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With the projected increase in global population, unprecedented increases in crop production will be needed and legume crops are one of the primary means of achieving these increases. The legume-Rhizobium symbiosis is the single most important source of biologically fixed nitrogen in agricultural systems but, as a biological system it is complex, and very sensitive to environmental effects, such as available soil nitrogen, soil pH (both high and low), soil salinity and extremes of soil temperature. Each of these may affect the delicate signal exchange process that occurs during symbiosis establishment. To better understand the effect of environmental factors on signal exchange and nodulation, we conducted four experiments, under controlled-environment conditions, with pea (Pisum sativum) as the model legume. The first experiment studied the effects of available nitrogen, the second the effects of low soil pH, the third the effect of soil salinity and the fourth the effects of low soil temperature. In all experiments the plants were inoculated with Rhizobium leguminosarum bv. viceae cells previously treated with 10 x 10-3 M of hesperitin or naringenin, or not treated (control). In all experiments plants were destructively sampled at 10, 20, 30 and 40 days after inoculation (in two experiments samplings were also conducted at 15 DAI), and data on plant and nodule variables were collected. To allow for a better understanding of the effects of flavonoids on nodule development an image analysis technique was developed that permitted us to measure every individual nodule at each sampling. This provided a more precise picture of nodule development over time than would have been possible with previous methods. Our results indicated that addition of flavonoids had positive effects on nodulation, both in number and size of nodules produced, and that the positive effects were greatest at the most inhibitory levels of the environmental factors tested, and at earlier sampling

Sitona lineatus L. (Coleoptera: Curculionidae) is a pest of Pisum sativum L. (Fabales: Fabaceae) and managing it is a challenge because of its fecundity, migratory behavior and concealed larval habitat. Potential components of an integrated pest management program for S. lineatus were investigated near Lethbridge and Vauxhall, Alberta over three years. Cage studies indicated that larval feeding is more damaging than adult feeding but that larval populations are not dependent on adult weevil density. In open plot experiments, thiamethoxam-treated plants experienced significantly less foliar feeding damage than plants receiving no insecticide treatment but no consistent effects on yield were observed for any plot treatment over six site-years. Rhizobium inoculation had a synergistic interaction with thiamethoxam. Laboratory trials showed that Bembidion quadrimaculatum L. (Coleoptera: Carabidae) consumed S. lineatus eggs. Seed treatment with thiamethoxam and Rhizobium inoculant, and egg predation should be included in an integrated pest management program for S. lineatus. / Plant Science

Thesis--Leyden. / In Periodical Room.

Iron is essential to the majority of microorganisms; it is an important cofactor in many cellular processes and enzymes. However in an aerobic environment and at biological pH, iron is primarily found as insoluble oxyhydroxides and is unavailable to microorganisms. Many bacteria have the ability to produce siderophores, low molecular weight compounds that have a high affinity for Fe3+. Siderophores are part of a multi-component system that actively transports the iron-siderophore complex into the cytoplasm. Rhizobia are characterized by their ability to form symbiotic relationships with leguminous plants, where they can fix nitrogen for the host plant and the plant provides the bacteria with nutrients. Under iron-limiting conditions, Rhizobia are known to produce siderophores. Rhizobium leguminosarum IARI 917 produces one dihydroxamate-type siderophore. This siderophore has been purified and chemically characterized. Results indicate that this strain is producing schizokinen, which has not been described in a member of the Rhizobia family.

Título de: Químico Ambiental / Los rizobios, bacterias simbiontes de leguminosas que fijan nitrógeno y sintetizan fitohormonas, pueden ser utilizados como alternativa a los fertilizantes químicos que generan efectos adversos sobre el medio ambiente. El efecto biofertilizante de los rizobios podría permitir el crecimiento de cultivos en suelos contaminados y reducir los efectos tóxicos de metales pesados. En este trabajo se investigó el efecto de Rhizobium leguminosarum sv phaseoli sobre los parámetros de crecimiento y tolerancia al Cu2+ de Phaseolus vulgaris (poroto común) Además se investigó el efecto de co-inocular las plantas con una mezcla de R. leg. phaseoli y Rhizobium etli así como la capacidad de R. leg. phaseoli de biosintetizar fitohormonas diterpénicas (giberelinas, GAs). Alternativamente las plantas se cultivaron en presencia de NH4NO3 y se investigó el efecto del Cu2+. La actividad de oxidasas de GAs se ensayó en bacteroides de R. leg. phaseoli aislados de nódulos radiculares, agregando precursores marcados con 14C. Las plantas inoculadas con R. leg. phaseoli presentaron, en la etapa de floración (30 días post-inóculo, dpi), una masa aérea similar a la de las plantas crecidas con NH4NO3 0,6 mM y una altura significativamente mayor, lo que sugiere el aporte de GAs bacterianas. Los bacteroides de R. leg. phaseoli, mostraron actividad de tres oxidasas de GAs: ent-kaurenoico oxidasa, C7 deshidrogenasa y C20 oxidasa, las que generan el producto final GA9, precursor de las GAs bioactivas. Éste podría ser convertido por el tejido vegetal del nódulo a GAs activas como fitohormonas. El co-inóculo de P. vulgaris con R. leg. x phaseoli más R. etli aumentó la masa de nódulos aunque no afectó significativamente los otros parámetros de crecimiento. Con respecto al efecto de Cu2+ en la solución de riego, se encontró que tanto las plantas inoculadas con R. leg. phaseoli como las crecidas con NH4NO3 presentaron síntomas macroscópicos de toxicidad a los 30 dpi, como caída de hojas y/o clorosis, en tanto que las plantas co-inoculadas presentaron escasos o nulos síntomas. Las plantas inoculadas con R. leg. phaseoli en presencia de Cu2+ 100 μM presentaron una masa seca aérea un 50% menor que la de las plantas crecidas con NH4NO3 y Cu2+, mientras que las plantas co-inoculadas presentaron un 71% de la masa seca aérea de las plantas crecidas con NH4NO3 y Cu2+. Esto sugiere que el co-inóculo favorecería la tolerancia a Cu2+ de P. vulgaris (mayor masa seca del tejido aéreo y escasos o nulos síntomas de toxicidad). Comparando los parámetros de crecimiento en ausencia y presencia de Cu2+ se encontró que las plantas co-inoculadas presentan un 85% de la masa seca aérea y un 82% de la altura en presencia de Cu2+100 μM con escasos o nulos síntomas de toxicidad, a diferencia de las plantas inoculadas con R. leg. phaseoli (menor masa seca aérea y caída de hojas o clorosis) o las plantas crecidas con NH4NO3 (masa seca aérea similar y síntomas macroscópicos de toxicidad). En conjunto los resultados sugieren que la mezcla de rizobios podría evaluarse en el futuro como potencial biofertilizante de P. vulgaris en terrenos contaminados con cantidades moderadas de Cu2+. / Rhizobia, leguminous symbionts that carry out nitrogen fixation and phytohormone biosynthesis, may be utilized as an alternative to chemical fertilizers which generate harmful environmental effects. The bacterial biofertilizer effect may also be helpful in reducing toxic effects of heavy metals in contaminates soils. In this work, the effect of Rhizobium leguminosarum sv. phaseoli on growth and copper tolerance of Phaseolus vulgaris (common bean) was investigated. Also the effect of co-inoculation with R. leg phaseoli plus Rhizobium etli was studied as well as the ability of R. leg phaseoli to synthesize diterpene phytohormones (gibberellins, GAs). Alternatively, P. vulgaris was grown in the presence of NH4NO3 and the effect of Cu2+ was investigated under this condition. GA oxidase activities were assayed with R. leg phaseoli bacteroids isolated from root nodules, by adding exogenous 14C-labelled substrates. Plants inoculated with R. leg phaseoli showed, at flowering, an aereal dry weight similar to that of plants grown with NH4NO3 0,6 mM but were significantly taller suggesting bacterial GA biosynthesis. Isolated R. leg phaseoli bacteroids showed activity of three of the GA oxidases: ent-kaurenoic acid oxidase, C7 dehydrogenase and C20 oxidase, involved in GA9 biosynthesis. This product, inactive as phytohormone, could be converted by the nodule plant tissue into a bioactive product. Co-inoculation with R. leg phaseoli plus R. etli increased nodule weight but did not significantly affect other growth parameters. xii In reference to the effect of Cu2+, P. vulgaris inoculated with R. leg phaseoli or grown with NH4NO3 showed macroscopic toxicity symptoms at flowering in the presence of this metal ion like leaf abscission or chlorosis, while co-inoculated plants showed almost no toxicity symptoms. The aereal dry weight of plants inoculated with R. leg phaseoli and grown with 100 μM Cu+2 was 50% less than that of plants grown with NH4NO3 and 100 μM Cu+2 in contrast to co-inoculated plants that kept 71% of the aereal dry weight. These results suggest that co-inoculation would favor Cu2+ tolerance in P. vulgaris (higher aereal dry weight and almost no macroscopic toxicity symptoms). Comparison of growth parameters in the presence and absence of Cu2+ indicated that co-inoculated plants present an 85% of the aereal dry weight of plants grown without Cu2+ and 82% of their height with no toxicity symptoms, in contrast to plants inoculated with R. leg phaseoli or grown with NH4NO3 that showed macroscopic toxicity symptoms and less dry weight of aereal tissue. Co-inoculation with R. leg phaseoli plus R. etli could be further evaluated as a potential biofertilizer for P. vulgaris in soils discretely contaminated with Cu2+.