This study was undertaken to characterize the nod and sdh operons of Bradyrhizobium japonicum and Sinorhizobium meliloti. Ten putative B. japonicum mutants with altered nod gene induction characteristics were isolated by screening mutants for genistein-independent nod gene expression. The mutants were found to have higher nodY expression than the wild-type in the presence of genistein. The increased sensitivity of all mutants to genistein was more apparent under suboptimal inducer concentration (0.1muM) and/or temperature (15°C). The expression of nodY gene induction was determined for five strains (Bj30050, 53, 56, 57, 58) under different temperature and inducer conditions. These five strains were also found to produce more lipochitooligosaccharide than the wild-type, at both 25°C and 15°C. Three of the ten mutant strains (including Bj30056 and 57) were unable to fix nitrogen with soybeans grown at optimal temperatures. Based on nodY gene expression and symbiotic phenotype the B. japonicum mutants were classified into three groups. / A molecular genetic approach was taken to investigate the regulation of expression of succinate dehydrogenase (SDH) in S. meliloti. The sdhCDAB genes encoding SDH were shown by RT-PCR to be co-transcribed and thus constitute an operon. The transcriptional start site and putative promoter region of the first gene in the operon, sdhC , were identified by 5'-RACE and DNA sequence analysis. Transcriptional lacZ fusions to sdhC indicated that expression of the operon is regulated by carbon source in the growth medium but not by growth phase. The highest expression of the sdh operon was observed in cells grown with acetate, arabinose and glutamate, as sole carbon sources, and the lowest expression was observed in cells grown with glucose and pyruvate as sole carbon sources. / Also presented is the isolation and characterization of the first defined sdh mutant in a rhizobial species. The mutants helped demonstrate that the total lack of SDH activity would be lethal to S. meliloti cells. Symbiotic phenotype of the mutants indicated that SDH is required for N2-fixation.

In the N2 fixing legume symbiosis, mineral nitrogen (N) not only decreases N2 fixation, but also delays and inhibits the formation and development of nodules. The purposes of this thesis were to elucidate the role of signaling in the mineral N effects on nodulation and nitrogen fixation in soybean [Glycine max (L.) Merr.] and to attempt to find ways to overcome this inhibition. The responses of soybean plants, in terms of daidzein and genistein synthesis and exudation, to different mineral N levels were studied. Daidzein and genistein distribution patterns varied with plant organs, mineral N levels, and plant development stages. Mineral N inhibited daidzein and genistein contents and concentrations in soybean root and shoot extracts, but did not affect root daidzein and genistein excretion in the same way. In both synthesis and excretion, daidzein and genistein were not affected equally by mineral N treatments. Variability existed among soybean cultivars in the responses of root daidzein and genistein contents and concentrations to mineral N levels. The amount of daidzein and genistein excreted by soybean roots did not always correspond to the daidzein and genistein contents and concentrations inside the roots. On the Bradyrhizobium japonicum side, nod gene expression was inhibited by mineral nitrogen. Genistein was used to pre-incubate B. japonicum cells or was applied directly into the plant growing medium. The results showed that genistein manipulation increased nodule weight and nodule nitrogen fixation under greenhouse conditions, but interactions existed among soybean cultivars, genistein concentrations and nitrate levels. Similar results were found under field conditions. Soybean yield was increased on sandy-loam soil by preincubation of B. japonicum cells with genistein. Addition of genistein beginning at the onset of nitrogen fixation also improved soybean nodulation and nitrogen fixation. Soybean cultivars had different sensitivities to genistein additi / Other studies also show that temperature affected genistein and daidzein content and concentration in soybean roots. The effect of temperature varied among soybean cultivars. Some PGPR strains can mitigate the negative effects of nitrate on soybean nodulation and nitrogen fixation, however, this is influenced by soybean genotype. Applying PGPR together with genistein preincubation of B. japonicum cells improved soybean nodulation and increased yield. The level of improvement varied among soybean cultivars and PGPR strains. Preincubation of B. japonicum cells with genistein improved strain competitiveness under greenhouse, but not field conditions. / Overall, these findings suggested that both plant-to-Bradyrhizobium and Bradyrhizobium-to-plant signals play important roles in the effects of mineral N on nodulation and N fixation. Signal manipulation could partially overcome the inhibitory effects of mineral N on soybean- B. japonicum N fixation symbiosis.

One of the major limitations to obtain satisfactory soybean (Glycine max (L.) Merr.) yield in acid soils in many developing countries is the purchasability of liming materials. For many low income farmers, liming to the 'ideal' soil pH of 6.5 using conventional methods is usually too expensive. Pot and field studies were conducted to determine whether satisfactory soybean growth could be obtained by reducing the amount of lime applied and the volume of soil limed. The Quebec soils used in these studies were a Gray-brown Luvisol (pH 5.1) and a Humic Gleysol (pH 5.3) in the pot study and a Gray-brown Luvisol (pH 5.1) and a Dark-gray Gleysol (pH 6.1) in the field study. / Results suggest that localizing the lime in acid Quebec soils would be a more efficient use of the liming material. Further studies in tropical acid soils are required to determine if the localized placement of lime is a viable practice for third-world, low income farmers. (Abstract shortened by UMI.)

Since the early 1990s, the concept of substantial equivalence has been a guiding principle of the Canadian Food Inspection Agency and Health Canada's regulatory approach toward products of plant biotechnology destined for the food and livestock feed markets. To assess substantial equivalence in terms of chemical composition, genetically modified (GM) plants are compared to conventional counterparts at the level of macro- and micro-nutrients, allergens and toxicants. Such targeted comparative analyses are limited in their scope and their capacity to detect unintended changes in chemical composition. There is a need to develop more effective testing protocols to improve the substantial equivalence assessment of GM crops. The objective of this thesis was to explore high-density oligoarrays as tools to assess substantial equivalence of Roundup Ready(TM) soybean. Three conventional and two GM soybean varieties were selected according to the similarity of their performance in field trials. Total RNA was extracted from first trifoliate leaves harvested from soybean plants grown in a controlled environment until the V2 stage. To annotate the 37 776 soybean probesets present on the multi-organism Soybean Affymetrix GeneChip(TM), consensus sequences were aligned with TIGR Soybean Gene Index tentative consensus sequences using BLASTN. After redefining the chip description file to exclude non-soybean probesets, the effects of three different normalization methods (Robust Multichip Average (RMA), Microarray Analysis Suite (MAS 5.0) and Model-Based Expression Index) were compared and Significance Analysis of Microarrays (SAM for R-Bioconductor) was applied to detect differential gene expression between conventional and GM soybean varieties. Eleven candidate genes were selected for further studies.

No description available.

Soybean rust (SBR), caused by the fungus Phakopsora pachyrhizi Syd., is a real threat to soybean crops in South Africa. Its ability to spread rapidly and its potential to severely reduce yields have earned it the reputation as the most destructive foliar disease of soybeans. SBR has been reported in South Africa every year since its arrival in 2001. While extensive research had been done on the epidemiology and fungicide application requirements in South Africa, no work into the long term climatic vulnerability of soybean production areas to SBR had been done. This meant soybean producers do not know whether SBR is a threat in their areas. Through this research a SBR algorithm was developed using readily available climate data, viz. temperature and rainfall, to create a daily index specifying the climatic vulnerability of SBR infection. The algorithm was applied to a 50 year historical climate database, and a series of maps was created illustrating the long term vulnerability of different areas to SBR infection. These maps allow soybean producers to understand the climatic vulnerability of their area to SBR infection. Time series graphs were created for selected key soybean production areas to allow soybean producers to distinguish periods of high and low climatic risk during the season. This may help with decisions regarding the planting times, the maturation rate of different cultivars as well as the timing and application of fungicides. The framework for a near real time forecasting system was created outlining how the system could amalgamate recently recorded and forecasted weather data, run it through the SBR algorithm and provide a near real time, as well as forecasted vulnerability, based on the climatic conductivity for SBR infection. Anticipated limitations and difficulties on developing the forecasting system are also outlined. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

In this study, lipo-chitooligosaccharide (NodBj-V (C 18:1, MeFuc); LCO) 10-7M, extracted from Bradyrhizobium japonicum, was sprayed on the leaves of soybean cv. OAC Bayfield soybean and Evans x L66-2470 (carrying the rj1 mutation, and unable to nodulate). Leaf SA level and activities of the PR proteins chitinase, beta-1,3-glucanase and guaiacol peroxidase (GPOX) were quantified. Phenylalanine ammonia-lyase 1 (PAL1) and isoflavone synthase 2 (IFS2) relative gene expression levels in the sprayed leaves were quantified using quantitative real-time PCR. Messenger RNA abundance was quantified using microarrays. The treatment caused a transient increase in local salicylate levels 24 h after exposure, and a systemic increase in GPOX activity 48 h after exposure, in both soybean types. Of the selected 38 genes affected by the LCO treatment, 25 were stress-related. There were no significant differences in (A) chitinase and beta-1,3-glucanase activity, or (B) in PAL1 and IFS2 gene expression.

The major downfalls of vegetable oils, namely soybean oil in this research, are very detrimental to engine lubricant performance. A unique - out of the box- additive package is needed to compensate for the lubricant deficiencies. This research searched for unique additive solutions to the problems of oxidation and heat stability, low temperature pumpability, and fluid corrosiveness. The additive solutions were then tested in preliminary engine tests. In this research, several formulations were developed that passed the main engine oil low temperature test, the mini rotary viscometer. The lubricants met the passing viscosity requirements of 60,000 centipoise and exhibited no yield stress. The formulation was tested using ASTM D 6594[1], hot tube corrosion bench test, and Sequence VIII corrosion engine test. Acceptable results were seen in both tests. Oxidation bench tests were used to examine soybean engine oil stability. Several antioxidants showed improved performance in the TFOUT oxidation induction time bench test. A mixture of those antioxidants was tested in the Sequence IIIG engine test. All of the formulas failed the Sequence IIIG tests. However, improved test results were seen when the soybean oil was decreased from 15 wt % to 5 wt % in the formulations.

The normalized difference vegetative index (NDVI) has been correlated with physiological plant parameters and used to evaluate plant growth. There is little information about the use of this technique to detect soybean nutrient deficiencies. The objective of this work was to determine the ability of the NDVI sensor to detect P and K deficiencies, and grain yield reduction, in soybean. During 2010 and 2011, NDVI measurements were made on a soybean field trial site known to exhibit yield responses to both P and K nutrition. Four replicates of 8 levels each of P and K nutrition were evaluated. The NDVI measurements were made with an active proximal sensor held parallel to the soil surface every seven days after V2, and until R2. At each measurement a mean NDVI value was found for each plot. Phosphorus deficiency was detected with the first NDVI measurement. Potassium deficiency was first detected just after V4. Differences in NDVI values due to P or K nutrition increased with continued crop development. There were significant R1 leaf composition and grain yield responses to improved P or K nutrition. The active proximal sensor was able to detect soybean growth differences due to P or K deficiencies in soybean.

Agricultural intensification to increase food, feed, and fibre production has also resulted in environmental degradation, including poorer soil quality and high emissions of greenhouse gases (GHGs) like nitrous oxide (N2O). Intercropping, an agroecosystem management practice where more than one crop is planted on the same plot of land at the same time, promotes the complementary use of soil nutrients, and may improve soil quality and increase the retention of inorganic nitrogen (N) in the soil, thereby reducing N2O emissions. An experiment was conducted in Balcarce, Argentina to determine the impact of intercropping maize (Zea mays L.) and soybean (Glycine max (L.) Merr.), (either 1:2 or 2:3 rows of maize to soybean) on soil quality and soil N transformations after six cropping seasons. It was found that intercropping significantly improved soil quality over a six year period, as indicated by the soil organic carbon (SOC), soil total nitrogen (TN), soil light fraction organic matter (LF), and soil microbial biomass carbon (SMB-C). However, the soil quality also significantly improved in the sole crops over this time, and in 2012, only SMB-C was significantly (p<0.05) greater in the 2:3 intercrop than in the sole crops. Intercropping resulted in higher rates of gross nitrogen (N) mineralization than the sole crops, and the 2:3 intercrop resulted in higher rates of gross N immobilization than in the other treatments. However, the high rate of gross N mineralization resulted in a low relative NH4+ immobilization in both intercrops, signifying a lower potential for reducing soil NH4+ concentrations than in the sole crop treatments. Net N immobilization occurred in all treatment plots, which was desired at the end of the fallow period to reduce N losses from the soil. The 2:3 intercrop appeared to perform better than the 1:2 intercrop. However, further research needs to be conducted to determine the seasonal variations in N mineralization and immobilization, and to further examine the intercrop spatial arrangements to increase crop residue yield.