Isothiocyanates Produced by Brassicaceae Species as Inhibitors of Fusarium oxysporum

Select Cover Crop Residue and Soil Microbiomes Contribute to Suppression of Fusarium Root and Crown Rot in Barley and Soybean

Fusarium root and crown rot (FRCR) negatively impact several economically important plant species. Cover crops host different soil and residue microbiomes, thereby potentially influencing pathogen load and disease severity. The carryover effect of cover crops on FRCR in barley and soybean was investigated. Field trials were conducted in Prince Edward Island, Canada. Two cover crops from each plant group, including forbs, brassicas, legumes, and grasses, were grown in a randomized complete block design with barley and soybean planted in split plots the following year. Barley and soybean roots were assessed for FRCR through visual disease rating and Fusarium spp. were isolated from diseased tissue. Fungal and bacterial communities in cover crop residues were quantified using amplicon sequencing. The disease-suppressive effects of soil were tested in greenhouse studies. The results indicated that sorghum-sudangrass-associated microbiomes suppress Fusarium spp., leading to reduced FRCR in both barley and soybean. The oilseed radish microbiome had the opposite effect, consequently increasing FRCR incidence in barley and soybean. The results from this study indicate that cover crop residue and the associated soil microbiome influence the incidence and severity of FRCR in subsequent crops. This information can be used to determine cover cropping strategies in barley and soybean production systems.

Ethyl Isothiocyanate as a Novel Antifungal Agent Against Candida albicans

In the recent years, occurrence of candidiasis has increased drastically which leads to significant mortality and morbidity mainly in immune compromised patients. Glucosinolate (GLS) derivatives are reported to have antifungal activities. Ethyl isothiocyanate (EITC) and its antifungal activity and mechanism of action is still unclear against Candida albicans. The present work was designed to get a mechanistic insight in to the anti-Candida efficacy of EITC through in vitro and in vivo studies. EITC inhibited C. albicans planktonic growth at 0.5 mg/ml and virulence factors like yeast to hyphal form morphogenesis (0.0312 mg/ml), adhesion to polystyrene surface (0.0312 mg/ml) and biofilm formation (developing biofilm at 2 mg/ml and mature biofilm at 0.5 mg/ml) effectively. EITC blocked ergosterol biosynthesis and arrested C. albicans cells at S-phase. EITC caused ROS-dependent cellular death and nuclear or DNA fragmentation. EITC at 0.0312 mg/ml concentration regulated the expression of genes involved in the signal transduction pathway and inhibited yeast to hyphal form morphogenesis by upregulating TUP1, MIG1, and NRG1 by 3.10, 5.84 and 2.64-fold, respectively and downregulating PDE2 and CEK1 genes by 15.38 and 2.10-fold, respectively. EITC has showed haemolytic activity at 0.5 mg/ml concentration. In vivo study in silk worm model showed that EITC has toxicity to C. albicans at 0.5 mg/ml concentration. Thus, from present study we conclude that EITC has antifungal activity and to reduce its MIC and toxicity, combination study with other antifungal drugs need to be done. EITC and its combinations might be used as alternative therapeutics for the prevention and treatment of C. albicans infections.

In vitro inhibition of Sclerotinia sclerotiorum mycelial growth and reduction of sclerotial viability by the volatile bioactive compounds of Brassicaceae crops

AIMS

Sclerotinia sclerotiorum is an important pathogen of a wide range of crops, with current control mostly relying on the use of fungicides. This study assessed the effect of biofumigation on in vitro inhibition of mycelial growth and reduction of sclerotial viability of S. sclerotiorum as an attempt to seek an alternative management strategy.

METHODS AND RESULTS

The effect of different biofumigant crop types to inhibit mycelial growth of ten S. sclerotiorum isolates was investigated, with Brassica juncea 'Caliente 199' being the most effective biofumigant crop. The efficacy of 'Caliente 199' to inhibit mycelial growth and reduce sclerotial viability was influenced by different crop factors. Plant tissue of 'Caliente 199' harvested at 50% or 100% flowering and adjusted to 80% (w/w) moisture resulted in greater mycelial inhibition and a reduction in the sclerotial viability compared with the vegetative tissue with the same plant moisture. Mycelial inhibition and reduction of sclerotial viability were affected by tissue quantity. Whole plant tissue and shoots only resulted in a similar inhibition of mycelial growth, but whole plant tissue resulted in a greater reduction of sclerotial viability. The S. sclerotiorum isolates differed in sensitivity to the volatile bioactive compounds released by the biofumigant plant tissue.

CONCLUSIONS

The volatile bioactive compounds released by 'Caliente 199' resulted in effective mycelial inhibition but did not kill sclerotia completely.

Molecular interactions between the soilborne pathogenic fungus Macrophomina phaseolina and its host plants

Mentioned for the first time in an article 1971, the occurrence of the term "Macrophomina phaseolina" has experienced a steep increase in the scientific literature over the past 15 years. Concurrently, incidences of M. phaseolina-caused crop diseases have been getting more frequent. The high levels of diversity and plasticity observed for M. phasolina genomes along with a rich equipment of plant cell wall degrading enzymes, secondary metabolites and putative virulence effectors as well as the unusual longevity of microsclerotia, their asexual reproduction structures, make this pathogen very difficult to control and crop protection against it very challenging. During the past years several studies have emerged reporting on host defense measures against M. phaseolina, as well as mechanisms of pathogenicity employed by this fungal pathogen. While most of these studies have been performed in crop systems, such as soybean or sesame, recently interactions of M. phaseolina with the model plant Arabidopsis thaliana have been described. Collectively, results from various studies are hinting at a complex infection cycle of M. phaseolina, which exhibits an early biotrophic phase and switches to necrotrophy at later time points during the infection process. Consequently, responses of the hosts are complex and seem coordinated by multiple defense-associated phytohormones. However, at this point no robust and strong host defense mechanism against M. phaseolina has been described.

Isothiocyanates as potential antifungal agents: a mini-review

Cruciferous vegetables and mustard oil are rich in the glucosinolate group of molecules. Isothiocyanates are an important group of glucosinolate derivatives. These derivatives have various bioactive properties, including antioxidant, antibacterial, anticarcinogenic, antifungal, antiparasitic, herbicidal and antimutagenic activity. Previous studies indicate that regular intake of such vegetables may considerably reduce the incidence of various types of cancer. These studies have inspired studies where the bioactive agents of these plants have been isolated and explored for their therapeutic applications. The use of these bioactive compounds as antifungals could be a new therapeutic approach against human pathogenic fungi. Isothiocyanates have been studied for their antifungal activity and have the potential to be used for antifungal therapy.

Volatile Oils Discrepancy between Male and Female Ochradenus arabicus and Their Allelopathic Activity on Dactyloctenium aegyptium

Volatile oils (VOs) composition of plants is affected by several exogenous and endogenous factors. Male and female plants of the dioecious species exhibit variation in the bioactive constituents' allocation. The chemical variation in the VOs between male and female plants is not well studied. In the present study, the chemical characterization of the VOs extracted from aerial parts of male and female ecospecies of Ochradenus arabicus was documented. Additionally, the extracted VOs were tested for their allelopathic activity against the weed Dactyloctenium aegyptium. Via GC-MS analysis, a total of 53 compounds were identified in both male and female plants. Among them, 49 compounds were identified from male plants, and 47 compounds were characterized in female plants. Isothiocyanates (47.50% in male and 84.32% in female) and terpenes (48.05% in male and 13.22% in female) were the main components of VOs, in addition to traces of carotenoid-derived compounds and hydrocarbons. The major identified compounds of male and female plants are m-tolyl isothiocyanate, benzyl isothiocyanate, butyl isothiocyanate, isobutyl isothiocyanate, carvone, and α-bisabolol, where they showed variation in the concentration between male and female plants. The O. arabicus VOs of the male plants attained IC₅₀ values of 51.1, 58.1, and 41.9 μL L^-1 for the seed germination, seedling shoot growth, and seedling root growth of the weed (D. aegyptium), respectively, while the females showed IC₅₀ values of 56.7, 63.9, and 40.7 μL L^-1, respectively. The present data revealed that VOs composition and bioactivity varied significantly with respect to the plant gender, either qualitatively or quantitatively.

Antifungal Effect of Brassica Tissues on the Mycotoxigenic Cereal Pathogen Fusarium graminearum

Fusarium graminearum is a globally important cereal pathogen, causing head blight in wheat, resulting in yield losses and mycotoxin contamination. Currently, triazole fungicides are used to suppress Fusarium graminearum, however, the declining effectiveness of triazoles and concerns over the safety of pesticides have led to the pursuit of safe alternative crop protection strategies such as biofumigation. In the present study, species belonging to Brassicaceae (Brassica juncea, Raphanus sativus, Eruca sativa) were assessed for their biofumigation potential against F. graminearum and the glucosinolate profile of the brassicas was determined. In Petri dishes, mycelial plugs of Fusarium graminearum were exposed to frozen/defrosted leaf discs of brassicas collected at early-leaf, stem-extension, and early-bud stages. Additionally, F. graminearum inoculum was incubated in soil amended with chopped tissues of brassicas in a closed jar experiment. Glucosinolate analysis of the leaf tissue of brassicas revealed that the total glucosinolate concentration of B. juncea ‘Brons’ increased with advancing growth stage (24.5–51.9 µmol g⁻¹). Brassica juncea leaf discs were effective against mycelial growth, while the sinigrin content in the leaf tissue corresponded to the level of suppression. At the stem-extension and early-bud stages, B. juncea ‘Brons’ showed 87–90% suppression with four leaf discs, and 100% suppression with eight leaf discs. Brassica juncea ‘Caliente Rojo’ leaf discs collected at the stem-extension stage showed 94% inhibition with eight discs. In the closed jar experiment, each brassica species significantly suppressed F. graminearum inoculum by 41–55%. The findings suggest that the brassica species investigated in the present study could be effective in reducing the inoculum of F. graminearum in soil prior to cereal production.

In vitro compatibility of Brassicaceae extracts with nematophagous fungi and their effects against Nacobbus celatus

Nacobbus celatus sp. n. is one of the main root-knot nematodes in the field destined for horticultural production of the central region of Argentine due to its ability to infect several host plants. The lack of new and safe active ingredients against this nematode has restricted control alternatives for growers. Egg-parasitic fungi and biofumigation with brassicaceae have been considered as potential candidates for the development of bionematicides. Nematicidal effects of Brassica oleracea var. italica (broccoli) and Brassica oleracea var. capitata (cabbage) aqueous extracts (AEs) against second-stage juveniles (J2) of N. celatus were evaluated in vitro. Fisher LSD tests evidenced significant nematicidal (α = 0.05) effects of the two AEs tested, with LD₁₀₀ of 250 and 500 μL mL^-1 for broccoli and cabbage, respectively. Compatibility assays between AEs and five nematophagous fungi were performed on soil extract medium conditioned at 0.99 water activity and incubated at 30, 25 and 20 °C. Purpureocillium lilacinum SR14 was the fungal strain that showed compatibility at levels of spore viability, growth rate and conidia productions at LD₅₀ (125 μL mL^-1) and LD₂₅ (60 μL mL^-1) of broccoli aqueous extract (BAE) and enhanced the nematophagous effect. Moreover, phytotoxic studies revealed that 125 μL mL^-1 of BAE applied at the transplantation time could be safely used without affecting tomato culture. In conclusion, the integrated application of BAE with P. lilacinum SR14, which combines two action mechanisms, represents a promising integrated strategy to management phytoparasitic nematodes.

Responses of Fungi Maggot (Bradysia impatiens Johannsen) to Allyl Isothiocyanate and High CO2

Botanical pesticide is highly recommended for integrated pest management (IPM), due to its merits such as environmental friendliness, safe to non-target organisms, operators, animals, and food consumers. The experiment was conducted to determine the lethal and sub-lethal effects of allyl isothiocyanate (AITC) on eggs, third instar larvae, pupae, and females and males of Bradysia impatiens Johannsen (B. impatiens). Different concentrations of AITC under ambient CO₂ by the conical flask sealed fumigation method were used for the experiment. The results showed that there was a significant linear relationship between different concentrations of AITC and the toxicity regression equation of B. impatiens. The sub-lethal concentrations of AITC had significant effects on the larval stage, pupal stage, pupation rate, pupal weight, adult emergence rate, and oviposition. The pupation rate, pupal weight, and adult emergency rate were significantly (p < 0.05) affected by AITC fumigation. The pupation rate was the lowest after fumigation treatment of AITC at LC₅₀ (36.67%), followed by LC₂₅ (41.94%), compared with the CK (81.39%). Female longevity was significantly (p < 0.05) shortened by fumigation at LC₂₅ (1.75 d) and LC₅₀ (1.64 d), compared with that of CK (2.94 d). Male longevity was shorter at LC₂₅ (1.56 d) than at LC₅₀ (1.25 d) and had no significant difference between these two treatments. The fumigation efficiency of AITC was significantly increased under high CO₂ condition. Furthermore, detoxification enzyme activities and antioxidant enzyme activities were accumulated under high CO₂ condition. The fumigation method in the application of AITC can be useful in areas where B. impatiens is a major concern.

The Role of the GSTF11 Gene in Resistance to Powdery Mildew Infection and Cold Stress

Oilseed rape (Brassica napus) is an economically important crop. In a temperate climate, powdery mildew Erysiphe crucifertaum can drastically reduce its yield. Nevertheless, cultivars resistant to this fungal disease have not yet been selected. Glutathione S-transferase GSTF11 is involved in glucosinolate (GSL) biosynthesis and response to stress, including fungal deceases. However, the impact of exogenous GSTF11 gene expression on resistance to powdery mildew has not yet been confirmed and requires further investigation. Transgenic B. napus was generated for this purpose. It demonstrated increased GST activity and a higher GSH:GSSG ratio under normal conditions. Powdery mildew Erysiphe crucifertaum caused 50% mortality in wild type (WT) plants. In most of transgenic plants, mycelium growth was inhibited. The infection contributed to higher GSTF11 expression and increased levels of glutathione (GSH) and oxidized glutathione (GSSG) in both transgenic and WT plants. In contrast, GSTF11 mRNA content, GST activity and GSSG level were lower only in WT plants. In transgenic plants, increased resistance to powdery mildew correlated with a lower GSH:GSSG ratio, indicating a higher content of neutralized toxic molecules. GSTF11 expression was also affected by cold stress, but not drought. At -1 °C, the expression level increased only in transgenic plants. Therefore, GSTF11 appears to be nonspecific and is able to protect plants under several types of stress. This gene could be used as a target in the production of stress tolerant cultivars.

Effects of Glucosinolate-Derived Isothiocyanates on Fungi: A Comprehensive Review on Direct Effects, Mechanisms, Structure-Activity Relationship Data and Possible Agricultural Applications

Plants heavily rely on chemical defense systems against a variety of stressors. The glucosinolates in the Brassicaceae and some allies are the core molecules of one of the most researched such pathways. These natural products are enzymatically converted into isothiocyanates (ITCs) and occasionally other defensive volatile organic constituents (VOCs) upon fungal challenge or tissue disruption to protect the host against the stressor. The current review provides a comprehensive insight on the effects of the isothiocyanates on fungi, including, but not limited to mycorrhizal fungi and pathogens of Brassicaceae. In the review, our current knowledge on the following topics are summarized: direct antifungal activity and the proposed mechanisms of antifungal action, QSAR (quantitative structure-activity relationships), synergistic activity of ITCs with other agents, effects of ITCs on soil microbial composition and allelopathic activity. A detailed insight into the possible applications is also provided: the literature of biofumigation studies, inhibition of post-harvest pathogenesis and protection of various products including grains and fruits is also reviewed herein.

Uncovering the biofumigant capacity of allyl isothiocyanate from several Brassicaceae crops against Fusarium pathogens in maize

BACKGROUND

Driven by environmental concerns, chemical fumigants are no longer allowed in many countries. Therefore, other strategies for reducing fungal inoculum in soils and on crop debris are being explored. In the present study, several Brassicaceae crops were screened for their potential to control Fusarium gramineaum and Fusarium poae mycelial growth in an in vitro inverted Petri dish experiment. Volatile production was measured using gas chromatography-mass spectrometry headspace analysis. A selection of cultivars from each crop species was further investigated using a pot experiment with maize.

RESULTS

Ethiopian mustard (Brassica carinata) and brown mustard (Brassica juncea) released volatile allyl isothiocyanate (AITC) and a higher concentration of AITC was correlated with a better fungal growth reduction in the in vitro screening. Brown mustard cultivar Etamine completely inhibited growth of both Fusarium spp. Pure AITC in a solution with methanol resulted in a sigmoid dose-response curve for both Fusarium spp. tested. Fusarium poae appeared to be more tolerant to AITC than F. graminearum. A pot experiment revealed that the incorporation of brown mustard plant material could alleviate the clear negative effect of F. graminearum infection on maize growth.

CONCLUSION

The present study demonstrated the correlation between the fungistatic effect of biofumigation crops on Fusarium spp. and their production of volatile AITC in vitro, without the addition of exogenous enzymes, and confirmed the biofumigation potential of brown mustard in a pot experiment with maize. These results may help farmers when selecting a green manure crop suitable for biofumigation. © 2020 Society of Chemical Industry.

Plant surface metabolites as potent antifungal agents

Triunsaturated fatty acids are substrates for the synthesis of the defense hormone jasmonate which plays roles in resistance to numerous fungal pathogens. However, relatively little is known about other potential roles of di-unsaturated and triunsaturated fatty acids in resistance to fungal pathogens - in particular those that can attack plants at the seedling stage. We examined the roles of polyunsaturated fatty acids (PUFAs) in Arabidopsis thaliana during attack by the necrotrophic pathogen, Botrytis cinerea. We found that PUFA-deficient Arabidopsis mutants (fad2-1, fad2-3 and fad3-2 fad7-2 fad8 [fad trip]) displayed an unexpectedly strong resistance to B. cinerea at the cotyledon stage. Preliminary analyses revealed no changes in the expression of defense genes, however cuticle permeability defects were detected in both fad2-1 and fad trip mutants. Analysis of B. cinerea development on the surface of cotyledons revealed arrested hyphal growth on fad2-3 and fad trip mutants and 28% reduction in fungal adhesion on fad2-3 cotyledons. Surface metabolite analysis from the cotyledons of PUFA mutants led to the identification of 7-methylsulfonylheptyl glucosinolate (7MSOHG), which over-accumulated on the plant surface. We linked the appearance of 7MSOHG to defects in cuticle composition and permeability of mutants and show that its appearance correlates with resistance to B. cinerea.

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.

Use of Botanicals to Suppress Different Stages of the Life Cycle of Fusarium graminearum

Fusarium head blight (FHB) is one of the most important cereal diseases worldwide, causing yield losses and contamination of harvested products with mycotoxins. Fusarium graminearum is one of the most common FHB-causing species in wheat and barley cropping systems. We assessed the ability of different botanical extracts to suppress essential stages of the fungal life cycle using three strains of F. graminearum (FG0410, FG2113, and FG1145). The botanicals included aqueous extracts from white mustard (Sinapis alba) seed flour (Pure Yellow Mustard [PYM] and Tillecur [Ti]) as well as milled Chinese galls (CG). At 2% concentration (wt/vol), PYM and Ti completely inhibited growth of mycelium of all F. graminearum strains whereas, at 1%, CG reduced the growth by 65 to 83%, depending on the strain. While PYM and Ti reduced the germination of both conidia and ascospores at 2% (wt/vol), CG was only effective in reducing conidia germination. Perithecia formation of FG0410 but not FG2113 was suppressed by all botanicals. Moreover, application of botanicals on mature perithecia led to a two- to fourfold reduction in discharge of ascospores. Using liquid chromatography (LC) with diode array detection, we quantified the principal glucosinolate component sinalbin of PYM and Ti. LC time-of-flight mass spectrometry was used to demonstrate that the bioactive matrix of CG contains different gallotannins as well as gallic and tannic acids. Possible antifungal mechanisms of the botanical matrices are discussed. The results of this study are promising and suggest that PYM, Ti, and CG should be explored further for efficacy at managing FHB.[Formula: see text] Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Transcriptomic Analysis of Vibrio parahaemolyticus Reveals Different Virulence Gene Expression in Response to Benzyl Isothiocyanate

Vibrio parahaemolyticus isolated from seafood is a pathogenic microorganism that leads to several acute diseases that are harmful to our health and is frequently transmitted by food. Therefore, there is an urgent need for the control and suppression of this pathogen. In this paper, transcriptional analysis was used to determine the effect of treatment with benzyl isothiocyanate (BITC) extracted from cruciferous vegetables on V. parahaemolyticus and to elucidate the molecular mechanisms underlying the response to BITC. Treatment with BITC resulted in 332 differentially expressed genes, among which 137 genes were downregulated, while 195 genes were upregulated. Moreover, six differentially expressed genes (DEGs) in RNA sequencing studies were further verified by quantitative real-time polymerase chain reaction (qRT-PCR). Genes found to regulate virulence encoded an l-threonine 3-dehydrogenase, a GGDEF family protein, the outer membrane protein OmpV, a flagellum-specific adenosine triphosphate synthase, TolQ protein and VirK protein. Hence, the results allow us to speculate that BITC may be an effective control strategy for inhibiting microorganisms growing in foods.

Glucosinolates: Molecular structure, breakdown, genetic, bioavailability, properties and healthy and adverse effects

Glucosinolates are a large group of plant secondary metabolites with nutritional effects and biologically active compounds. Glucosinolates are mainly found in cruciferous plants such as Brassicaceae family, including common edible plants such as broccoli (Brassica oleracea var. italica), cabbage (B. oleracea var. capitata f. alba), cauliflower (B. oleracea var. botrytis), rapeseed (Brassica napus), mustard (Brassica nigra), and horseradish (Armoracia rusticana). If cruciferous plants are consumed without processing, myrosinase enzyme will hydrolyze the glucosinolates to various metabolites, such as isothiocyanates, nitriles, oxazolidine-2-thiones, and indole-3-carbinols. On the other hand, when cruciferous are cooked before consumption, myrosinase is inactivated and glucosinolates could be partially absorbed in their intact form through the gastrointestinal mucosa. This review paper summarizes the glucosinolate molecular breakdown, their genetic aspects from biosynthesis to precursors, their bioavailability (assimilation, absorption, and elimination of these molecules), their sensory properties, identified healthy and adverse effects, as well as the impact of processing on their bioavailability.

Application of Trichoderma Spp. Complex and Biofumigation to Control Damping-Off of Pinus Radiata D.Don Caused by Fusarium Circinatum Nirenberg and O’Donnell

The damping-off of Pinus radiata D.Don by Fusarium circinatum Nirenberg and O’Donnell represents a limiting factor in nursery production, while seed contamination with the pathogen is one of the main pathways of the pathogen movement between areas. Chemical and physical treatments have been applied with encouraging results and some limitations. In the present study, biocontrol of damping-off by F. circinatum is proposed with Trichoderma spp. complex showing complementary antagonism and biofumigation with commercial Brassica carinata A.Braun pellets with biocidal effect. Experiments were conducted in vitro and in vivo using batches of P. radiata seeds and two F. circinatum isolates. Results were highly positive, showing an excellent efficacy of a combination of Trichoderma spp. in a single preparation to reduce significantly the mortality of P. radiata seedlings in seeds bed experiment. Biofumigation with B. carinata pellets also showed efficacy in controlling the F. circinatum inoculum and reducing seed mortality in inoculated seed batches although showing some phytotoxic effect.

Disruption of microbial community composition and identification of plant growth promoting microorganisms after exposure of soil to rapeseed-derived glucosinolates

Land plants are engaged in intricate communities with soil bacteria and fungi indispensable for plant survival and growth. The plant-microbial interactions are largely governed by specific metabolites. We employed a combination of lipid-fingerprinting, enzyme activity assays, high-throughput DNA sequencing and isolation of cultivable microorganisms to uncover the dynamics of the bacterial and fungal community structures in the soil after exposure to isothiocyanates (ITC) obtained from rapeseed glucosinolates. Rapeseed-derived ITCs, including the cyclic, stable goitrin, are secondary metabolites with strong allelopathic affects against other plants, fungi and nematodes, and in addition can represent a health risk for human and animals. However, the effects of ITC application on the different bacterial and fungal organisms in soil are not known in detail. ITCs diminished the diversity of bacteria and fungi. After exposure, only few bacterial taxa of the Gammaproteobacteria, Bacteriodetes and Acidobacteria proliferated while Trichosporon (Zygomycota) dominated the fungal soil community. Many surviving microorganisms in ITC-treated soil where previously shown to harbor plant growth promoting properties. Cultivable fungi and bacteria were isolated from treated soils. A large number of cultivable microbial strains was capable of mobilizing soluble phosphate from insoluble calcium phosphate, and their application to Arabidopsis plants resulted in increased biomass production, thus revealing growth promoting activities. Therefore, inclusion of rapeseed-derived glucosinolates during biofumigation causes losses of microbiota, but also results in enrichment with ITC-tolerant plant microorganisms, a number of which show growth promoting activities, suggesting that Brassicaceae plants can shape soil microbiota community structure favoring bacteria and fungi beneficial for Brassica plants.

Control of Bradysia odoriphaga (Diptera: Sciaridae) With Allyl Isothiocyanate Under Field and Greenhouse Conditions

The botanical compound allyl isothiocyanate (AITC) is toxic to many microorganisms and insects. The aim of this study was to assess the effects of AITC on the Bradysia odoriphaga Yang et Zhang (Diptera: Sciaridae) and the seeds and seedlings of the Chinese chive. Allyl isothiocyanate was toxic to all four developmental stages of B. odoriphaga. The adult was significantly more sensitive to AITC than the other three stages, which exhibited no significant differences to one another in sensitivity to the chemical. The control efficacy of AITC against B. odoriphaga was far superior in the greenhouse than the field. In addition, seedling survival was higher in the greenhouse compared with that in the field. In the absence of B. odoriphaga, seed germination and seedling growth of Chinese chives were inhibited by 16 µl/liter of AITC, and significant inhibition occurred under higher doses of AITC. These results indicate that AITC could be used to control B. odoriphaga during cultivation of Chinese chives.

Allyl isothiocyanate shows promise as a naturally produced suppressant of the potato cyst nematode, Globodera pallida, in biofumigation systems

The ability of isothiocyanates to suppressGlobodera pallidawas evaluated throughin vitroassays. Several isothiocyanates increased juvenile mortality, the most effective being allyl isothiocyanate, which caused 100% mortality at both 25 and 50 ppm after 72 and 24 h exposure, respectively. In a hatching assay, allyl isothiocyanate was able to suppress hatch; in addition, replenishing allyl isothiocyanate every 3 days increased hatch suppression, and viability staining indicated that egg mortality was increased. Allyl isothiocyanate above concentrations of 50 ppm significantly affected both hatch suppression and mortality. Differing effects of isothiocyanates onG. pallidasuggest that their toxicity depends on the pest of interest and this study shows that allyl isothiocyanate is a good candidate for the control of potato cyst nematodes using biofumigation.

Factors Associated with Leguminous Green Manure Incorporation and Fusarium Wilt Suppression in Watermelon

Fall-planted Vicia villosa or Trifolium incarnatum cover crops, incorporated in spring as a green manure, can suppress Fusarium wilt (Fusarium oxysporum f. sp. niveum) of watermelon. During cover crop growth, termination, and incorporation into the soil, many factors such as arbuscular mycorrhizae colonization, leachate, and soil respiration differ. How these cover-crop-associated factors affect Fusarium wilt suppression is not fully understood. Experiments were conducted to evaluate how leachate, soil respiration, and other green-manure-associated changes affected Fusarium wilt suppression, and to evaluate the efficacy of the biocontrol product Actinovate AG (Streptomyces lydicus WYEC 108). General and specific suppression was examined in the field by assessing the effects of cover crop green manures (V. villosa, T. incarnatum, Secale cereale, and Brassica juncea) on soil respiration, presence of F. oxysporum spp., and arbuscular mycorrhizal colonization of watermelon. Cover crop treatments V. villosa, T. incarnatum, and S. cereale and no cover crop were evaluated both alone and in combination with Actinovate AG in the greenhouse. Additionally, in vitro experiments were conducted to measure the effects of cover crop leachate on the mycelial growth rates of F. oxysporum f. sp. niveum race 1 and Trichoderma harzianum. Soil microbial respiration was significantly elevated in V. villosa and Trifolium incarnatum treatments both preceding and following green manure incorporation, and was significantly negatively correlated with Fusarium wilt, suggesting that microbial activity was higher under the legumes, indicative of general suppression. Parallel to this, in vitro growth rates of F. oxysporum f. sp. niveum and Trichoderma harzianum on V. villosa leachate amended media were 66 and 213% greater, respectively, than on nonamended plates. The F. oxysporum spp. population (based on CFU and not differentiated into formae specialis or races) significantly increased in V. villosa-amended field plots. Additionally, the percentage of watermelon roots colonized by arbuscular mycorrhizae following V. villosa and Trifolium incarnatum green manures was significantly higher than in watermelon following bare ground (58 and 44% higher, respectively). In greenhouse trials where cover crops were amended to soil, Actinovate AG did not consistently reduce Fusarium wilt. Both general and specific disease suppression play a role in reducing Fusarium wilt on watermelon.

Bioavailability of Glucosinolates and Their Breakdown Products: Impact of Processing

Glucosinolates are a large group of plant secondary metabolites with nutritional effects, and are mainly found in cruciferous plants. After ingestion, glucosinolates could be partially absorbed in their intact form through the gastrointestinal mucosa. However, the largest fraction is metabolized in the gut lumen. When cruciferous are consumed without processing, myrosinase enzyme present in these plants hydrolyzes the glucosinolates in the proximal part of the gastrointestinal tract to various metabolites, such as isothiocyanates, nitriles, oxazolidine-2-thiones, and indole-3-carbinols. When cruciferous are cooked before consumption, myrosinase is inactivated and glucosinolates transit to the colon where they are hydrolyzed by the intestinal microbiota. Numerous factors, such as storage time, temperature, and atmosphere packaging, along with inactivation processes of myrosinase are influencing the bioavailability of glucosinolates and their breakdown products. This review paper summarizes the assimilation, absorption, and elimination of these molecules, as well as the impact of processing on their bioavailability.

Glutathione protects Candida albicans against horseradish volatile oil

Horseradish essential oil (HREO; a natural mixture of different isothiocyanates) had strong fungicide effect against Candida albicans both in volatile and liquid phase. In liquid phase this antifungal effect was more significant than those of its main components allyl, and 2-phenylethyl isothiocyanate. HREO, at sublethal concentration, induced oxidative stress which was characterized with elevated superoxide content and up-regulated specific glutathione reductase, glutathione peroxidase, catalase and superoxide dismutase activities. Induction of specific glutathione S-transferase activities as marker of glutathione (GSH) dependent detoxification was also observed. At higher concentration, HREO depleted the GSH pool, increased heavily the superoxide production and killed the cells rapidly. HREO and the GSH pool depleting agent, 1-chlore-2,4-dinitrobenzene showed strong synergism when they were applied together to kill C. albicans cells. Based on all these, we assume that GSH metabolism protects fungi against isothiocyanates.

Fusarium oxysporum f.sp. radicis-lycopersici induces distinct transcriptome reprogramming in resistant and susceptible isogenic tomato lines

BACKGROUND

Fusarium oxysporum f.sp. radicis-lycopersici (FORL) is one of the most destructive necrotrophic pathogens affecting tomato crops, causing considerable field and greenhouse yield losses. Despite such major economic impact, little is known about the molecular mechanisms regulating Fusarium oxysporum f.sp. radicis-lycopersici resistance in tomato.

RESULTS

A transcriptomic experiment was carried out in order to investigate the main mechanisms of FORL response in resistant and susceptible isogenic tomato lines. Microarray analysis at 15 DPI (days post inoculum) revealed a distinct gene expression pattern between the two genotypes in the inoculated vs non-inoculated conditions. A model of plant response both for compatible and incompatible reactions was proposed. In particular, in the incompatible interaction an activation of defense genes related to secondary metabolite production and tryptophan metabolism was observed. Moreover, maintenance of the cell osmotic potential after the FORL challenging was mediated by a dehydration-induced protein. As for the compatible interaction, activation of an oxidative burst mediated by peroxidases and a cytochrome monooxygenase induced cell degeneration and necrosis.

CONCLUSIONS

Our work allowed comprehensive understanding of the molecular basis of the tomato-FORL interaction. The result obtained emphasizes a different transcriptional reaction between the resistant and the susceptible genotype to the FORL challenge. Our findings could lead to the improvement in disease control strategies.

Inspired by Nature: The use of Plant-derived Substrate/Enzyme Combinations to Generate Antimicrobial Activity in situ

The last decade has witnessed a renewed interest in antimicrobial agents. Plants have received particular attention and frequently rely on the spontaneous enzymatic conversion of an inactive precursor to an active agent. Such two-component substrate/enzyme defence systems can be reconstituted ex vivo. Here, the alliin/alliinase system from garlic seems to be rather effective against Saccharomyces cerevisiae, whilst the glucosinolate/myrosinase system from mustard appears to be more active against certain bacteria. Studies with myrosinase also confirm that enzyme and substrate can be added sequentially. Ultimately, such binary systems hold considerable promise and may be employed in a medical or agricultural context.

Glucosinolate-derived isothiocyanates impact mitochondrial function in fungal cells and elicit an oxidative stress response necessary for growth recovery

Glucosinolates are brassicaceous secondary metabolites that have long been considered as chemical shields against pathogen invasion. Isothiocyanates (ITCs), are glucosinolate-breakdown products that have negative effects on the growth of various fungal species. We explored the mechanism by which ITCs could cause fungal cell death using Alternaria brassicicola, a specialist Brassica pathogens, as model organism. Exposure of the fungus to ICTs led to a decreased oxygen consumption rate, intracellular accumulation of reactive oxygen species (ROS) and mitochondrial-membrane depolarization. We also found that two major regulators of the response to oxidative stress, i.e., the MAP kinase AbHog1 and the transcription factor AbAP1, were activated in the presence of ICTs. Once activated by ICT-derived ROS, AbAP1 was found to promote the expression of different oxidative-response genes. This response might play a significant role in the protection of the fungus against ICTs as mutants deficient in AbHog1 or AbAP1 were found to be hypersensitive to these metabolites. Moreover, the loss of these genes was accompanied by a significant decrease in aggressiveness on Brassica. We suggest that the robust protection response against ICT-derived oxidative stress might be a key adaptation mechanism for successful infection of host plants by Brassicaceae-specialist necrotrophs like A. brassicicola.

Impact of Five Cover Crop Green Manures and Actinovate on Fusarium Wilt of Watermelon

Triploid watermelon cultivars are grown on more than 2,023 ha in Maryland and in Delaware. Triploid watermelon cultivars have little host resistance to Fusarium wilt of watermelon (Fusarium oxysporum f. sp. niveum). The effects of four different fall-planted cover crops (Vicia villosa, Trifolium incarnatum, Secale cereale, and Brassica juncea) that were tilled in the spring as green manures, and bare ground, were evaluated alone and in combination with the biocontrol product Actinovate (Streptomyces lydicus) on Fusarium wilt severity and watermelon fruit yield and quality. Six field experiments were conducted over 3 years in Beltsville and Salisbury, MD and Georgetown, DE. Both V. villosa and T. incarnatum significantly suppressed Fusarium wilt of watermelon as much as 21% compared with watermelon in nonamended plots. However, no suppression of Fusarium wilt occurred at low disease levels or where low cover crop biomass was present. In general, Beltsville, MD had lower disease levels than Salisbury, MD and Georgetown, DE. T. incarnatum was the only cover crop that yielded significantly more fruit than nonamended treatments (129% more fruit per hectare) but only for one field trial. The Actinovate product either did not reduce Fusarium wilt or the magnitude of the reduction was nominal. Actinovate significantly reduced Fusarium wilt by 2% in 2009 and as much as 7% in 2010, and increased Fusarium wilt severity by 2.5% in 2011. Actinovate significantly increased yield for one field trial but only when applied to nonamended or Secale cereal-amended plots. This is the first report of a reduction in Fusarium wilt following a T. incarnatum cover crop incorporated as a green manure.

Concentration- and time-dependent effects of isothiocyanates produced from Brassicaceae shoot tissues on the pea root rot pathogen Aphanomyces euteiches

Isothiocyanates (ITCs) hydrolyzed from glucosinolates (GSLs) in Brassicaceae tissue are toxic to soil organisms. In this study, the effect of aliphatic and aromatic ITCs from hydrated dry Brassicaceae shoot tissues on the mycelium and oospores of the pea root rot pathogen Aphanomyces euteiches was investigated. The profile and concentrations of GSLs in two test Brassicaceae species, Sinapis alba and Brassica juncea, and the ITCs from the dominant hydrolyzed parent GSLs were monitored. The concentrations of dominant ITCs and pathogen exposure time were evaluated in in vitro experiments. The greatest effect on the pathogen was observed from aliphatic ITCs hydrolyzed from B. juncea tissue, and the effect depended on the ITC concentration and exposure time. ITCs were more effectively hydrolyzed from B. juncea GSLs than from S. alba GSLs; i.e., the ITC/GSL ratio was higher in B. juncea than in S. alba tissue, giving a different release pattern. The release of phenylethyl isothiocyanate, which was common to both species, followed a pattern similar to that of the dominant ITC in each crop species. This suggests that traits other than GSL content, e.g., plant cell structure, may affect the release of ITCs and should therefore influence the choice of species used for biofumigation purposes.

Control of Phytophthora nicotianae with Mefenoxam, Fresh Brassica Tissues, and Brassica Pellets

Sensitivity to mefenoxam, fresh Brassicaceae tissues, and Brassica pellets was evaluated in several isolates of Phytophthora nicotianae recovered from pepper and tomato plants. The isolates of P. nicotianae studied were classified as sensitive to mefenoxam, showing great variability among isolates in the 50 and 90% effective concentrations (EC₅₀ and EC₉₀, respectively). Sensitivity differentiated isolates from the two hosts of origin, being isolates from tomato plants more resistant to fungicide than those from pepper plants. This differentiation also occurred in the case of fresh Brassicaceae tissues assay. The most effective biofumigant in inhibiting mycelial growth of P. nicotianae isolates was Brassica nigra. The effectiveness of B. carinata, Sinapis alba, and B. oleracea varied depending on the dose. Isolates differed in susceptibility to compounds released by the Brassica pellets and then in the EC₅₀ and EC₉₀. No significant difference was found between the isolates depending on the host of origin. Greenhouse tests demonstrated the effectiveness of treatments with mefenoxam and with Brassica pellets to control P. nicotianae in pepper plants. Mefenoxam application could be a solution to the disease caused by P. nicotianae in tomato and pepper crops in this region but its use could increase resistance in populations. Biofumigation is a promising technique which can be further developed to form part of integrated pest management strategies.

Verticillium suppression is associated with the glucosinolate composition of Arabidopsis thaliana leaves

The soil-borne fungal pathogen Verticillium longisporum is able to penetrate the root of a number of plant species and spread systemically via the xylem. Fumigation of Verticillium contaminated soil with Brassica green manure is used as an environmentally friendly method for crop protection. Here we present a study focused on the potential role of glucosinolates and their breakdown products of the model plant Arabidopsis thaliana in suppressing growth of V. longisporum. For this purpose we analysed the glucosinolate composition of the leaves and roots of a set of 19 key accessions of A. thaliana. The effect of volatile glucosinolate hydrolysis products on the in vitro growth of the pathogen was tested by exposing the fungus to hydrated lyophilized plant tissue. Volatiles released from leaf tissue were more effective than from root tissue in suppressing mycelial growth of V. longisporum. The accessions varied in their efficacy, with the most effective suppressing mycelial growth by 90%. An analysis of glucosinolate profiles and their enzymatic degradation products revealed a correlation between fungal growth inhibition and the concentration of alkenyl glucosinolates, particularly 2-propenyl (2Prop) glucosinolate, respectively its hydrolysis products. Exposure of the fungus to purified 2Prop glucosinolate revealed that its suppressive activity was correlated with its concentration. Spiking of 2Prop glucosinolate to leaf material of one of the least effective A. thaliana accessions led to fungal growth suppression. It is suggested that much of the inhibitory effect observed for the tested accessions can be explained by the accumulation of 2Prop glucosinolate.

Engineering glucosinolates in plants: current knowledge and potential uses

Glucosinolates (GSL) and their derivatives are well known for the characteristic roles they play in plant defense as signaling molecules and as bioactive compounds for human health. More than 130 GSLs have been reported so far, and most of them belong to the Brassicaceae family. Several enzymes and transcription factors involved in the GSL biosynthesis have been studied in the model plant, Arabidopsis, and in a few other Brassica crop species. Recent studies in GSL research have defined the regulation, distribution, and degradation of GSL biosynthetic pathways; however, the underlying mechanism behind transportation of GSLs in plants is still largely unknown. This review highlights the recent advances in the metabolic engineering of GSLs in plants and discusses their potential applications.

In vitro inhibition of mycelial growth of Phytophthora nicotianae Breda de Haan from different hosts by Brassicaceae species. Effect of the developmental stage of the biofumigant plants

BACKGROUND

The hydrolysis products of glucosinolates in Brassicaceae tissues are potentially useful for the control of fungal pathogens. The in vitro activity of these products against Phytophthora nicotianae Breda de Haan was studied, with the isolates exposed to the volatile products released from the brassica tissues.

RESULTS

The four species of Brassicaceae tested inhibited the mycelial growth of P. nicotianae isolates. The most effective developmental stage was different, depending on the species: buds yellowing in Sinapis alba L. and Brassica carinata A. Braun; seeds enlarging and all buds open in Brassica nigra (L.) W.D.J. Koch; cauliflower still covered by leaves in Brassica oleracea L. var. botrytis. At this stage, B. nigra and S. alba were the most effective (53.6 and 52.5% inhibition respectively). With all the biofumigants species tested, isolates from pepper plants were more susceptible to the brassica effect than those from tomato isolates.

CONCLUSION

The developmental stage of plants has an influence on the biofumigant potential of Brassicaceae species against P. nicotianae. The isolates differ in susceptibility to compounds released, depending on their host of origin, suggesting the differentiation of populations of P. nicotianae in relation to the host of origin.

Allyl isothiocyanate induced stress response in Caenorhabditis elegans

BACKGROUND

Allyl isothiocyanate (AITC) from mustard is cytotoxic; however the mechanism of its toxicity is unknown. We examined the effects of AITC on heat shock protein (HSP) 70 expression in Caenorhabditis elegans. We also examined factors affecting the production of AITC from its precursor, sinigrin, a glucosinolate, in ground Brassica juncea cv. Vulcan seed as mustard has some potential as a biopesticide.

FINDINGS

An assay to determine the concentration of AITC in ground mustard seed was improved to allow the measurement of AITC release in the first minutes after exposure of ground mustard seed to water. Using this assay, we determined that temperatures above 67°C decreased sinigrin conversion to AITC in hydrated ground B. juncea seed. A pH near 6.0 was found to be necessary for AITC release. RT-qPCR revealed no significant change in HSP70A mRNA expression at low concentrations of AITC (< 0.1 μM). However, treatment with higher concentrations (> 1.0 μM) resulted in a four- to five-fold increase in expression. A HSP70 ELISA showed that AITC toxicity in C. elegans was ameliorated by the presence of ground seed from low sinigrin B. juncea cv. Arrid.

CONCLUSIONS

• AITC induced toxicity in C. elegans, as measured by HSP70 expression.• Conditions required for the conversion of sinigrin to AITC in ground B. juncea seed were determined.• The use of C. elegans as a bioassay to test AITC or mustard biopesticide efficacy is discussed.

Use of brassica plants in the phytoremediation and biofumigation processes

In recent decades, serious contamination of soils by heavy metals has been reported. It is therefore a matter of urgency to develop a new and efficient technology for removing contaminants from soil. Another aspect to this problem is that environmental pollution decreases the biological quality of soil, which is why pesticides and fertilizers are being used in ever-larger quantities. The environmentally friendly solutions to these problems are phytoremediation, which is a technology that cleanses the soil of heavy metals, and biofumigation, a process that helps to protect crops using natural plant compounds. So far, these methods have only been used separately; however, research on a technology that combines them both using white cabbage has been carried out.

In vitro and in vivo antifungal activity of synthetic pure isothiocyanates against Sclerotinia sclerotiorum

BACKGROUND

Isothiocyanates (ITCs) released by the enzymatic hydrolysis of glucosinolates in the Brassicaceae are potentially useful for controlling fungal pathogens. In vitro activity of pure ITCs against Sclerotinia sclerotiorum (Lib.) de Bary was studied by adding them to glass filters in petri dishes and dissolving them in the growing media.

RESULTS

Methyl, allyl and benzyl ITCs were the most fungitoxic of the compounds in bioassays with S. sclerotiorum isolate Ss31. In the volatile phase, mycelial growth was completely inhibited by these three compounds. Aromatic ITCs were less toxic in the petri dishes but were more toxic than aliphatic ITCs when dissolved in the agar. Benzyl ITC exhibited the highest inhibitory effect on sclerotial germination, with an EC(50) value of 75.1 µmol L(-1) . Butyl and benzyl ITCs reduced apothecial production of S. sclerotiorum by 92.5% at the highest concentration. In in vivo assay, only allyl and 2-phenylethyl ITCs reduced disease incidence (by 76.7 and 70% respectively) at low concentrations.

CONCLUSION

Sclerotinia sclerotiorum in the soil might be suppressed by the higher concentrations of allyl and benzyl ITCs released from decomposition of Brassica juncea, B. carinata, B. nigra and Sinapis spp.

Phenological and phytochemical changes correlate with differential interactions of Verticillium dahliae with broccoli and cauliflower

Cauliflower (Brassica oleracea var. botrytis subvar. cauliflora) is susceptible to wilt caused by Verticillium dahliae but broccoli (B. oleracea var. italica subvar. cyamosa) is not. Infection of broccoli and cauliflower by a green fluorescent protein-expressing isolate of V. dahliae was examined using epifluorescence and confocal laser-scanning microscopy to follow infection and colonization in relation to plant phenology. Plant glucosinolate, phenolic, and lignin contents were also assayed at 0, 4, 14, and 28 days postinoculation. V. dahliae consistently infected and colonized the vascular tissues of all cauliflower plants regardless of age at inoculation, with the pathogen ultimately appearing in the developing seed; however, colonization decreased with plant age. In broccoli, V. dahliae infected and colonized root and stem xylem tissues of plants inoculated at 1, 2, or 3 weeks postemergence. However, V. dahliae colonized only the root xylem and the epidermal and cortical tissues of broccoli plants inoculated at 4, 5, and 6 weeks postemergence. The frequency of reisolation of V. dahliae from the stems (4 to 22%) and roots (10 to 40%) of mature broccoli plants was lower than for cauliflower stems (25 to 64%) and roots (31 to 71%). The mean level of aliphatic glucosinolates in broccoli roots was 6.18 times higher than in the shoots and did not vary with age, whereas it was 3.65 times higher in cauliflower shoots than in the roots and there was a proportional increase with age. Indole glucosinolate content was identical in both cauliflower and broccoli, and both indole and aromatic glucosinolates did not vary with plant age in either crop. Qualitative differences in characterized glucosinolates were observed between broccoli and cauliflower but no differences were observed between inoculated and noninoculated plants for either broccoli or cauliflower. However, the phenolic and lignin contents were significantly higher in broccoli following inoculation than in noninoculated broccoli or inoculated cauliflower plants. The increased resistance of broccoli to V. dahliae infection was related to the increase in phenolic and lignin contents. Significant differential accumulation of glucosinolates associated with plant phenology may also contribute to the resistant and susceptible reactions of broccoli and cauliflower, respectively, against V. dahliae.

Differentially expressed cDNAs in Alternaria alternata treated with 2-propenyl isothiocyanate

The molecular mechanism of the fungal tolerance phenotype to fungicides is not completely understood. This knowledge would allow for the development of environmentally friendly strategies for the control of fungal infection. With the goal of determining genes induced by 2p-ITC, a forward suppressive subtractive hybridization was performed using cDNAs from ITC-treated Alternaria alternata as a "tester" and from untreated fungus as a "driver." Using this approach, a library containing 102 ESTs was generated that resulted in 50 sequences after sequence assembly (17 contigs and 33 singletons). Blastx analysis revealed that 38% and 40% of the sequences showed significant similarity with known and hypothetical proteins, respectively, whereas 18% were not similar to known genes. These last sequences could represent novel genes that play an unknown role in the molecular responses of fungi during adaptation to 2p-ITC. Clones similar to opsins, ABC transporters, calmodulin, ATPases and SNOG proteins were identified. Using real-time RT-PCR analysis, significant inductions of an ABC transporter and a Ca(++) ATPase during 2p-ITC treatment were discovered. These results suggest that the fungal resistance phenotype to 2p-ITC involves calcium ions and 2p-ITC efflux via an ABC transporter.

Effect of Incorporation of Brassica spp. Residues on Population Densities of Soilborne Microorganisms and on Damping-off and Fusarium Wilt of Watermelon

Incorporating Brassica spp. residue to reduce populations of soilborne fungi and manage damping-off and Fusarium wilt of watermelon (Citrullus lanatus var. lanatus) was studied in two field experiments. Treatments included incorporating flowering Brassica napus cv. Dwarf Essex canola or B. juncea cv. Cutlass mustard and laying black polyethylene mulch at incorporation or 1 month after incorporation, methyl bromide, and a nontreated control. In both years, glucosinolates were identified and quantified in the shoots and roots of the flowering plants. In both years, the total concentration of glucosinolates incorporated per square meter was significantly higher for B. juncea than for B. napus. Isothiocyanates were inconsistently detected in the amended soils and none were detected more than 12 days postincorporation. After incorporation in 2004 and 2005, amended plots had higher populations of Fusarium oxysporum and Pythium spp. than the methyl bromide treatment, and in some treatments, populations were higher than in the control. Fluorescent Pseudomonas spp. were not suppressed in amended soils, and their populations were significantly higher in some amended treatments than those in methyl bromide-treated soils or nontreated control soils. Incidence of damping-off and severity of Fusarium wilt on seedless watermelon cv. Tri-X 313, which is susceptible to Fusarium wilt, were not consistently lower in brassica-amended soils or methyl bromide-treated plots than in nontreated control plots. Therefore, under spring conditions and methods used in this study, neither biofumigation nor methyl bromide fumigation in coastal South Carolina was an effective disease management tool for two soilborne pathogens of watermelon.

Facts and fiction about sulfur metabolism in relation to plant-pathogen interactions

Sulfur deficiency developed into a widespread nutrient disorder in the 1980s because of the drastic decrease of SO(2) emissions in western Europe after Clean Air Acts came into force. It was observed that not only the yield and quality of agricultural crops were negatively affected by sulfur deficiency but also their health status. Since the mid 1990s the physiological background of this latter phenomenon in the sulfur metabolism has been studied by different researchers. From 2001 until 2006, field trials with different varieties of oilseed rape were conducted in Germany, and also from 2001 until 2003 in Scotland, to investigate the underlying mechanisms of sulfur-induced resistance and to develop fertiliser strategies which increase the health status of crops and minimise the requirement for chemical fungicides. A comprehensive disease assessment was conducted and a range of different sulfur-containing metabolites and enzymes were analysed in relation to sulfur nutrition and fungal diseases. H2S emissions from field-grown crops under different sulfur nutritional status were studied for the first time and a positive relationship was observed. Besides S fertilisation, fungal infection increased H2S emissions, too. The studies deliver new insight into the complex of sulfur-induced resistance but many questions still remain open. This contribution will show different possible strategies to solve some of the open questions.

Formation and degradation kinetics of the biofumigant benzyl isothiocyanate in soil

Glucosinolates (GSLs) are produced by plants of the Capparales order. Upon enzymatic hydrolysis the GSLs can be transformed to the toxic isothiocyanates (ITCs), which can be used as biofumigants for the control of soil-borne pests. The rates of ITC formation and degradation are critical to both biofumigation and the toxicity and leaching of GSLs and ITCs in soil. Degradation kinetics of benzyl GSL and benzyl ITC in a sandy and clayey surface and subsoil at 8-9 degrees C at natural moisture contents were investigated, as was the rate of formation of ITC from the GSL. Degradation of GSL followed logistic kinetics with t 1/2 = 0.7-9.1 days. Degradation was faster in clayey soil compared to sandy soil, and faster in surface soil compared to subsoil. In surface soils, up to 25% of added GSL was detected as ITC, while only 1-6% were detected in the subsoils. ITC degradation followed first-order kinetics with t 1/2 = 0.3-1.7 days, with faster degradation in subsoils than in surface soils. Based on the data for GSL hydrolysis and ITC degradation, the concentration of ITC following GSL application was successfully modeled assuming complete conversion of glucosinolate to isothiocyanate and first-order degradation of isothiocyanate.