agent of pear black spot, and its possible mechanisms were studied.

Dynamic biospeckle analysis, a new tool for the fast screening of plant nematicide selectivity

BACKGROUND

Plant feeding, free-living nematodes cause extensive damage to plant roots by direct feeding and, in the case of some trichodorid and longidorid species, through the transmission of viruses. Developing more environmentally friendly, target-specific nematicides is currently impeded by slow and laborious methods of toxicity testing. Here, we developed a bioactivity assay based on the dynamics of light 'speckle' generated by living cells and we demonstrate its application by assessing chemicals' toxicity to different nematode trophic groups.

RESULTS

Free-living nematode populations extracted from soil were exposed to methanol and phenyl isothiocyanate (PEITC). Biospeckle analysis revealed differing behavioural responses as a function of nematode feeding groups. Trichodorus nematodes were less sensitive than were bacterial feeding nematodes or non-trichodorid plant feeding nematodes. Following 24 h of exposure to PEITC, bioactivity significantly decreased for plant and bacterial feeders but not for Trichodorus nematodes. Decreases in movement for plant and bacterial feeders in the presence of PEITC also led to measurable changes to the morphology of biospeckle patterns.

CONCLUSIONS

Biospeckle analysis can be used to accelerate the screening of nematode bioactivity, thereby providing a fast way of testing the specificity of potential nematicidal compounds. With nematodes' distinctive movement and activity levels being visible in the biospeckle pattern, the technique has potential to screen the behavioural responses of diverse trophic nematode communities. The method discriminates both behavioural responses, morphological traits and activity levels and hence could be used to assess the specificity of nematicidal compounds.

Plant Immune Responses to Parasitic Nematodes

Plant-parasitic nematodes (PPNs), such as root-knot nematodes (RKNs) and cyst nematodes (CNs), are among the most devastating pests in agriculture. RKNs and CNs induce redifferentiation of root cells into feeding cells, which provide water and nutrients to these nematodes. Plants trigger immune responses to PPN infection by recognizing PPN invasion through several different but complementary systems. Plants recognize pathogen-associated molecular patterns (PAMPs) sderived from PPNs by cell surface-localized pattern recognition receptors (PRRs), leading to pattern-triggered immunity (PTI). Plants can also recognize tissue and cellular damage caused by invasion or migration of PPNs through PRR-based recognition of damage-associated molecular patterns (DAMPs). Resistant plants have the added ability to recognize PPN effectors via intracellular nucleotide-binding domain leucine-rich repeat (NLR)-type immune receptors, leading to NLR-triggered immunity. Some PRRs may also recognize apoplastic PPN effectors and induce PTI. Plant immune responses against PPNs include the secretion of anti-nematode enzymes, the production of anti-nematode compounds, cell wall reinforcement, production of reactive oxygen species and nitric oxide, and hypersensitive response-mediated cell death. In this review, we summarize the recognition mechanisms for PPN infection and what is known about PPN-induced immune responses in plants.

Plant Volatiles Reduce the Viability of the Root-Knot Nematode Meloidogyne incognita Either Directly or When Retained in Water

Volatile organic compounds (VOC) produced by green residues for the management of plant-parasitic nematodes are poorly studied for oilseed plants and some Brassica spp. To investigate the activity of VOC in vitro and as biofumigants, dry and aqueous macerates of broccoli (Brassica oleracea var. italica) shoots and sunflower (Helianthus annuus) seed were used against the root-knot nematode Meloidogyne incognita. VOC produced by sunflower seed caused higher mortality of M. incognita second-stage juveniles (J₂) than VOC produced by broccoli shoots but both plant species were equally effective in decreasing the infectivity and reproduction of this nematode. The number of galls and eggs produced by the nematode in tomato roots was reduced by 89 and 95%, respectively, on average, at the highest concentrations of broccoli and sunflower seed macerates tested as biofumigants. When nematodes were placed in water exposed to broccoli VOC, J₂ immobility increased and the number of galls and eggs produced by the nematode in tomato roots decreased 80 and 96%, respectively. Water exposed to sunflower seed VOC had no effect on the viability of the nematode. Gas chromatography was used to identify five and six chemical groups in broccoli and in sunflower seed macerates, respectively, but only alcohols, sulfurated VOC, and terpenes were detected in the water exposed to these plant macerates. Sulfurated VOC from the water exposed to broccoli macerates were found to be involved in its activity against M. incognita. The purified VOC dimethyl disulfide (DMDS) and 3-pentanol were tested directly against J₂ and showed a lethal concentration of 176 and 918 µg/ml (ppm), respectively, whereas dimethyl sulfide had no effect against M. incognita. Furthermore, DMDS and 3-pentanol retained in water killed J₂ and reduced gall formation and the number of eggs of M. incognita on tomato roots. Both these plant species produced toxic VOC to M. incognita, whereas only VOC retained in water exposed to broccoli had activity against M. incognita.

Functional Profiling and Crystal Structures of Isothiocyanate Hydrolases Found in Gut-Associated and Plant-Pathogenic Bacteria

Isothiocyanates (ITCs) are produced by cruciferous plants to protect them against herbivores and infection by microbes. These compounds are of particular interest due to their antimicrobial and anticarcinogenic properties. The breakdown of ITCs in nature is catalyzed by isothiocyanate hydrolases (ITCases), a novel family within the metallo-β-lactamase (MBL)-fold superfamily of proteins. saxA genes that code for ITCases are particularly widespread in insect- and plant-associated bacteria. Enzymatic characterization of seven phylogenetically related but distinct ITCases revealed similar activities on six selected ITCs, suggesting that phylogenetic diversity does not determine the substrate specificity of ITCases. X-ray crystallography studies of two ITCases sharing 42% amino acid sequence identity revealed a highly conserved tertiary structure. Notable features of ITCases include a hydrophobic active site with two Zn²⁺ ions coordinating water/hydroxide and a flexible cap that is implicated in substrate recognition and covers the active site. This report reveals the function and structure of the previously uncharacterized family of isothiocyanate hydrolases within the otherwise relatively well-studied superfamily of metallo-β-lactamases.IMPORTANCE This study explores a newly discovered protein in the β-lactamase superfamily, namely, SaxA, or isothiocyanate hydrolase. Isothiocyanates are defensive compounds found in many cabbage-related crop plants and are currently being investigated for their antimicrobial and anticarcinogenic properties. We show that isothiocyanate hydrolases are responsible for the breakdown of several of these plant defensive chemicals in vitro and suggest their potential for mitigating the beneficial effects of isothiocyanates in crop protection and cancer prevention.

Evaluation of allyl isothiocyanate as a soil fumigant against soil-borne diseases in commercial tomato (Lycopersicon esculentum Mill.) production in China

BACKGROUND

Root-knot nematodes (Meloidogyne spp.), soil-borne diseases and weeds seriously reduce the commercial yield of tomatoes grown under protected cultivation in China. Allyl isothiocyanate (AITC), a natural product obtained from damaged Brassica tissues, was evaluated as a potential replacement for the fumigant methyl bromide (MB) for use in the greenhouse production of tomatoes in China.

RESULTS

The dose-response assay indicates that AITC has high biological activity against major bacterial and fungal pathogens (EC50 of 0.225-4.199 mg L-1 ). The bioassay results indicate that AITC has good efficacy against root-knot nematodes (LC50 of 18.046 mg kg-1 ), and moderate efficacy against fungal pathogens (LC50 of 27.999-29.497 mg kg-1 ) and weeds (LC50 of 17.300-47.660 mg kg-1 ). The potting test indicates that AITC significantly improved plant vigor. Field trials indicate that AITC showed good efficacy against Meloidogyne spp. and Fusarium spp. (both ∼ 80%) as well as Phytophthora spp. and Pythium spp. (both ∼ 70%), and improved plant vigor and marketable yield.

CONCLUSION

AITC used as a soil fumigant (30-50 g m-2 ) effectively controlled major bacterial and fungal pathogens, root-knot nematode, weeds and increased plant vigor, yield and farmers' income in tomato cultivated under protected agriculture in China. © 2018 Society of Chemical Industry.

Benzyl isothiocyanate affects development, hatching and reproduction of the soybean cyst nematode Heterodera glycines

Benzyl isothiocyanate (BITC), prepared in 1% methanol and applied at micro-molar doses, decreased Heterodera glycines infective second-stage juvenile (J2) movement, hatching and reproduction on soybean, Glycine max. Direct exposure of J2 to 30 μM BITC caused an immediate decrease (17%) in J2 movement relative to 1% methanol controls, and within 3 h exposure eliminated >99% of movement. Continuous exposure of H. glycines eggs to 30 μM or 60 μM BITC significantly decreased percentage hatch of J2 measured at 7 days (30 μM, 15.8 ± 2.4%; 60 μM, 7.9 ± 2.2%) relative to controls (44.9 ± 4.1%). Control percentage hatch increased between days 7 and 14 (87.5 ± 2.3%), whereas there was no significant increase in hatch after Day 7 in either treatment group. The effect of BITC on hatch was rapid and persistent. Following 4 h exposure of eggs to either 30 μM or 60 μM BITC and transfer to water, percentage hatch at Day 14 was 51.3 ± 6.3% and 15.6 ± 1.4%, respectively. Each value was significantly less than the control percentage hatch (96.5 ± 0.2%). The same treatment method also resulted in decreased reproduction. The mean number of cysts per plant harvested 5 weeks after inoculation with control eggs (173.0 ± 12.1) was significantly greater than the numbers from plants inoculated with either 30 μM (78.9 ± 8.2) or 60 μM (38.3 ± 4.5) BITC treated eggs. Reduction of hatch and reproduction were strongly correlated, with for both 30 μM or 60 μM BITC treatments. The effects of BITC were primarily on the early embryo. The percent of all embryos in the multicellular stage at Day 14 in control eggs was 4.9 ± 0.7%, but increased to 35.1 ± 4.3% (30 μM) and 56.3 ± 4.5% (60 μM) in BITC treated eggs. BITC has multiple effects on H. glycines, affecting both infective juvenile movement and embryonic development, and decreasing reproduction.

Targeting internal processes of plant-parasitic nematodes in the pursuit of novel agents for their control

The success of plant-parasitic nematodes as competitors with humans for crops is evidenced by the parasites’ significant and continuous economic drain on global agriculture. Scientific efforts dedicated to the control of plant-parasitic nematodes employ strategies from the environmental to molecular levels. Understanding the interaction of the nematode with its environment, and the molecules involved, offers great promise for novel control agent development. Perhaps more significantly, such knowledge facilitates the generation of ever more detailed and sophisticated information on nematode biology and new molecular targets. Among the most economically important groups of plant-parasitic nematodes are those comprising the cyst-forming species and the root-knot nematodes. Presented here is a brief overview of research into the biology of these parasites relative to their life cycles. Recent advances in elucidating the molecular biology and biochemistry of nematode-plant interactions during the internal parasitic stages of the life cycle have been driven by advances in genomics and transcriptomics. The remarkable discoveries regarding parasitism, and the application of genetic resources in these findings, provide a template for advanced investigation of external, survival stages biology. While survival biology research lags somewhat behind that of parasitism with regard to the molecular genetics of signalling and response, its extensive catalogue promises explosive rates of discovery as progress in genomics and transcriptomics allows a molecular genetic examination of embryogenesis, dormancy and hatching. Our group is interested in behaviour, development and hatching of cyst and root-knot nematodes, and the effects of the environment on the mechanisms of these activities. Phytochemical and temperature effects are discussed, and evidence is presented that the cyst may provide useful molecules for exploring nematode physiology.

Crosstalk between above- and belowground herbivores is mediated by minute metabolic responses of the host Arabidopsis thaliana

Plants are frequently under attack by multiple herbivores and can be infested at their shoots as well as their roots. As a consequence, plant metabolites are readily induced, mediated by phytohormones such as salicylic acid and jasmonic acid. Thereby, cross-talk between signal transduction pathways may occur if different herbivores attack the plant simultaneously. In turn, modifications in the plant metabolic pattern can affect herbivores infesting local and systemic tissue. Here, an integrative approach combining metabolomics and performance experiments was used to study the induction of plant metabolites in Arabidopsis thaliana by the specialist aphid Brevicoryne brassicae feeding on shoots and the generalist nematode Heterodera schachtii infesting root tissue. In contrast to most other studies, low infestation rates typical for the decisive early stages of infestation were used. Moreover, the consequences of induction responses on plant-mediated indirect interactions between these herbivores were investigated. In aphid-treated plants, several metabolites including glucosinolates, important defence compounds of Brassicaceae, were reduced in the shoot, but only minute changes took part in the systemic root tissue. Primary metabolites as well as phytohormones were not altered 3 days post infestation. In contrast, nematodes did not evoke significant metabolic alterations locally or systemically. In accordance, nematode presence did not affect aphid population growth, whereas aphids mediated a considerably reduced nematode infestation. These results demonstrate that plants respond in a very fine-tuned way to different challenges. Although they show only minute systemic responses to low herbivore stress, these changes can have pronounced effects on plant-mediated interactions between herbivores.

Activity of meadowfoam (Limnanthes alba) seed meal glucolimnanthin degradation products against soilborne pathogens

Meadowfoam (Limnanthes alba L.) is a herbaceous winter-spring annual grown as a commercial oilseed crop. The meal remaining after oil extraction from the seed contains up to 4% of the glucosinolate glucolimnanthin. Degradation of glucolimnanthin yields toxic breakdown products, and therefore the meal may have potential in the management of soilborne pathogens. To maximize the pest-suppressive potential of meadowfoam seed meal, it would be beneficial to know the toxicity of individual glucolimnanthin degradation products against specific soilborne pathogens. Meloidogyne hapla second-stage juveniles (J2) and Pythium irregulare and Verticillium dahliae mycelial cultures were exposed to glucolimnanthin as well as its degradation products. Glucolimnanthin and its degradation product, 2-(3-methoxyphenyl)acetamide, were not toxic to any of the soilborne pathogens at concentrations up to 1.0 mg/mL. Two other degradation products, 2-(3-methoxymethyl)ethanethioamide and 3-methoxyphenylacetonitrile, were toxic to M. hapla and P. irregulare but not V. dahliae. The predominant enzyme degradation product, 3-methoxybenzyl isothiocyanate, was the most toxic compound against all of the soilborne pathogens, with M. hapla being the most sensitive with EC(50) values (0.0025 ± 0.0001 to 0.0027 ± 0.0001 mg/mL) 20-40 times lower than estimated EC(50) mortality values generated for P. irregulare and V. dahliae (0.05 and 0.1 mg/mL, respectively). The potential exists to manipulate meadowfoam seed meal to promote the production of specific degradation products. The conversion of glucolimnanthin into its corresponding isothiocyanate should optimize the biopesticidal properties of meadowfoam seed meal against M. hapla, P. irregulare, and V. dahliae.

Biofumigation for control of pale potato cyst nematodes: activity of brassica leaf extracts and green manures on Globodera pallida in vitro and in soil

The effects of brassica green manures on Globodera pallida were assessed in vitro and in soil microcosms. Twelve of 22 brassica accessions significantly inhibited the motility of G. pallida infective juveniles in vitro. Green manures of selected brassicas were then incorporated into soil containing encysted eggs of G. pallida. Their effect on egg viability was estimated by quantifying nematode actin 1 mRNA by RT-qPCR. The leaf glucosinolate profiles of the plants were determined by high-performance liquid chromatography. Three Brassica juncea lines (Nemfix, Fumus, and ISCI99) containing high concentrations of 2-propenyl glucosinolate were the most effective, causing over 95% mortality of encysted eggs of G. pallida in polyethylene-covered soil. The toxic effects of green manures were greater in polyethylene-covered than in open soil. Toxicity in soil correlated with the concentration of isothiocyanate-producing glucosinolate but not total glucosinolate in green manures.

Antimutagenic potential of glucosinolate-rich seed extracts of broccoli (Brassica oleracea L var italica Plenck)

In the current study, isolation of glucosinolate degradation products was done in 4 different incubation solutions with different pHs based on the fact that distinct hydrolytic products are formed at different pHs. All the extracts were tested against direct-acting mutagens (4 nitro-o-phenylenediamine [NPD]), sodium azide, and indirect-acting mutagen (2-aminofluorene [2AF]). It was observed that extracts inhibited mutagenesis induced by the S9-dependent mutagen (2AF) more significantly than direct-acting mutagens. Two different modes of experimentation (pre-incubation and co-incubation) were used, and it was observed that the extracts showed better results in the pre-incubation mode of experimentation. Out of the 4 extracts tested, 0.1 mol/L of HCl extract was found to be the most effective in inhibiting mutagenesis with both TA 98 and TA 100 strains of Salmonella typhimurium. All other extracts also showed pronounced antimutagenic potential. The results of this study indicate the presence of potent antigenotoxic factors in broccoli, which are being explored further for their mechanism of action.

The toxic effects of benzyl glucosinolate and its hydrolysis product, the biofumigant benzyl isothiocyanate, to Folsomia fimetaria

Natural isothiocyanates (ITCs) are toxic to a range of pathogenic soil-living species, including nematodes and fungi, and can thus be used as natural fumigants called biofumigants. Natural isothiocyanates are hydrolysis products of glucosinolates (GSLs) released from plants after cell rupture. The study investigated the toxic effects of benzyl-GSL and its hydrolysis product benzyl-ITC on the springtail Folsomia fimetaria, a beneficial nontarget soil-dwelling micro-arthropod. The soil used was a sandy agricultural soil. Half-lives for benzyl-ITC in the soil depended on the initial soil concentration, ranging from 0.2 h for 67 nmol/g to 13.2 h for 3,351 nmol/g. For benzyl-ITC, the concentration resulting in 50% lethality (LC50) value for F. fimetaria adult mortality was 110 nmol/g (16.4 mg/kg) and the concentration resulting in 50% effect (EC50) value for juvenile production was 65 nmol/g (9.7 mg/kg). Benzyl-GSL proved to be less toxic and consequently an LC50 value for mortality could not be estimated for springtails exposed to benzyl-GSL. For reproduction, an EC50 value was estimated to approximately 690 nmol/g. The study indicates that natural soil concentrations of ITCs may be toxic to beneficial nontarget soil-dwelling arthropods such as springtails.

Managing nematodes without methyl bromide

Methyl bromide is an effective pre-plant soil fumigant used to control nematodes in many high-input, high-value crops in the United States, including vegetables, nursery plants, ornamentals, tree fruits, strawberries, and grapes. Because methyl bromide has provided a reliable return on investment for nematode control, many of these commodities have standardized their production practices based on the use of this chemical and will be negatively impacted if effective and economical alternatives are not identified. Alternative control measures based on other chemicals, genetic resistance, and cultural practices require a greater knowledge of nematode biology to achieve satisfactory results. Here, we provide an overview of nematode management practices that we believe will be relied upon heavily in U.S. high-value crop production systems in a world without methyl bromide. Included are case studies of U.S. high-value crop production systems to demonstrate how nematode management practices other than methyl bromide may be incorporated.

Metabolomic differentiation of Brassica rapa following herbivory by different insect instars using two-dimensional nuclear magnetic resonance spectroscopy

The metabolic alterations of Brassica rapa (L.) leaves attacked by larvae of the specialist Plutella xylostella L. (Lepidoptera: Yponomeutidae) and the generalist Spodoptera exigua Hubner (Lepidoptera: Noctuidae) were investigated with nuclear magnetic resonance (NMR) spectroscopy, followed by a multivariate data analysis. The principal component analysis (PCA) of (1)H NMR spectra showed that metabolic changes in B. rapa leaves induced by the 2nd and the 4th instars were different from each other. However, the congestion of the one-dimensional (1)H NMR spectrum made it difficult to identify discriminating metabolites. To overcome the spectral complexity, several two-dimensional NMR techniques were applied. Of those evaluated, J-resolved spectroscopy, which affords an additional coupling constant, provided a wide range of structure information on differentiating the metabolites. Based on the J-resolved spectra combined with PCA, the major signals contributing to the discrimination were alanine, threonine, glucose, sucrose, feruloyl malate, sinapoyl malate, and gluconapin.

Uptake and turn-over of glucosinolates sequestered in the sawfly Athalia rosae

Larvae of the sawfly Athalia rosae sequester glucosinolates from their various host plants of the Brassicaceae into their hemolymph for defensive purposes. We found that the glucosinolate concentration in the insect varies in a fluctuating manner during larval development. Analyses of larvae which had been offered diets with different glucosinolate profiles showed that there is an equilibrium between a rapid uptake of glucosinolates into the hemolymph and a continuous turn-over. Injection of glucotropaeolin into the hemolymph and ingestion of the same amount resulted in similar levels of intact glucosinolates recovered from larvae after different periods of time. This indicates that hemolymph glucosinolates are the principal source for glucosinolate degradation. Feeding experiments with [14C]-labeled glucotropaeolin revealed that the majority of the ingested glucosinolate is excreted as one or more unidentified metabolite(s) within 14 h. We found no indication for the presence of an insect myrosinase, or sulfatase in A. rosae, which have been shown to be involved in glucosinolate metabolism in other specialists feeding on Brassicaceae. Furthermore, the metabolism of sinalbin in A. rosae seems to result in different products than its metabolism in the caterpillar Pieris rapae. Obviously, A. rosae has yet another way of coping with the glucosinolates.