Isolation of novel plant-beneficial soil bacteria to enhance legume crop productivity

Non-Peer ReviewedPlant roots support the growth of a variety of soil microorganisms that have beneficial or detrimental effects on plant growth. As producers move to earlier seeding into cool wet soils, problems with pea and lentil seedling decay (damping off) and root rot are increasing. Attempts to control Pythium and Fusarium spp. with seed coatings containing the fungicides Captan or Thiram are being used however, the activity of these compounds is limited to approximately 2-3 weeks after planting. The objective of this project is to isolate microorganisms with the ability to be competitive in the rhizosphere of plants and biologically control root diseases of legumes. Over six hundred isolates were obtained from the rhizosphere of chickpea, lentil and pea from commercial farms in Rosetown and North Battleford, Saskatchewan. Preliminary characterization of the isolates indicates that the collection consists of 16 actinomycetes, 4 yeasts and over 580 bacteria. Eighty percent of the isolates produced siderophores and the ability to inhibit the growth of Rhizoctonia and Pythium was observed in 11.6% and 7.5% of the isolates, respectively. Additional characterization of the isolates to be studied will be plant growth promotion, root colonization, growth at low temperature and identification

Biocontrol of damping-off and root-rot causing pathogens by novel Rhizobacteria isolated in Saskatchewan

Non-Peer ReviewedIn Saskatchewan, land area used to grow pulse crops is increasing, and maintenance of plant health is imperative to produce an economically viable resource. The objective of this study is to characterize novel rhizobacteria for plant growth promoting properties: enhancing the root and shoot growth of pea and lentil, and suppressing the growth and disease severity caused by fungal pathogens. From in vitro assays, isolates 5-6, 4-31, and 2-9 suppressed the growth of fungal pathogens. Mechanisms which suppress the growth of fungal pathogens may include the production of enzymes which degrade the cell wall of the fungi, and antifungal metabolites. In studies where rhizobacteria were inoculated in combination with commercial Rhizobium inoculants onto pea and lentil seeds, isolate 2-9 significantly increased the root dry weight of pea, and isolate 4-31 and 5-6 increased the ability of Rhizobium to fix nitrogen in pea and lentil, respectively. Fungicide compatibility studies using two commonly-used products (Apron®-FL, Crown®) showed that isolate 5-6 was compatible with both fungicides, whereas isolates 4-31 and 2-9 were compatible only with Apron®-FL. The three bacterial isolates (5-6, 4-31, and 2-9) chosen for possible development of a commercial inoculant show promise to be effective biological control agents against fungal pathogens

Enhancement of pulse crops: influence of novel rhizobacteria on the interaction of pea, lentil, and pathogenic fungi

Non-Peer ReviewedIn Saskatchewan, land area used to grow pulse crops (pea, lentil, bean, and chickpea) is increasing every year; between 2000 and 2001, an increase of 20% was recorded. Maintenance of plant health is imperative to produce an economically viable resource. The objective of this study is to characterize novel rhizobacteria for plant growth promoting properties: enhancing the development of pea and lentil plants, and suppressing the growth and disease severity caused by phytopathogenic fungi. Rhizobacterial isolates were selected from a preliminary group of 580 based on the ability to suppress Pythium, Rhizoctonia, and Fusarium spp. In in vitro assays, no one isolate, except for isolate 5-6, had shown the ability to strongly suppress all three pathogenic fungi. Additionally, the presence of pea or lentil seeds affected the ability of the strains to suppress the fungi. Bacterial cellfree filtrate suppressed the growth of Pythium and Rhizoctonia spp., thus fungal suppression is mediated by antifungal metabolites. Furthermore, suppression of Rhizoctonia sp. is correlated to the production of proteolytic enzymes by the rhizobacteria. Plant growth promoting rhizobacteria (PGPR) are important in food production by increasing crop productivity, and reducing crop losses caused by soil-borne phytopathogens

Influence of Alternaria spp. on susceptibility of canola and mustard to Pythium spp., Fusarium spp., and Rhizoctonia solani

Non-Peer ReviewedSeed exudates have been shown to inhibit the growth of some fungi responsible for seed rot and seedling blight in canola and mustard. Alternaria brassicae, A. alternata and A. raphani can all be found on seed of canola and mustard. Previous work indicates deep infections of Alternaria brassicae and A. raphani significantly reduce seed germination while A. alternata had no direct effect on germination. The objective of this study is to determine the effect of seed exudates on seed rot and seedling blight caused by Rhizoctonia solani, Fusarium spp. and Pythium spp. and determine if seed borne Alternaria is synergistic to these pathogens by breaking down defensive compounds in the seed exudates. Seed will be inoculated with Alternaria alternata. to create superficial surface infection. Susceptibility to Pythium, Fusarium and Rhizoctonia of artificially infected seed lots and naturally infected seed lots will be tested on water agar, blotter test and pot test. Seed exudates will also be obtained from seed lots after surface sterilization and bioassays of the ability of these exudates to support growth of pathogenic fungi and beneficial bacteria will be assessed

Crystallization of a classical two-dimensional electron system: Positional and orientational orders

Crystallization of a classical two-dimensional one-component plasma (electrons interacting with the Coulomb repulsion in a uniform neutralizing positive background) is investigated with a molecular dynamics simulation. The positional and the orientational correlation functions are calculated for the first time. We have found an indication that the solid phase has a quasi-long-range (power-law) positional order along with a long-range orientational order. This indicates that, although the long-range Coulomb interaction is outside the scope of Mermin's theorem, the absence of ordinary crystalline order at finite temperatures applies to the electron system as well. The `hexatic' phase, which is predicted between the liquid and the solid phases by the Kosterlitz-Thouless-Halperin-Nelson-Young theory, is also discussed.Comment: 3 pages, 4 figures; Corrected typos; Double columne

Ordered phase and scaling in ZnZ_n models and the three-state antiferromagnetic Potts model in three dimensions

Based on a Renormalization-Group picture of $Z_n$ symmetric models in three dimensions, we derive a scaling law for the $Z_n$ order parameter in the ordered phase. An existing Monte Carlo calculation on the three-state antiferromagnetic Potts model, which has the effective $Z_6$ symmetry, is shown to be consistent with the proposed scaling law. It strongly supports the Renormalization-Group picture that there is a single massive ordered phase, although an apparently rotationally symmetric region in the intermediate temperature was observed numerically.Comment: 5 pages in REVTEX, 2 PostScript figure

Impact of protists on a hydrocarbon-degrading bacterial community from deep-sea Gulf of Mexico sediments: A microcosm study

In spite of significant advancements towards understanding the dynamics of petroleum hydrocarbon degrading microbial consortia, the impacts (direct or indirect via grazing activities) of bacterivorous protists remain largely unknown. Microcosm experiments were used to examine whether protistan grazing affects the petroleum hydrocarbon degradation capacity of a deep-sea sediment microbial community from an active Gulf of Mexico cold seep. Differences in n-alkane content between native sediment microcosms and those treated with inhibitors of eukaryotes were assessed by comprehensive two-dimensional gas chromatography following 30-90 day incubations and analysis of shifts in microbial community composition using small subunit ribosomal RNA gene clone libraries. More biodegradation was observed in microcosms supplemented with eukaryotic inhibitors. SSU rRNA gene clone libraries from oil-amended treatments revealed an increase in the number of proteobacterial clones (particularly γ-proteobacteria) after spiking sediments with diesel oil. Bacterial community composition shifted, and degradation rates increased, in treatments where protists were inhibited, suggesting protists affect the hydrocarbon degrading capacity of microbial communities in sediments collected at this Gulf of Mexico site

The effect of urine concentration and pH on the growth of Escherichia coli in canine urine in vitro

Background: Lower urinary tract infections are common in dogs, and Escherichia coli is the most common bacterial pathogen isolated. The literature has conflicting evidence regarding the inhibitory effects of urine concentration and pH on E. coli growth. Hypothesis/Objectives: To determine the effect of different pH and urine concentrations on E. coli growth in vitro. Animals: Voided urine samples from 10 apparently healthy spayed female dogs were used. Methods: A matrix of 9 urine specific gravity (USG; 1.010, 1.020, and 1.030) and pH (5.5, 7.0, and 8.5) combinations was prepared by diluting and titrating filtered voided urine samples. Three E. coli isolates were obtained from urine of female dogs with signs of lower urinary tract infection and cultured at different urine pH and USG combinations in wells of a microtiter plate. The number of E. coli colony‐forming units (CFU) per mL of urine was calculated after aerobic incubation of the urine at 37°C for 18 hours, and statistically compared. Results: Significant differences were identified in the mean log CFU/mL among different combinations of pH and USG. The lowest log CFU/mL were observed in alkaline concentrated urine (pH 8.5 and USG 1.030). Conclusions and Clinical Importance: Escherichia coli in vitro growth was higher in neutral to acidic and diluted urine compared to alkaline and concentrated urine. The impact of non‐alkalizing diluting diets on the incidence of E. coli lower urinary tract infections should be further explored

Melting as a String-Mediated Phase Transition

We present a theory of the melting of elemental solids as a dislocation-mediated phase transition. We model dislocations near melt as non-interacting closed strings on a lattice. In this framework we derive simple expressions for the melting temperature and latent heat of fusion that depend on the dislocation density at melt. We use experimental data for more than half the elements in the Periodic Table to determine the dislocation density from both relations. Melting temperatures yield a dislocation density of (0.61\pm 0.20) b^{-2}, in good agreement with the density obtained from latent heats, (0.66\pm 0.11) b^{-2}, where b is the length of the smallest perfect-dislocation Burgers vector. Melting corresponds to the situation where, on average, half of the atoms are within a dislocation core.Comment: 18 pages, LaTeX, 3 eps figures, to appear in Phys. Rev.