Brassica Tissues Research Articles

Systemic biochemical changes in pepper (Capsicum annuum L.) against Rhizoctonia solani by kale (Brassica oleracea var. acephala L.) green manure application

BackgroundIn the search for new alternatives to avoid the problems associated with the use of synthetic chemical fungicides in agriculture, the use of green manure (GrM) could help combat fungal diseases of crops, such as those produced by the necrotrophic pathogen Rhizoctonia solani. In the case of the use of Brassica tissues as GrM, it could have an elicitor capacity for systemic plant resistance.ResultsWe used kale leaves as a GrM and applied it to pepper plants infected with R. solani. The application of freeze-dried kale tissues to the roots of pepper plants produced a systemic activation of foliar defences via the salicylic acid (SA) and ethylene (ET) pathways, significantly reducing pathogen damage. In addition, this systemic response led to the accumulation of secondary defence metabolites, such as pipecolic acid, hydroxycoumarin and gluconic acid, in leaves. Remarkably, pepper plants treated with lyophilised kale GrM accumulated glucosinolates when infected with R. solani. We also confirmed that autoclaving removed part of the glucobrassicin (85%) and sinigrin (19%) content of the kale tissues.ConclusionsGrM kale tissues can activate systemic defences in bell pepper against foliar pathogens through SA/ET hormonal pathways, accumulating secondary defence metabolites.

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.

A Review of Bio-Role Fumigation's in Plant Parasitic Nematode (PPNs) Control

Worldwide there are greater than 4,100 species of PPNs. The most common opponent of agricultural production is PPNs. Plant parasitic nematodes (PPN) cause substantial economic destruction to an extensive range of crops. Nematicide Chemicals are considered the furthermost operative method in reducing nematodes population. Increasing concern over chemical nematicides has increased interest in safe alternative methods to minimize these losses. This review focuses on the role of bio-fumigation against PPNs in sustainable agroecosystems. Bio-fumigation is a long-term approach for controlling diseases, nematodes, insects, and weeds in the soil. It was originally defined as the pest-controlling effect of decomposing Brassica tissues, but it was later broadened to include animal and plant leftovers. Glucosinolates are the principal active molecule responsible for the bio-fumigation process in various plants. Plant age and tissue type influence glucosinolate accumulation and myrosinase activity, which are influenced by environmental factors such as planting density and herbivory. Glucosinolates are sulphur-containing chemicals produced by the secondary metabolism of plants in the order Capparales, which includes the Brassicacea family among others. Natural antimicrobials and anti-carcinogenic agents, glucosinolates are well-known. Therefore, researchers should have to focus on environmentally save methods of plant parasitic nematode management like bio-fumigation. This biofumigation may be replace the fumigant nematicides for future.

Effect of Biofumigation on Fusarium wilt of Eggplant caused by Fusarium oxysporum f. sp. melongenae

Eggplant is the most traditional vegetable crop in India and susceptible to a number of diseases, among which Fusarium wilt caused by Fusarium oxysporum f.sp. melongenae (FOM) that reduce yield and quality. The present study on effect of biofumigation on Fusarium wilt of eggplant caused by Fusarium oxysporum f.sp. melongenae under natural field conditions showed that the biocidal volatiles released by Brassica tissue incorporation decreased the wilt incidence greatly from 14.57(Radish) to 50.88(Mustard) per cent reduction over control and significantly enhanced the Yield 30.43 (Radish) to 51.95 (Mustard) per cent increase over control and also enhanced the yield parameters viz., leaf area (10.15 to 35.87), plant height(13.01 to 26.39), root length(23.10 to 49.29) per cent increase over control respective.

Effect of Field Treatment with Selected Soil Amendments on Bacterial Wilt Incidences in Tomatoes, Capsicum and Potatoes

Aims: The aim of this study was to establish the effect of field treatment with selected soil amendments on bacterial wilt incidences in Tomatoes, Capsicum and Potatoes. 
 Study Design: The study was laid out as randomized complete block design (RCBD) in split plot arrangement for two seasons in the field.
 Place and Duration of Study: The experiment was conducted at the experimental plots at KARLO- NARL, Kabete Nairobi County between July, 2017- September, 2017 and between November, 2017- January, 2018.
 Methodology: The three choice crops of interest (potatoes, tomatoes and capsicum) were inoculated with prepared pure bacterial isolates; 18 (2T-Kiambu-Low Land), 71(2A-Nyeri-Low Land), 67 (2A-Nyeri-High Land), 83 (2T-Kirinyaga-Highland) and MX (18/71/67/83). A plot measuring 66 m by 28.5 m was marked, cleared, ploughed, harrowed and demarcated into 150 plots each measuring 2.4 m x 3.75 m. Spacing of the host crops of interest: potato - (Tigoni variety), tomato (Caj variety) and capsicum (Califonia Wonder) was carried out at 75 cm between the rows and 30 cm within the rows. The treatments were ChalimTM, Super-hydro-grow polymer + Metham sodium, Metham sodium, Metham sodium & Orange peel, Super-hydro-grow polymer, Brassica tissues, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel, Metham sodium + Super-hydro-grow polymer and Control (no amendments).
 Results: Significant differences (P≤0.05) were revealed in the bacterial wilt incidences in tomatoes, capsicum and potatoes between control and all the soil amendments used in season 1 and 2 in the five R. solanacearum isolate from Kenyan highlands and lowlands. The Brassica tissue + Super-hydro-grow polymer was superior in reducing bacterial wilt incidences in tomatoes, capsicum and potatoes in the field in all the R. solanacearum isolates from Kenyan highlands and lowlands both in season 1 and 2.
 Conclusion: The findings showed that organic and inorganic soil amendments could serve as a viable control of bacterial wilt in solanaceous crops caused by R. solanacearum in the field. We recommend the use of Brassica tissue + Super-hydro-grow polymer soil amendment in the control of bacterial wilt incidences in the field on solanaceous crops.

Influence of Organic and Inorganic Soil Amendments on Soil Moisture Content and Micronutrients

Aims: This study was carried out to evaluate the influence of organic and inorganic soil amendments on soil moisture content and micronutrients in semi and arid areas. 
 Methodology: The study was laid out as randomized complete block design (RCBD) in split plot arrangement for two seasons. The treatments were ChalimTM, Super-hydro-grow polymer and Metham sodium, Metham sodium, Metham sodium + Orange peel, Super-hydro-grow polymer, Control, Brassica tissue, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel and Metham sodium + Super-hydro-grow polymer. Soils were sampled from each experimental site, dried and taken to laboratories for determination of Zinc, Iron, Manganese and copper both at initial and at the end of the experiment using a SpectrAA- 40 atomic absorption spectrometer, PSC-56 programmable sample changer. Moisture content was calculated by subtracting total dry soil plus Petri dish weight from total wet soil plus Petri dish weight. Calculated moisture content was recorded in all samples across the two seasons for analysis.
 Results: There was a significant difference (p≤0.05) in the treatment effect on soil moisture content in except for MS and CM+OP in both season one and season two in the green house. A combination of both organic and inorganic soil amendments like BT+OP, BT+ SHG had the highest moisture content. There was significant difference (p≤0.05) in the soil amendments effect on the amount of Micronutrients in the beginning and end of the experiement.
 Conclusion: Through this study, it was realized significant difference (p≤0.05) in the soil amendments effect on soil moisture content in all the treatment in both seasons. BT +SHG soil amendment was superior in maintaining soil moisture content in both season 1 and 2. It is therefore recommended that Metham sodium should not be applied in very dry soil to avoid reduction of the moisture content. There was micronutrient increment in all the treatments. BT+ SHG was superior soil amendment in increment of micronutrients.

Detection of Xanthomonas campestris pv. campestris through a real-time PCR assay targeting the Zur gene and comparison with detection targeting the hrpF gene

Xanthomonas campestris pv. campestris (Xcc) is a seedborne bacterium that causes black rot of crucifers. A real-time PCR assay based on a dual-labeled hydrolysis TaqMan® probe has been developed for the rapid and sensitive detection of Xcc and related pathovars that affect mainly Brassicaceae crops and ornamentals. Primers were designed to specifically amplify a 152 bp fragment of the Zur gene from X. campestris. To confirm the specificity of the detection, primers targeting the Zur and hrpF genes were used for standard and real-time PCR with DNA samples from 13 Xcc strains, seven Xanthomonas species and pathovars and five different bacterial endophytes including Bacillus, Erwinia, Klebsiella, Pantoea and Pseudomonas, previously isolated from tissues of crucifers. PCR products amplified with Zur and hrpF primers were sequenced to assess the genetic diversity of these genes in the tested isolates. The real-time PCR protocol was optimized to allow the detection at the level of ten copies of Zur PCR fragment per one microliter of DNA. Although the real-time based on detection of Zur also detected X. campestris pvs raphani, armoraciae, incanae and a strain of X. hortorum pv. carotae, it improved the specificity in relation to the previously published hrpF based real-time method. A multiplex assay for Zur and hrpF genes further improved the specificity by excluding X. hortorum pv. carotae. Tests of brassica tissues and seeds artificially inoculated with Xcc showed that the real-time PCR based on detection of Zur is an efficient and robust assay.

Control of Ralstonia solanacearum on Selected Solaneceous Crops in Greenhouse by Selected Soil Amendments

Aims: The aim of this study was to establish the effect of selected soil amendments on Ralstonia solanacearum isolates in greenhouse on selected solaneceous crops.
 Study Design: The study was laid out as randomized complete block design (RCBD) in split pot arrangement for two seasons in the greenhouse.
 Place and Duration of Study: The experiment was carried out in Kenyattta University situated in Kiambu County about 20 km from Nairobi city along Nairobi-Thika road between July, 2017- September, 2017 and between November, 2017- January, 2018.
 Methodology: The three host crops of interest (potatoes, tomatoes and capsicum) were inoculated with prepared pure bacterial isolates; 18 (2T-Kiambu-Low Land), 71(2A-Nyeri-Low Land), 67 (2A-Nyeri-High Land), 83 (2T-Kirinyaga-Highland) and MX (18/71/67/83). Potatoes, tomatoes and capsicum were planted in pots each with a radius of 0.07 m (area 0.015 m2).The experiment had a total of 450 pots having a total area of 6.93 m2. The treatments were ChalimTM, Super-hydro-grow polymer + Metham sodium, Metham sodium, Metham sodium & Orange peel, Super-hydro-grow polymer, Brassica tissues, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel, Metham sodium + Super-hydro-grow polymer and Control (no amendments).
 Results: There were significant differences (P≤0.05) in the bacterial wilt incidences in selected solaneceous crops between control and all the soil amendments used in season 1 and 2. Brassica tissue + Super-hydro-grow polymer was superior in reducing bacterial wilt incidences in selected solaneceous crops in all the R. solanacearum isolates from Kenyan highlands and lowlands both in season 1 and 2.
 Conclusion: Organic and inorganic soil amendments could serve as a viable control of bacterial wilt in solaneceous crops caused by R. solanacearum in the greenhouse.

Influence of Organic and Inorganic Soil Amendments on Soil pH and Macronutrients

The popularity of using the Inorganic and organic soil amendments is based on the current status of soil degradation that led to decline in fertility of soils, resulting to low yields. The objective of current study was to evalute different organic and inorganic soil amendments and their effects on soil pH and macronutrients. The study was laid out as randomized complete block design (RCBD) in split plot arrangement for two seasons. The treatments were ChalimTM, Super-hydro-grow polymer + Metham sodium, Metham sodium, Metham sodium & Orange peel, Super-hydro-grow polymer, Brassica tissues, ChalimTM + Super-hydro-grow polymer, Brassica tissue + Orange peel, Metham sodium + Super-hydro-grow polymer and Control (no amendments). Soils were sampled from each experimental site, dried and taken to laboratories for determination of soil chemical properties both at initial and at the end of the experiment. The soil physicochemical attributes assessed included: Soil pH, nitrogen, carbon, phosphorus, potassium and calcium. There was an significant increase (P≤0.05) in the concentration and availability of soil physicochemical characteristics after treatment which is an indicator of improved soil structure. Brassicae tissue +super hydrogrow polymer (BT+SHG) amendment was the best as it resulted to highest concentration and availability of the mineral elements in the soil recording total nitrogen of 0.50 %, organic carbon 5.47 %, phosphorus 19.7 mg/kg, and potassium 1.37 %. The control exhibited the least impact on all the soil chemical properties. We recommend BT+SHG amendment to farmers to promote soil fertility which will consequently produce better yield.

Can Incorporating Brassica Tissues into Soil Reduce Nitrification Rates and Nitrous Oxide Emissions?

New Zealand agriculture is composed predominantly of pastoral grazing systems; however, forage crops have been increasingly used to supplement the diet of grazing animals. Excreta from grazing animals has been identified as a main contributor of NO emissions. Some forage crops, such as brassicas ( spp.), contain secondary metabolites that have been identified to inhibit soil N cycling processes, and nitrification in particular. Our objective was to determine if secondary metabolites released from brassica tissues inhibited nitrification and reduced NO emissions when incorporated into soil, which was amended with a large amount of urea N (such as derived from urine patches deposited during grazing). Three brassica tissues (kale [ L.], turnip [ L.] bulb, and turnip leaf and stem) and ryegrass ( L.) tissue were incorporated into soil with and without urea solution, and NO, NO, and NH were measured during a 52-d incubation. All brassica tissues reduced urea-derived NO emissions relative to ryegrass tissues when incorporated into soil. According to the mineral N and microbial community data, this reduction, however, could not be attributed to inhibition of nitrification. Although there was less NO from urea in the brassica treatments, total NO emissions increased after incorporation of all tissue residues into soil, so this tradeoff must be explored if brassica tissues are to be considered as a tool for NO reduction.

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

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. 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. 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.

Loss of soil microbial diversity may increase insecticide uptake by crop

Belowground biodiversity is essential for soil functioning, but the effect of belowground biodiversity loss on food safety is unknown. We investigated the loss of soil microbial diversity on insecticides accumulation in Brassica. We manipulated soil biodiversity using the dilution-to-extinction approach in a Brassica-soil-insecticide system, monitored microbial communities via high-throughput sequencing, and identified potential functional microbes. Compared with unsterilized soil, the richness of functional bacteria was reduced by 14.1%, 36.2%, 51.6% and 73.2%, respectively, in the corresponding sterilized soil inoculated with 1-, 10−2-, 10−4- and 10−6-fold diluted soil suspension. The acetamiprid and imidacloprid concentrations increased significantly in Brassica tissues grown in sterilized soil inoculated with 10−6-fold diluted suspension. A bacterial group predominated in functional microbes of soils inoculated with 1-, 10−2- or 10−4-fold diluted suspension, but the relative abundance declined in soil inoculated with a 10−6-fold diluted suspension. Our findings revealed that undesirable impacts by the loss of soil biodiversity at an intermediate level on the accumulation of soil contaminant in plants could be alleviated by microbial functional redundancy through disproportionally complementary growth of specific functional microbial taxa, but severe loss of soil biodiversity would threaten food safety.

Effects of Cabbage Tissue and Calcium Hypochlorite on Soil Fertility and Yields of Selected Solanaceous Crops

The objective of this study was to determine the effect of inorganic compounds treatment(s) namely: Chalim (CM), a chlorine-containing compound, metham sodium (MS) (positive control) and Co (negative control) versus organic compound such as Brassica tissue treatment (BT), on soil pH, micro and macroelements. Three levels of Chalim and that of Brassica tissue; one of MS and one for Co were used. The test crops included were; Tomato, capsicum and potato. All the plots were inoculated with R. solanacearum to a level of approximately 7.5×10 Colony forming unit (CFU) per plot. Soil samples were taken using zigzag method after which the selected parameter levels were determined at the beginning and at the end of each season for three seasons (2009-2010). The amendments were prepared and applied in the field plots measuring (4.5×2.7 M) in randomized complete block design at Kenya agricultural research institute National agricultural laboratories in plant pathology section and Department of Plant and Microbial Sciences, Kenyatta university. The effects of the soil amendments on soil physico-chemical properties and yields were determined. The findings established that, Brassica tissue, at highest level of Review Article Annual Research & Review in Biology, 4(3): 547-559, 2014 548 application was the best soil amendment to be incorporated since more nutrients and yields were realized at that treatment as compared to the others. The various treatments differed significantly on their effect on the total yields. In tomato, the various treatments differed significantly (P<0.05) with plants grown on MS200 and BT5292 having significantly higher yields than the control. The study revealed that BT5292 increased the soil pH, yields, Nitrogen content, organic carbon, calcium and potassium concentration as compared to the other treatments and the control.

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.

Toxicity of hydrolysis volatile products of Brassica plants to Sclerotinia sclerotiorum, in vitro

Oilseed rape stem rot disease caused by Sclerotinia sclerotiorum causes serious yield losses worldwide. Glucosinolates as specific secondary metabolites of Brassicaceae are produced in various parts of the host plants. Their enzymatic hydrolysis releases chemical components, particularly isothiocyanates, with fungitoxic activity and volatile characteristics. To investigate the effect of volatiles derived from Brassica tissues, the pathogen was exposed to hydrolysis products of Brassica shoot parts as sources of glucosinolates including oilseed rape varieties and two species, black and white mustard. The results showed significant differences in inhibition of S. sclerotiorum growth between varieties and species. All tissues of black mustard inhibited completely the exposed colonies of the pathogen and oilseed rape varieties Dunkeld, Oscar and Rainbow had significant inhibitory effect on the fungus. The genotypes demonstrated significant differences for the production of toxic volatiles, indicating that GSL contents in Brassica species and even cultivars have different potentials for toxic products.

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

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. 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. 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.

The Isolation and Determination of Sulforaphane from Broccoli Tissues by Reverse Phase‐High Performance Liquid Chromatography

AbstractSulforaphane is a cognate isothiocyanate of glucoraphanin, released by degradation of glucosinolate through myrosinase enzyme, when Brassica tissues are crushed or chewed. C8 analytical column and mixture of water/acetonitrile 65/35 (ν/ν) as mobile phase were used to separate sulforaphane in broccoli tissues (e.g., 7‐day‐seedling, seed, floret and leave). Confirmation of sulforaphane in crude extract of broccoli tissues was monitored using gas chromatography‐mass spectroscopy (GC‐MS). The highest amount of sulforaphane (1216 μg/g dry weight) found in 7‐day‐seedling. This method is suitable for routine screening of plant materials and proposes a low cost and robust technique for the analysis of sulforaphane.

Effect of soil amendments and biological control agents (BCAs) on soil-borne root diseases caused by Pyrenochaeta lycopersici and Verticillium albo-atrum in organic greenhouse tomato production systems

The effect of different soil amendments and biological control agents on soil-borne root diseases that cause significant economic losses in organic and other soil-based tomato production systems (Pyrenochaeta lycopersici and Verticillium albo-atrum) was compared. Organic matter inputs (fresh Brassica tissue, household waste compost and composted cow manure) significantly reduced soil-borne disease severity (measured as increased root fresh weight) and/or increased tomato fruit yield, with some treatments also increasing fruit number and/or size. Soil biological activity also increased with increasing organic matter input levels and there were significant positive correlations between soil biological activity, root fresh weight and fruit yield. This indicates that one mechanism of soil-borne disease control by organic matter input may be increased competition by the soil biota. Chitin/chitosan products also significantly reduced soil-borne disease incidence and increased tomato fruit yield, number and/or size, but had no effect on soil biological activity. Biological control products based on Bacillus subtilis and Pythium oligandrum and commercial seaweed extract (Marinure) and fish emulsion (Nugro)-based liquid fertilisers had no positive effect on soil-borne disease incidence and fruit yield, number and size. The use of ‘suppressive’ organic matter inputs alone or in combination with chitin/chitosan soil amendments can therefore be recommended as methods to control soil-borne diseases in organic and other soil-based production systems.

HPLC-ICP-MS and ESI-Q-TOF analysis of biomolecules induced in Brassica juncea during arsenic accumulation

Arsenic (As) bioaccumulation by plants can be used as a strategy to detoxify arsenic polluted sites. Genetic engineering may provide a means of optimizing this natural process to increase its efficiency. However, this approach requires a thorough understanding of As metabolism and detoxification in plants. Identifying As-containing metabolites in plants is an important first step in elucidating As metabolism. Brassica juncea (Indian mustard) is studied here as a model for As accumulation in terms of total metalloid accumulation and its elemental speciation. A study on extraction conditions using 25 mM ammonium acetate buffer at increasing pH of 4.4, 5.6 and 7.8 has been performed. Those extracting solutions were also employed as mobile phases for the separation of the As species formed by size exclusion chromatography with inductively coupled plasma mass spectrometry (ICP-MS) as a selective As detector. Two main As containing species have been found in Brassica tissues (one of them at about 2 kDa and the other below 1.2 kDa). The first As species was found to be associated to thiol groups (monitoring 32S with double focusing ICP-MS). This can be ascribed to the presence of As-phytochelatin complexes. Electrospray-quadrupole-time of flight (ESI-Q-TOF) results indicated the presence of phytochelatins (apo-forms), the main metal bioligands in plants, which have also been shown to be induced by As. Oligomers of two, three and four sub-units, respectively (PC2, PC3 and PC4), with internal oxidation of the SH groups, have been extracted from Brassica leaves as well as a potential As–PC4 complex. These species have been further identified by collisional induced dissociation (CID).

Isothiocyanate release from soil-incorporated Brassica tissues

Isothiocyanates (ITCs) released from glucosinolates in Brassicaceous residues are thought to suppress soil-borne plant pests, however, little is known about ITC formation in soil. We conducted field and laboratory studies to determine the concentration and pattern of ITC production in soil following incorporation of rapeseed ( Brassica napus L.) and Indian mustard ( Brassica juncea Czern. & Coss). After tissue incorporation, ITC was extracted from soil with methanol, derivatised and quantified using HPLC. Maximum ITC concentrations near 1.0 nmol g −1 soil were measured immediately after tissue incorporation, with little production detected after 4 d. Only 1% or less of the ITC predicted from tissue glucosinolate concentrations was measured in soil amended with tissues of high glucosinolate rapeseed or mustard varieties. Tissue disruption at the cellular level afforded by freezing and thawing the tissues, resulted in maximum ITC concentrations ranging from 40 to 75 nmol ITC g −1 soil, thus increasing ITC release efficiencies to 14 and 26%. Our work indicates that soil-borne pest suppression is likely to be improved by choosing a high glucosinolate-containing variety of rapeseed or mustard and providing adequate moisture to increase ITC release and soil retention. However, the greatest improvements in the use of Brassica biofumigants to control soil-borne plant pests will be achieved by focussing on methods to increase cell disruption thereby maximising glucosinolate hydrolysis and ITC release.