Soil boron and selenium removal by three plant species

High concentrations of boron (B) and selenium (Se) naturally found in the environment are detrimental to sustainable agriculture in the western USA. Greenhouse pot experiments were conducted to study B and Se uptake in three different plant species; Brassica juncea (L.) Czern (wild brown mustard), Festuca arundinacea Schreb. L. (tall fescue), and Brassica napus (canola) were grown in soil containing naturally occurring concentrations of 3.00 mg extractable B kg^–1 and 1.17 mg total Se kg^–1 soil. During the growing season, four intermediate harvests were performed on wild mustard and tall fescue. Final harvest I consisted of harvesting wild mustard, canola, and clipping tall fescue. Final harvest II consisted of harvesting wild mustard, which had been planted in soil in which wild mustard was previously grown, and harvesting previously clipped tall fescue. The greatest total amount of above ground biomass and below surface biomass was produced by tall fescue. Plants were separated into shoots and roots, weighted, and plant tissues were analyzed for total B and Se. The highest concentrations of tissue B were recovered in shoots of wild mustard and canola at final harvest I, while roots from tall fescue contained the highest concentrations of B irrespective of the harvest. Tissue Se concentrations were similar in all plants species. Soils were analyzed for residual B and Se. Extractable soil B concentrations at harvest times were lowered no less than 32% and total Se no less than 24% for all three species. The planting of wild mustard, canola, or tall fescue can reduce water-extractable B and total Se in the soil.     

Root, shoot tissues of Brassica juncea and Cereal secale promote potato health

Brassica species are increasingly being used as cover crops to suppress soil-borne diseases in potato cropping systems. Experiments were conducted in controlled environments and in the field to evaluate the effects of cover crop root or shoot or a combination of root and shoot tissues on potato root and tuber health. In a lab assay we examined the extent to which volatile compounds released from tissues of two cover crop species, rye (Cereale secale L.) and oriental mustard (Brassica juncea L.), could inhibit mycelium growth of two important potato diseases, Rhizoctonia solani and Pythium ultimum. Twenty-four hours into the lab assay, volatile compounds from all residues suppressed fungal growth. After 48 h, marked suppression of hyphal growth continued in the presence of mustard residues but not in the presence of rye tissues or the control without tissues. A 75 L volume container experiment evaluated the effect of incorporating different quantities of mustard shoot and root tissues (none, comparable to field level and fourfold field level) into R. solani and P. ultimum infested soil on potato growth, root health and tuber disease. In the container study, incorporating mustard shoots at the highest dose increased potato yield by 54% and reduced disease rating to 2.3 compared to a severe rating of 4.4 in the control. In the field trial, potato growth, root health and tuber disease levels were evaluated in plots where disease management involved either incorporation of mustard or rye cover crop roots, shoots and whole plants (roots plus shoots) or standard farmer practice of a fumigated fallow as a control. White root tissue was used as a health indicator, and averaged 58 and 78% in the fumigated control and mustard cover crop treatments, respectively. The highest healthy root tissue status (91%) was recorded where whole plants of mustard were incorporated. In contrast to the visual assessment of root and tuber health, tuber yield in the field was not influenced by cover crop treatment. Across experiments, the incorporation of or exposure to whole mustard plants was consistently effective at suppressing soil-borne fungi and promoting healthy roots and tubers, especially at higher rates of biomass. Mustard should be managed so as to maximize incorporated biomass for effective biofumigation. Multipurpose management requiring removal of mustard shoots is incompatible with promoting potato rhizosphere health.     

Transformation of Brassica napus canola cultivars with Arabidopsis thaliana acetohydroxyacid synthase genes and analysis of herbicide resistance

Summary A survey of selected crop species and weeds was conducted to evaluate the inhibition of the enzyme acetohydroxyacid synthase (AHAS) and seedling growth in vitro by the sulfonylurea herbicides chlorsulfuron, DPX A7881, DPX L5300, DPX M6316 and the imidazolinone herbicides AC243,997, AC263,499, AC252,214. Particular attention was given to the Brassica species including canola cultivars and cruciferous weeds such as B. kaber (wild mustard) and Thlaspi arvense (stinkweed). Transgenic lines of B. napus cultivars Westar and Profit, which express the Arabidopsis thaliana wild-type AHAS gene or the mutant gene csr1-1 at levels similar to the resident AHAS genes, were generated and compared. The mutant gene was essential for resistance to the sulfonylurea chlorsulfuron but not to DPX A7881, which appeared to be tolerated by certain Brassica species. Cross-resistance to the imidazolinones did not occur. The level of resistance to chlorsulfuron in transgenic canola greatly exceeded the levels that were toxic to the Brassica species or cruciferous weeds. Direct selection of transgenic lines with chlorsulfuron sprayed at field levels under greenhouse conditions was achieved.     

Gene transfer between canola (Brassica napus L. and B. campestris L.) and related weed species

Brassica species are particularly receptive to gene transformation techniques. There now exists canola genotypes with transgenic herbicide resistance for glyphosate, imidazolinone, sulfonylurea and glufosinate herbicides. The main concern of introducing such herbicide resistance into commercial agriculture is the introgression of the engineered gene to related weed species. The potential of gene transfer between canola (Brassica napus and B. campestris) and related weed species was determined by hand pollination under controlled greenhouse conditions. Canola was used as both male and female parent in crosses to the related weed species collected in the Inland Northwest region of the United States. Weed species used included: field mustard (B. rapa), wild mustard (S. arvensis) and black mustard (B. nigra). Biological and cytological aspects necessary for successful hybrid seed production were investigated including: pollen germination on the stigma; pollen tube growth down the style; attraction of pollen tubes to the ovule; ovule fertilisation; embryo and endosperm developmental stages. Pollen germination was observed in all 25 hybrid combinations. Pollen tubes were found in the ovary of over 80% of combinations. About 30% of the hybrid combinations developed to the heart stage of embryo development or further. In an additional study involving transgenic glufosinate herbicide resistant B. napus and field mustard it was found that hybrids occurred with relatively high frequency, hybrids exhibited glufosinate herbicide resistance and a small proportion of hybrids produced self fertile seeds. These fertile plants were found to backcross to either canola or weed parent.     

Assessment of glucosinolate-derived isothiocyanates as potential natural antifungal compounds against citrus sour rot disease agent Geotrichum citri-aurantii

In this study, the antifungal effects of six different isothiocyanate (ITCs) compounds (methyl, allyl, butyl, ethyl, benzyl and 2-phenylethyl ITCs) were investigated to be use against the citrus sour rot disease caused by Geotrichum citri-aurantii in vitro and semi-commercial (in vivo) conditions. Antifungal activities of the vapour phases of different ITC compounds were examined on the arthroconidia germination and mycelial growth of G. citri-aurantii. Mycelial growth of G. citri-aurantii was inhibited in a concentration-dependent way. The minimum inhibitory concentrations of benzyl, methyl, allyl and ethyl ITCs on mycelial growth were 0.06, 0.08, 0.10 and 0.10 µl/L, respectively. Arthroconidia germination of G. citri-aurantii was completely inhibited by benzyl, methyl, allyl and ethyl ITCs at concentrations of 0.05, 0.07, 0.07 and 0.07 µl/L, respectively. Light microscopy observations revealed that the ITC compounds, at completely inhibiting concentrations, caused considerable morphological changes in the fungal hyphae. Under in vivo conditions, the average rotting area caused by G. citri-arantii was inhibited 100% by ethyl, methyl and allyl ITC compounds at concentrations of 8.0, 12.0 and 12.0 µl/L, respectively. Results suggest that ITC’s may be useful and effective natural antifungal compounds to control the citrus sour rot disease agent.     

Comparison of tolerance of <Emphasis Type="Italic">Brassica juncea</Emphasis> and <Emphasis Type="Italic">Vigna radiata</Emphasis> to cadmium

The effect of different cadmium concentrations (6–120 μM) on Hill reaction activity (HRA) of isolated chloroplasts, contents of chlorophylls (Chls) and carotenoids (Cars), and Cd uptake and accumulation in plant organs of Indian mustard (Brassica juncea L. cv. Vitasso) and mung bean [Vigna radiata (L.) Wilczek] were determined. The Cd stress inhibited photochemical activity of isolated chloroplasts of both species and in both tested developmental stages. On the basis of EC₅₀ values, the mung bean showed a higher sensitivity to Cd treatment than Indian mustard. The higher sensitivity of both species was determined in the earlier than in the older developmental stage. The leaves of Cd-treated plants possessed lower contents of Chls and Cars in both species and the negative effect increased with Cd concentration. A difference between species was also found in Cd uptake and accumulation. In both species, Cd was accumulated more in roots than in shoots, with higher accumulation in Indian mustard than in mung bean.     

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.     

Hyperaccumulation of Lead by Roots, Hypocotyls, and Shoots of Brassica juncea

The effects of different concentrations of lead nitrate (10^–5 to 10^–3 M) on root, hypocotyl, and shoot growth of Indian mustard (Brassica juncea L. var. megarrhiza), and the uptake and accumulation of Pb²⁺ by its roots, hypocotyls, and shoots were investigated. Lead had no significant inhibitory effect on the root growth at concentrations of 10^–5 to 10^–4 M during the entire treatment, while at 10^–3 M, Pb slightly inhibited the root and shoot growth. B. juncea has ability to take up Pb from solutions and accumulate it in its roots, and transport and concentrate it. The Pb contents in the parts of plants treated with 10^–3 M Pb were greater than those of untreated plants, by factors of 230 in the roots, 170 in the hypocotyls, and 3 in the shoots.     

Effects of aluminium on canola roots

There is little information on the effects of aluminium (Al) on canola (Brassica napus var. napus L.), which is a commercially important crop species in many parts of the world. In this report, we describe the effects of Al on roots of canola seedlings grown hydroponically in a nutrient solution at pH 4.5. The morphological and ultrastructural changes that accompanied these growth effects were examined. Additions to the nutrient solution of Al at concentrations below 40 μM stimulated root growth of canola seedlings, increasing both the size and number of central cap cells. The stimulation of root growth did not appear to be due to the alleviation of a proton toxicity at the root surface. At concentrations of Al above 60 μM, root growth was strongly inhibited, with cellular damage being observed primarily in peripheral root cap cells. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phytoextraction of selenium from soils irrigated with selenium-laden effluent

This two-part study compared the efficacy of different plant species to extract Se from soils irrigated with Se-laden effluent. The species used were: Brassica napus L. (canola), Brassica juncea Czern L. and Coss (Indian mustard), and Hordeum vulgare L. (barley). In Study 1 we irrigated the plants with a saline effluent containing 0.150 mg Se L^–1, while in Study 2, the same species were planted in a saline soil selenized with 2 mg Se L^–1. Plants were simultaneously harvested 120 days after planting. In Study 1, there were only slight effects of treatment on dry matter (DM) yield. Plant Se concentrations averaged 21 g Se g^–1DM for the Brassica species, and 4.0 g Se g^–1 DM for barley. Total Se added to soils via effluent decreased by 40% for Brassica species and by 20% for barley. In Study 2, total DM decreased for all species grown in saline soils containing Se. Plant Se concentrations averaged 75 g g^–1 DM for Brassica species and 12 g Se g^–1 DM for barley. Total Se added to soils prior to planting decreased by 40% for Brassica species and up to 12% for barley. In both studies, plant accumulation of Se accounted for at least 50% of the Se removed in soils planted to Brassica and up to 20% in soils planted to barley. Results show that although the tested Brassica species led to a significant reduction in Se added to soil via use of Se-laden effluent, additional plantings are necessary to further decrease Se content in the soil.     

Hydrolysis products of glucosinolates in Brassica napus tissues as inhibitors of seed germination

Enzymatic hydrolysis of glucosinolates, a class of compounds found in Brassica species, results in a number of products with potential to inhibit seed germination. To investigate the impact of both volatile and water-soluble allelochemicals, germination bioassays using Lactuca sativa seeds were conducted with root and combined leaf and stem tissues of Brassica napus. Tissues in which glucosinolates were hydrolyzed to remove volatile glucosinolate degradation products were compared with intact tissues and water controls. Only tissues containing glucosinolates produced volatiles that inhibited germination. Volatiles were trapped and identified using GC-MS. Volatiles produced in greater quanitity from intact tissues than from tissues without glucosinolates were almost exclusively glucosinolate hydrolysis products. Water-soluble components also inhibited germination. Chemical analysis of extracts confirmed the presence of glucosinolate hydrolysis products, but indicated the involvement of additional allelochemicals, especially in leaf and stem tissues. Results support the proposal that glucosinolate-containing plant tissues may contribute to reductions in synthetic pesticide use if weed seeds are targeted.Abbreviations ITC isothiocyanates - CN organic cyanides - OZT oxazolidinethione - iRoot intact root tissue - iL&S intact leaf and stem tissue - hRoot hydrolyzed root tissue - hL&S hydrolyzed leaf and stem tissue     

Allelopathic effect of <Emphasis Type="Italic">Nepeta meyeri</Emphasis> Benth. extracts on seed germination and seedling growth of some crop plants

In order to evaluate the allelopathic potential of Nepeta meyeri Benth., the effects of aqueous extracts (0.125, 0.25, 0.5, 1, 2.5 and 5%) prepared from roots and leaves of N. meyeri were studied on the seed germination and seedling growth of several economically important crops (barley, wheat, canola, safflower, and sunflower). Both the root and leaf extracts of N. meyeri caused a general phytotoxic effect on the seed germination and seedling growth of barley and sunflower at all concentrations. However, both the root and leaf extracts significantly increased the seedling growth of wheat, especially at the lower concentrations 0.125, 0.25 and 0.5%, whereas the higher concentrations had a neutral effect. The seed germination and the seedling growth of canola and safflower were also generally improved by both extracts, especially at lower concentrations. However, these advantages were not observed at higher concentrations, at which the extracts mostly had a phytotoxic effect on canola and safflower. The Allelopathic activity of N. meyeri depended on whether the extract was derived from the leaf or root parts of the plant. The maximum allelopathic effect occurred with leaf extracts. The results demonstrate that the aqueous extracts from N. meyeri have allelopathic potential and should be evaluated as an allelopathic species, presenting a risk or advantage to seed germination and seedling growth of crop or weed plants.     

ALLYL ISOTHIOCYANATE RELEASE AND THE ALLELOPATHIC POTENTIAL OF BRASSICA NAPUS (BRASSICACEAE)

The allelopathic potential of Brassica species has been attributed to release of the mustard oil glycosides which they produce in large quantities. Upon hydrolysis, these glucosinolates yield isothiocyanates, compounds with strong antibiotic properties. The objective of this study was to assess whether Brassica napus, a common and widespread crop and weed crucifer, is capable of allelopathic interference, and if so, whether its glycoside derivative, allyl isothiocyanate (AI), is capable of producing this interference. Wild type and low glucosinolate-mutant B. napus were grown in low organic content soil under greenhouse conditions, and AI release into soil was monitored. Most plants released low levels of AI, though approximately 10% released much higher levels. Wild type plants released more AI than mutants. Growth of the target species, Medicago sativa, was not affected by additions of AI to soils at concentrations equal to the median and 95% quantile from the B. napus soils. In replacement series experiments, the two B. napus genotypes suppressed growth of M. sativa equally despite differences in AI release rate. In an intraspecific replacement series experiment, the two B. napus genotypes were equal competitors. Under our experimental conditions, B. napus showed no indication of being allelopathic, and AI concentrations typical of soils around B. napus plants did not inhibit target plants.     

Turgor Maintenance by Osmoregulation inBrassica napusandB. junceaunder Field Conditions

Indian mustard (Brassica juncea(L) Czernjacw) maintains higherleaf turgor than canola (B. napusL.) under water deficits andthis is related to the greater yield of mustard under theseconditions. The work reported in this paper was designed tostudy the way mustard maintains this turgor advantage. It wasbased on three field experiments that each used at least twocultivars or lines of each species. The leaf water potentialat which leaves reached zero turgor was consistently lower inmustard than in canola (up to 1.1 MPa lower). This differencearose from a greater rate of decline in leaf osmotic potentialwith declining water potential in mustard rather than from anydifference in the osmotic potential at full turgor. Calculationsof solute accumulation showed that mustard had a greater capacityto osmoregulate than canola, with this capacity being the basisfor its advantage in turgor maintenance. Other differences inplant water relations were consistent with the differences inosmoregulation, with the predicted relative water content ofleaves at an osmotic potential of -2.5 MPa being 0.43 for canolaand 0.61 for mustard. Mustard's greater capacity to accumulatesolutes is concluded to be a major factor in its greater yieldunder water deficits. Brassica napusL.; Brassica juncea(L) Czernjacw; Indian mustard; canola; water deficit; plant water relations; osmoregulation; osmotic adjustment; turgor     

Uptake and accumulation of lead by roots,hypocotyls and shoots of Indian mustard [Brassica juncea (L.)]

The effects of different concentrations of lead nitrate on root, hypocotyl and shoot growth of Indian mustard (Brassica juncea var. Megarrhiza), and the uptake and accumulation of Pb²⁺ by its roots, hypocotyls and shoots were investigated in the present study. The concentrations of lead nitrate (Pb(NO₃)₂) used were in the range of 10⁻⁵–10⁻³ M. Root growth decreased progressively with increasing concentration of Pb²⁺ in solutions. The seedlings exposed to 10⁻³ M Pb exhibited substantial growth reduction and produced chlorosis. Brassica juncea has considerable ability to remove Pb from solutions and accumulate it. The Pb content in roots of B. juncea increased with increasing solution concentration of Pb²⁺. The amount of Pb in roots of plants treated with 10⁻⁴, 10⁻³ and 10⁻⁵ M Pb²⁺ were 184-, 37- and 6-fold, respectively, greater than that of roots of the control plant. However, the plants transported and concentrated only a small amount of Pb in their hypocotyls and shoots, except for the group treated with 10⁻³ M Pb²⁺.     

Plant growth-promoting bacteria that decrease heavy metal toxicity in plants

Kluyvera ascorbata SUD165 and a siderophore-overproducing mutant of this bacterium, K. ascorbata SUD165/26, were used to inoculate tomato, canola, and Indian mustard seeds which were then grown in soil for 25-42 days in the presence of either nickel, lead, or zinc. The parameters that were monitored included plant wet and dry weight, protein and chlorophyll content in the plant leaves, and concentration of heavy metal in the plant roots and shoots. As indicated by a decrease in the measured values of these parameters, in all instances, plant growth was inhibited by the presence of the added metal. Both bacterial strains were effective, although not always to a statistically significant extent, at relieving a portion of the growth inhibition caused by the metals. In most cases, the siderophore overproducing mutant K. ascorbata 165/26 exerted a more pronounced effect on plant growth than did the wild-type bacterium K. ascorbata SUD165. The data suggest that the ability of these bacteria to protect plants against the inhibitory effects of high concentrations of nickel, lead, and zinc is related to the bacteria providing the plants with sufficient iron.     

Control of the take-all fungus byMicrodochium bolleyi,and interactions involvingM. bolleyi,Phialophora graminicola andPericonia macrospinosa on cereal roots

Summary In glasshouse experiments,Microdochium bolleyi (Mb) significantly reduced infection of wheat roots by the take-all fungus,Gaeumannomyces graminis vartritici (Ggt), when inocula were dispersed in soil at ratios of 10∶1 (Mb:Ggt) or more. Spread of take-all lesions up roots from a layer of inoculum also was reduced when Mb was inoculated immediately below the crown. In contrast,Periconia macrospinosa did not control take-all even at an inoculum ratio of 100∶1. M. bolleyi interfered with growth on roots byPhialophora graminicola, a known biocontrol agent of take-all. It is suggested that this phenomenon and control of take-all by these fungi occur by competition for cortical cells that senesce in the normal course of root development.     

On-line detection of root-induced volatiles in Brassica nigra plants infested with Delia radicum L. root fly larvae

Plants emit various volatile organic compounds (VOCs) upon herbivore attack. These VOC emissions often show temporal dynamics which may influence the behavior of natural enemies using these volatiles as cues. This study analyzes on-line VOC emissions by roots of Brassica nigra plants under attack by cabbage root fly larvae, Delia radicum. Root emitted VOCs were detected using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and Gas Chromatography–Mass Spectrometry (GC–MS). These analyses showed that several sulfur containing compounds, such as methanethiol, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS) and glucosinolate breakdown products, such as thiocyanates (TC) and isothiocyanates (ITC), were emitted by the roots in response to infestation. The emissions were subdivided into early responses, emerging within 1–6 h after infestation, and late responses, evolving only after 6–12 h. The marker for rapid responses was detected at m/z 60. The ion detected at m/z 60 was identified as thiocyanic acid, which is also a prominent fragment in some TC or ITC spectra. The emission of m/z 60 stopped when the larvae had pupated, which makes it an excellent indicator for actively feeding larvae. Methanethiol, DMS and DMDS levels increased much later in infested roots, indicating that activation of enzymes or genes involved in the production of these compounds may be required. Earlier studies have shown that both early and late responses can play a role in tritrophic interactions associated with Brassica species. Moreover, the identification of these root induced responses will help to design non-invasive analytical procedures to assess root infestations.     

Putrescine Effect on Nitrate Reductase Activity, Organic Nitrogen, Protein, and Growth in Heavy Metal and Salinity Stressed Mustard Seedlings

Putrescine effect on nitrate reductase activity, organic nitrogen and protein contents, and plant growth under Cd or Pb (0.1 – 2 mM) and salinity (5 and 100 mM NaCl) stresses was examined in Indian mustard (Brassica juncea L. cv. RH-30) seedlings. Cd or Pb and salinity inhibited nitrate reductase activity and decreased organic nitrogen and protein contents in leaf tissue. The increased nitrate reductase activity induced by putrescine was correlated with increased organic nitrogen and protein contents and growth of plants.     

Secondary metabolites produced by a root‐inhabiting sterile fungus antagonistic towards pathogenic fungi

Aims: A sterile red fungus (SRF) isolated from cortices of roots of both wheat (Triticum aestivum cv. Gamenya) and ryegrass (Lolium rigidum cv. Wimmera) was found to protect the hosts from phytopathogens and promote plant growth. In this work, the major secondary metabolites produced by this SRF were analysed, and their antibiotic and plant‐growth‐promoting activities investigated. Methods and Results: Two main compounds, veratryl alcohol (VA) and 4‐(hydroxymethyl)‐quinoline, were isolated from the culture filtrate of the fungus. In antifungal assays, VA inhibited the growth of Sclerotinia sclerotiorum and Pythium irregulare even at low amounts, while high concentrations (>100 μg per plug) of 4‐(hydroxymethyl)‐quinoline were needed. Both metabolites revealed weak inhibition of Rhizoctonia solani. Furthermore, both compounds showed a growth promotion activity on canola (Brassica napus) seedlings used as bioassays. Conclusions: Isolation and characterization of the main secondary metabolites from culture filtrates of a root‐inhabiting sterile fungus are reported. The biological assays indicate that these secondary metabolites may have a role in both plant growth regulation and antifungal activity. Significance and Impact of the Study: This study provides a better understanding of the metabolism of a cortical fungus that may have a useful role in the biological suppression of root‐infecting soil‐borne plant pathogens.