Canola Seedlings Research Articles

Transcriptomic profiling of Brassica napus responses to Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic bacterial pathogen of plants. Unlike the well-characterized plant defense responses to highly adapted bacterial phytopathogens, little is known about plant response to P. aeruginosa infection. In this study, we examined the Brassica napus (canola) tissue-specific response to P. aeruginosa infection using RNA sequencing. Transcriptomic analysis of canola seedlings over a 5 day P. aeruginosa infection revealed that many molecular processes involved in plant innate immunity were up-regulated, whereas photosynthesis was down-regulated. Phytohormones control many vital biological processes within plants, including growth and development, senescence, seed setting, fruit ripening, and innate immunity. The three main phytohormones involved in plant innate immunity are salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). Many bacterial pathogens have evolved multiple strategies to manipulate these hormone responses in order to infect plants successfully. Interestingly, gene expression within all three phytohormone (SA, JA, and ET) signaling pathways was up-regulated in response to P. aeruginosa infection. This study identified a unique plant hormone response to the opportunistic bacterial pathogen P. aeruginosa infection.

ALLELOPATHIC EFFECT OF Sorghum bicolor AND Digitaria insularis ON GERMINATION AND INITIAL DEVELOPMENT OF CANOLA

Agriculture depends on biotic and abiotic factors, and one of them is allelopathy, defined as the chemical interference that one plant has on others, which can negatively affect germination. The objective of this work is to evaluate the allelopathic effects of Sorghum bicolor and Digitaria insularis on seed germination and initial development of canola seedlings (Brassica napus L.). A completely randomized design was used in a 2x5 factorial scheme (two extracts: D. insularis and S. bicolor) and five concentrations (0, 25, 50, 75, and 100%), with four replicates of fifty seeds, the plot being constituted by a 'gerbox' box containing 50 seeds evenly distributed. The variable analyzed were germination percentage (G), abnormal seedlings (AS), dead seeds (DS), length of the shoot (SL) and primary root (RL), total length (TL) of the seedling, shoot ratio (S/T), and root ratio (R/T). The aqueous extracts of D. insularis interfere in all variables studied, which compromises the formation of normal seedlings, regardless of concentration. The extract of S. bicolor expressed allelopathic effects only in concentrations above 75%. Both species can inhibit the initial development of canola plants.

Soil-Surface Straw Influences Micrometeorological Conditions Affecting Canola Mortality During Nighttime Frosts

Our objective was to measure alterations in the micrometeorological conditions surrounding canola seedlings during frost periods, and to quantify seedling mortality as a function of straw distribution on the ground surface. The data was acquired from 15 frosts in 2014. We used four treatments, comprising ground surface without straw (SWS), ground surface entirely straw-covered (SEC), sowing line without straw (SLW), and soil with preexisting surface straw (SES), over three experiments. Net radiation (NR), soil heat flux (G), air (Ta), leaf (Lf), rosette (Tr), and surface temperature (Ts), and plant mortality were evaluated. NR was higher in the SEC treatment and lower in the SLW treatment, whereas G was higher on straw-covered ground; Ts and Ta were lower in the SEC than in the other treatments during the most intense frosts. On 06/19, Tr in the SEC and SLW treatments was -0.66 °C and 0.42 °C, respectively; on 08/14, Lf was -3.62 °C and -2.88 °C in the SEC and SLW treatments, respectively. Plant mortality due to the frost on 06/19 was 30% in the SEC treatment, but 0% in the SLW treatment; the frost of 08/14 caused 33.8% mortality in the SEC treatment and 1.25% in the SLW treatment. This therefore showed that removing straw from the sowing line improved the microclimate around the plants, thus reducing canola mortality at the beginning of the growth cycle, which is when frost events most frequently occur.

Properties of root water transport in canola (Brassica napus) subjected to waterlogging at the seedling, flowering and podding growth stages

The objective was to clarify the role of root water transport in waterlogged canola plants. We examined the hypothesis that waterlogging triggers root suberization and lignification, which reduces the effectiveness of apoplastic bypass and increases the dependence of roots on the aquaporin-mediated water transport, and that this effect varies depending on the growth stage. Brassica napus plants at the seedling, flowering and podding growth stages were waterlogged for up to 8 days. Growth, gas exchange, leaf water potentials, and root hydraulic conductance were measured in addition to relative contributions of the aquaporin-mediated and apoplastic root water transport, gene expression levels of plasma membrane intrinsic proteins (BnPIPs), and lignin and suberin deposition in roots. Waterlogging decreased dry weights, gas exchange, leaf water potentials and root hydraulic conductivity more in plants at the seedling stage than other growth stages. It also accelerated root suberization and lignification resulting in an increase of a relative contribution of aquaporin-mediated water transport. The transcript levels of BnPIPs increased with an increasing duration of waterlogging. Effects on root water transport played an important role in the sensitivity of canola seedlings to waterlogging. Increased relative contribution of aquaporin-mediated water transport in waterlogged plants was accompanied by enhanced root suberization and lignification. The evidence points to the importance of maintaining functional aquaporins in plant survival of waterlogging.

Influence of Host Plant Species and Fertilization Regime on Larval Performance and Feeding Preference of the Redbacked Cutworm and the Pale Western Cutworm (Lepidoptera: Noctuidae).

The redbacked cutworm, Euxoa ochrogaster (Guenée), and the pale western cutworm, Agrotis orthogonia (Morrison), are generalist pests that cause sporadic economic damage to several annual crops in the Canadian Prairies. Early larval instars feed on foliage, whereas mature larvae eat into the stem and sever crop seedlings. Here, we evaluate the influence of annual crop species and host fertilization on the larval performance and feeding preference of both cutworm species. Performance is the ability of an insect to reach its maximum growth potential. The first set of experiments evaluated larval development and preference on canola (Brassica napus L. [Capparales: Brassicaeae]), field peas (Pisum sativa L. [Fabales: Fabaceae]), and spring wheat (Triticum aestivum L. [Cyperales: Poaceae]). The redbacked cutworm had higher performance on canola and peas, while the pale western cutworm had higher performance on wheat. In multiple-choice feeding experiments, the redbacked cutworm consumed more canola, whereas the pale western cutworm consumed more spring wheat. The third set of experiments evaluated larval development on fertilized and unfertilized seedlings of canola and spring wheat seedlings. When fed unfertilized seedlings, the redbacked cutworm had better performance on canola than spring wheat, whereas pale western cutworm had better performance on spring wheat than canola. Fertilizer application enhanced the performance of both cutworms regardless of the crop species. Despite their generalist feeding behavior, both cutworm species have a larval feeding preference for the host plant on which they achieve high performance. Canola-cereal cropping is a common crop rotation schedule in the region; however, this tactic will not negatively impact cutworm performance.

Assessment of Relative Potencies of Nitrogen Sources on Seedling Root Systems

Banding of N fertilizers below the seed is a common practice in direct seeded wheat dominated dryland agricultural systems, yet the placement of fertilizer below the seed has been shown to decrease yields and damage the root system architecture (RSA) in canola (Brassica napus). However, there is a lack of understanding as to which rates and sources of fertilizers might be safe for seedling root systems. The goal of this study was to compare the effect of three different N sources over a gradient of application rates on canola RSA. The effect of the fertilizer band on RSA has previously been imaged using rhizobox methods. However, the research presented here describes a novel technique for comparing sources and rates simultaneously while using the existing imaging technology. Canola seedlings were exposed to increasing rates of urea, ammonium sulfate (AS), and urea ammonium nitrate (UAN) from 0 mg N cm–1 to 40 mg N cm–1 placed 50 mm below the seed row. Canola showed significant changes in RSA as a result of the increasing ammoniacal‐N fertilizer rate. Dose response curves were developed for urea, AS, and UAN, and median lethal doses (LD50s) for tap roots were estimated at 4.7, 9.7, and 20.6 mg N cm–1, respectively. Comparisons between multiple measurements of the dose response curves revealed a consistent ranking of relative potencies among urea, AS, UAN (most to least toxic).Core Ideas New assay method for determining the relative potencies and safety ranges of different fertilizer sources as relates to roots system damage. Banded urea, ammonium sulfate, and urea ammonium nitrate N fertilizer sources all damage canola seedling root systems, but at differing rates. Dose response analysis was utilized to rank the relative potencies of ammoniacal‐N fertilizers from most toxic (urea) to least toxic (urea ammonium nitrate).

Enhancement of growth and salt tolerance in Brassica napus L. seedlings by halotolerant Rhizobium strains containing ACC-deaminase activity

A greenhouse experiment was conducted with four (ACC) deaminase-producing halotolerant Rhizobium strains, R29 (Sinorhizobium mellilote), R103 (Sinorhizobium mellilote), R281 (Rhizobium legominozaroum bv. phaseoli) and R307 (Rhizobium legominozaroum bv. phaseoli) and evaluated for their efficiency in improving canola plant growth under salt stress (with (50 mM NaCl + MgCl2) and control treatments), as factorial in randomized complete block design with three replications. Results revealed that with increasing salinity in compared to the negative control (0 mM salt), the overall reduction of growth of canola seedlings was around 21.3%. However, Rhizobium strains inoculation significantly increase the shoot/root elongation, shoot/root dry weight, stem diameter, leaf numbers, RWC up to 15.3/27.5, 24.86/53.1, 18.4, 18.05 and 8.4% respectively, compared to positive control (50 mM salt). Salt stress also caused 1.12-fold reduction in the root/shoot dry weight ratio compared to the absence of salt, while the salt tolerance index (ratio of biomass of salt stressed to non-stressed plant) was significantly increased (up to 1.26-fold) in inoculated plants compared to positive control. Furthermore, nutrient uptakes (N, P, K up to 56.14, 38.2 and 36.5%) under salt stress by canola was significantly (P < 0.01) increased. In summary, this study indicates that the use of ACC-deaminase producing halotolerant Rhizobium bacteria mitigates the salt stress effects.

Ameliorating Effect of Silicon on Growth Vigor, Physiological and biochemical Traits of Salinized Canola Seedlings (Brassica napus L.)

In the present study the ameliorating effects of Si nutrition supplied as 1 mmol L−1 sodium silicate were proved on the seedling growth of canola (Brassica napus L.) seedlings under salinity stress (i.e. 0, 30, 60, 90 and 120 mmol L−1sodium chloride). Salinity obviously disrupted cellular homeostasis, something was evident in the decreased percent of scavenging HO-free radical and Metal chelating %, and hence reduction in photosynthetic pigments contents (chl.a and carotenoids). Silicon nutrition, however, enabled canola cells to balance between the steady-state levels of different ROS through improving the detoxification of the excess ROS. This was prevalent in higher scavenging percent of HO- and metal chelating. In addition, Si maintained membranes integrity through improved levels of lipid peroxidation inhibition %. Si buffered oxidative stress through sustaining the enzymatic and non-enzymatic scavenging capacity of reactive oxygen species in salt-stressed plants. Enzymatic antioxidants such as (CAT, SOD, APX, and POS) activities as well as non-enzymatic antioxidants such as carotenoids contents phenolics contents increased at 120 mmol L−1 sodium chloride. Thus, silicon nutrition alleviated the deleterious effects of salinity on the growth of canola plants through increased reactive oxygen species scavenging capacity (enzymatically and non-enzymatically), maintaining the membrane integrity of seedling cells as evidenced by raising the reducing power contents, sustained higher levels of chlorophyll. Consequently, enhance seedlings growth observations.

Effects of Seed‐Placed Hog Manure‐Recovered Struvite on Canola Seedling Emergence

Core Ideas Struvite and coated monoammonium phosphate did not cause significant seedling toxicity regardless of rate. Monoammonium phosphate reduced canola seedling emergence in the clay loam at high P rate (15 mg kg−1). Final emergence count decreased in the order: struvite (88%) &gt; CMAP (86%) &gt; MAP (69%). Struvite can be applied at higher rates than monoammonium phosphate with minimal risk of seedling damage. Seedling toxicity is a major limitation to P fertilizer rates that can be seed‐placed with sensitive crops such as canola (Brassica napus L.). In this growth room bioassay, we tested whether struvite recovered from liquid hog (Sus domesticus L.) manure could improve seedling emergence in canola relative to monoammonium phosphate (MAP) and polymer‐coated monoammonium phosphate (CMAP). Twenty canola seeds per pot were planted in two low‐P soils (a Gleyed Regosolic sand [Entisol] and an Orthic Black Chernozemic clay loam [Udic Boroll]). The P sources were applied in the seedrow at rates of 7.5 or 15 mg P kg−1 soil (∼25 or 50 kg P2O5 ha−1), either at 5.4 or 10.9% seedbed utilization (SBU). Final emergence (percent of seeds planted), emergence rate, and lag were predicted using the Gompertz function. The higher rate of MAP reduced overall seedling emergence by 47% in the clay loam and 34% in the sand while the slow‐release P sources, struvite and CMAP, showed no significant evidence of seedling toxicity in either soil. Emergence was 0.6 d faster with struvite than with MAP, regardless of soil or P rate. Averaged across soils, SBUs, and P rates, final emergence decreased in the order: struvite (87%) &gt; CMAP (86%) &gt; MAP (69%), indicating the superiority of struvite and CMAP with respect to seedling toxicity. These results indicate that struvite can be seed‐placed at higher rates than those recommended for MAP on canola, with a much lower risk of seedling damage, thereby minimizing yield losses and replanting costs.

Genome-wide association study for electrolyte leakage in rapeseed/canola (Brassica napus L.)

Freezing temperature/frosts can cause significant damage to plants by rupturing plant cells. Rapeseed/canola (Brassica napus L.) is susceptible to freezing temperature at early seedling stage. The degree of cell rupture or seedling damage can be evaluated through the measurement of electrolyte leakage. Here, we measured the electrolyte leakage of a diversity panel of B. napus germplasm accessions under simulated freezing conditions. Preliminary data for electrolyte leakage measurement indicated that cold acclimation of two-week-old seedlings for 7 days at 4 °C followed by freezing treatment at − 12 °C for 2 h provided a reasonable diversity in response. With this protocol for electrolyte leakage, a genome-wide association study was conducted on 157 winter, semi-winter, and spring types of B. napus accessions that originated from 17 countries. A total of 37,454 single-nucleotide polymorphism (SNP) markers based upon genotyping-by-sequencing were used for the analysis. Ten QTL were identified as associated with electrolyte leakage of canola seedlings, which together explained 43% phenotypic variation. Five of the QTL were located on A-genome. We identified at least 33 orthologs of the functional candidate genes. Although no well-characterized cold regulatory genes were identified, there were some indications that genes involved in membrane structure, developmental processes, and extracellular transport may be involved in altering the electrolyte leakage following the short-term hard freeze and rapid defrosting suffered by the plants in our protocol.

Genome-wide association study for frost tolerance in canola (Brassica napus L.) under field conditions

Canola growers in the North Central Region of the United States and Canada are highly concerned about possible early frost. Plants can be killed due to their cells rupture when exposed to a freezing temperature. There are different methods to evaluate frost tolerance including field evaluation. Due to environmental variations, it is difficult to get an ideal condition for frost tolerance evaluation under field conditions. In this study, canola seedlings were grown in a greenhouse for 14 days at 20 °C and cold acclimated for 7–14 days at 4 °C. The acclimated seedlings were placed outside under field conditions based on predicted outside temperature between − 4 and − 8 °C to be exposed to a natural freezing condition. After an overnight freezing exposure, the seedlings were brought back to greenhouse to score the freezing induced seedling damage. The experiment was conducted in a randomized complete black design with two replications, and repeated the trial eight times. A genome-wide association study was conducted on 147 spring, winter, and semi-winter germplasm accessions obtained from 15 countries. A total of 37,111 single nucleotide polymorphism markers were used for the analysis. Three mixed populations with no growth type or geographic patterns were identified. One QTL that explained about 5% of the phenotypic variation and located on chromosome C04 was identified associated with frost tolerance of canola. Five potential genes related to frost tolerance and abiotic stress tolerance were identified.

Physiological studies and genome-wide microRNA profiling of cold-stressed Brassica napus

Temperature extremes, including cold, adversely impact plant growth and development. Plant responses to cold stress (CS) are regulated at both transcriptional and post-transcriptional levels. MicroRNAs (miRNAs), small non-coding RNAs, are known to be involved in post-transcriptional regulation of various developmental processes and metal stress in Brassica napus L. (canola), however, their role in response to CS is largely unknown. In this study, changes in various physiological parameters and endogenous abundance of miRNAs were characterized in spring canola seedlings (DH12075) exposed to 4 °C for 0–48 h. Cold stress induced electrolyte leakage, increased the levels of malondialdheyde and antioxidant enzymes and reduced photosynthetic efficiency. Using small RNA sequencing, 70 known and 126 novel miRNAs were identified in CS leaf tissues and among these, 25 known and 104 novel miRNAs were differentially expressed. Quantitative real-time (qRT) PCR analysis of eight selected miRNAs confirmed their CS responsiveness. Furthermore, the expression of six out of eight miRNAs exhibited an opposite trend in a winter variety of canola, ‘Mendel’, when compared to ‘DH12075’. This first study on the B. napus miRNAome provides a framework for further functional analysis of these miRNAs and their targets in response to CS which may contribute towards the future development of cold resilient crops.

Potential biopesticides for crucifer flea beetle, Phyllotreta cruciferae (Coleoptera: Chrysomelidae) management under dryland canola production in Montana

The crucifer flea beetle, Phyllotreta cruciferae (Goeze), is an economically important and dominant pest of canola (Brassica napus L) in the Northern Great Plains of the USA. The current flea beetle management strategy is based on using synthetic chemical treated seeds and if necessary, foliar spray of chemicals at canola seedlings in early spring for targeting adult population. However, there is an increasing demand for development of alternative management strategies for P. cruciferae pertaining to concerns over the development of resistance to synthetic insecticides and non-target effects on pollinators and other beneficial insects. Replicated field trials were conducted to test the efficacy of several commercially available biopesticides including Entrust® (spinosad), entomopathogenic nematode Steinernema feltiae + Barricade® (polymer gel 1%), Aza-Direct® (azadirachtin), Pyganic 1.4® EC (pyrethrin), Grandevo® SC (Chromobacterium subtsugae), Venerate® XC (Heat killed Burkholderia sp. strain A396 as seed treatment and foliar application) and Gaucho® (imidacloprid) (chemical check) for the P. cruciferae management at two locations (Conrad and Sweetgrass) of Montana in 2016. Biopesticide products were evaluated based on canola leaf area injury ratings and seed yield levels. Although, there was no clear trend of canola yield increase, selected biopesticide treatments were effective in maintaining low leaf area injury ratings as compared to untreated control. Entrust was able to maintain low leaf area injury ratings (8.5–14.5%) when compared to untreated control (16.0–21.4%) at both the locations. Entomopathogenic nematodes, Steinernema feltiae + Barricade® and Venerate® applied as foliar treatments maintained significantly lower feeding injury pressure at Sweetgrass (11.8%) and Conrad (13.4%) locations respectively, when compared to the untreated control. Our study results suggest that these biopesticide treatment results were comparable in efficacy to the chemical seed treatment Gaucho®. Other two biopesticide products- Aza-Direct® and Pyganic 1.4® EC treatments did not provide effective control of P. cruciferae at both the locations.

The role of calcium, silicon and salicylic acid treatment in protection of canola plants against boron toxicity stress

Boron (B) toxicity often limits crop yield and the quality of production in agricultural areas. Here, we investigated the effects of calcium (Ca), silicon (Si) and salicylic acid (SA) on development of B toxicity, B allocation in canola (Brassica napus cultivar Sarw 4) and its role in non-enzymatic antioxidants in relation to yield of this cultivar under B toxicity. Canola seedlings were subjected to four B levels induced by boric acid in the absence or presence of Ca, Si and SA. The results showed that Ca, Si and SA addition ameliorated the inhibition in canola growth, water content (WC), and improved siliqua number, siliqua weight and seed index. The B content in shoots and roots and total B accumulation in the whole plant were increased in control plants under B-toxicity-stress, and these parameters were significantly decreased by addition of Ca, Si and SA. The shoot ascorbate pool (ascorbate, AsA, and dehydroascorbate, DHA), α-tocopherol and phenolics (free and bound) were increased under B toxicity, and were significantly decreased in most cases by addition of Ca, Si and SA, except α-tocopherol, which increased at low B levels (0, 25 and 50mg kg soil-1). The glutathione content did not obviously change by B stress, while added Ca, Si and SA inhibited its accumulation under B stress. In addition, B toxicity reduced the shoot flavonoids content; however, this reduction was not alleviated by the use of Ca, Si and SA treatments. It could be concluded that growth and yield of canola plants grown under high B concentration improved after external application of Ca, Si or SA.

A bioplastic-based seed coating improves seedling growth and reduces production of coated seed dust

ABSTRACTAlthough recently introduced, film-coating of agronomic seeds is now widely accepted in modern agriculture as an effective technology for protecting germinating seeds and seedlings. These experiments explored the possibility of using a bioplastic-based formulation to film-coat corn (maize; Zea mays L.) and canola (Brassica napus L.) seeds, alone and in combination with synthetic pesticides and plant growth-promoting bacteria. The thin bioplastic coat did not affect percent germination or seedling growth. However, incorporating spores of the plant growth-promoting bacterium Bacillus subtilis QST 713 into the bioplastic matrix resulted in a greater elongation of corn and canola seedlings than that of seedlings from untreated seeds. Specifically, stems and roots of seedlings that germinated from corn seeds coated with bioplastic containing spores were 18.0% and 21.4% longer, respectively, than stems and roots from uncoated control seeds. In canola seeds, these values were 19.9% and 20.9% higher for stem and roots, respectively. Incorporating a neonicotinoid insecticide, imidacloprid, and a fungicide, pyraclostrobin, into bioplastic coatings, along with B. subtilis spores, provided results comparable to spores and bioplastic alone. Coated seeds were also evaluated for their potential to generate dust after abrasion testing, using a novel image-based method made possible because seed coatings are typically artificially colored. Abraded seed coat fragments are consequently easily detectable with conventional optical instruments. Corn and canola seeds coated with bioplastic released up to 86.1% and 97.6% less dust during abrasive handling than seeds coated with a commercial seed coating matrix measured by the optical approach described here.

Exogenous application of poly-γ-glutamic acid enhances stress defense in Brassica napus L. seedlings by inducing cross-talks between Ca2+, H2O2, brassinolide, and jasmonic acid in leaves

Poly-γ-glutamic acid (γ-PGA) is a microbe-secreted isopeptide shown to promote growth and enhance crop stress tolerance. However, its downstream signaling pathways are unknown. Here, we studied γ-PGA-induced tolerance to salt and cold stresses. Pretreatment with γ-PGA contributed to enhance stress tolerance of canola seedlings by promoting proline accumulation and total antioxidant capacity (T-AOC) improvement. Further, Ca2+, H2O2, brassinolide, and jasmonic acid were found to be involved in the γ-PGA-induced process. First, using signal blockers, we concluded that γ-PGA activated Ca2+ fluctuations in canola seedling leaves. Second, the activated Ca2+ further elicited H2O2 production by Ca2+-binding proteins CBL9, CPK4, and CPK5. Third, the H2O2 signal promoted brassinolide and jasmonic acid biosynthesis by upregulating key genes (DWF4 and LOX2, respectively) for synthesizing these compounds. Lastly, brassinolide and jasmonic acid increased H2O2 which promoted proline accumulation and T-AOC improvement and further enhanced Ca2+-binding proteins including CaM, CBL10, and CPK9.

Effects of rate and application method on the efficacy of metam sodium to reduce clubroot (Plasmodiophora brassicae) of canola

Clubroot, caused by Plasmodiophora brassicae, has become a serious threat to canola (Brassica napus) production in western Canada. Experiments were conducted to evaluate the effect of rate of metam sodium fumigant (dithiocarbamate; sodium N-methyldithiocarbamate; trade name Vapam) and application methods including watering, soil surface covering, and soil incorporation on clubroot of canola. At higher rates (0.4–1.6 mL−1 L soil) metam sodium increased canola seedling emergence and plant health, and reduced root hair infection, gall weight and clubroot severity under greenhouse conditions. Metam sodium application improved subsequent plant growth and reduced clubroot severity, but land preparation and volume of water applied did not affect efficacy. The incorporation of metam sodium into the soil and plastic covering after application improved fumigant efficacy. The study showed that soil fumigation with metam sodium can reduce clubroot severity and improve plant health in the subsequent canola crop.

Effects of triacontanol on ascorbate-glutathione cycle in Brassica napus L. exposed to cadmium-induced oxidative stress

The ability of exogenous triacontanol (TRIA), a plant growth regulator, to reduce Cd toxicity was studied in canola (Brassica napus L.) plants. The following biological parameters were examined in canola seedlings to investigate TRIA-induced tolerance to Cd toxicity: seedling growth, chlorophyll damage and antioxidant response. In particular, TRIA application reduced Cd-induced oxidative damage, as shown by reduction of ROS content, lipoxygenase (LOX) activity and lipid peroxidation level. TRIA pretreatment increased non-enzymatic antioxidant contents (ascorbate, AsA, glutathione and GSH), phytochelatin content (PCs) and activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), monodehydroascorbate reductase (MDHAR), dehydro ascorbate reductase (DHAR), and glutathione reductase (GR), so reducing the oxidative stress. These results clearly indicate the protective ability of TRIA to modulate the redox status through the antioxidant pathway AGC and GSH, so reducing Cd-induced oxidative stress.

Enhanced tolerance to salt stress in canola (Brassica napus L.) seedlings inoculated with the halotolerant Enterobacter cloacae HSNJ4

Using halotolerant plant growth-promoting rhizobacteria (PGPR) to alleviate damages caused by salt stress is an effective method in agriculture. In the present study, an Enterobacter cloacae strain (HSNJ4) that was isolated from the rhizosphere of saline soil was found to be the most effective for promoting canola seed germination among eight halotolerant bacteria tested. Then, the effects of HSNJ4 inoculation on the growth and physiological responses of canola seedlings were investigated under three different levels of salt stress in a pot experiment. The root length, shoot length, amount of lateral roots, and chlorophyll content in HSNJ4-inoculated canola seedlings increased significantly under salt stress. Physiological analysis showed that malondialdehyde content was decreased, whereas proline content and antioxidant enzyme activity were increased by HSNJ4 inoculation at NaCl concentrations of 50 and 100mM. Moreover, HSNJ4 inoculation effectively increased endogenous indole-3-acetic acid (IAA) content and reduced ethylene emission under simulated salt stress conditions. Cultures of HSNJ4 demonstrated that under conditions of salt stress, HSNJ4 could indeed produce both IAA and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Hence, it is plausible that HSNJ4 balances the relative content of IAA and ethylene in canola seedlings to enhance their salt tolerance.

Plant growth promotion and nitrogen fixation in canola (Brassica napus) by an endophytic strain of Paenibacillus polymyxa and its GFP-tagged derivative in a long-term study

Paenibacillus polymyxa P2b-2R is an endophytic strain capable of fixing nitrogen (N) and promoting growth in a broad range of hosts. In this study, the ability of Paenibacillus polymyxa P2b-2R to fix N and promote the growth of canola (Brassica napus L.) was determined in a 3-month-long trial. We also compared growth promoting and N-fixing capability of wild-type P2b-2R and its GFP-tagged counterpart. Canola seedlings were inoculated with strain P2b-2Rgfp or P2b-2R. Non-inoculated seedlings were used as controls. Canola seedlings were grown for 3 months before evaluating plant growth promotion (length, biomass, and pod mass) and N fixation (using foliar 15N dilution assay). P2b-2Rgfp inoculation significantly promoted canola growth by increasing seedling length by 2-fold, biomass by 2.5-fold, and fixing 35% of its foliar N, respectively. P2b-2R inoculation also increased seedling length by 70%, biomass by 2-fold, and fixed 27% of N. Seedling biomass and length, and the amount of N fixed by P2b-2Rgfp-treated seedlings was significantly greater than the P2b-2R-treated seedlings. P2b-2R or P2b-2Rgfp inoculation also lead to an increase of pod mass (more than 50%), indicating that these strains might play a role in enhancing the yield of canola by acting as biofertilizer.