Soybean (Glycine max (L.) Merr.) is one the major crops produced worldwide. However, soybean is susceptible to many diseases. Sclerotinia stem rot (SSR) disease caused by Sclerotinia sclerotiorum (Lib.) de Bary is considered one of the most important fungal diseases of soybean. It can be controlled by chemicals (e.g. fungicides), by breeding cultivars with disease resistance and by cultural control (e.g. increasing the width between rows, reducing plant populations). A promising and complementary method of controlling SSR disease in the field is the application of biological control agents. Biological control agents introduced in a soil environment will interact with other soil food web organisms, as do the pathogenic organism and infected plants, which may change the genetic and functional diversity in soil microbial communities. Profiling these changes may lead to an improved understanding of the interactions between these players (biological control agents, pathogens, soil biota and plants) in the biological control phenomenom, permiting us to exploit naturally-occurring ecological relationships and develop more sustainable approaches to control soybean diseases. Fatty acid biomarkers analysis was used to profile microbial communities in soils. Two laboratory studies were conducted to evaluate the methods used for extraction and profiling the fatty acid biomarkers from soil samples with a range of soil properties (clay content, organic matter content), The first study investigated the best solvent mixture for recovering fatty acid biomarkers from soil using an automated pressurized solvent extraction (PSE) system. Solvent mixtures containing chloroform and methanol were more efficient at extracting fatty acids from agricultural soils than hexane:2-propanol and acetone. The second study presented an exploratory pyrolysis-mass spectrometry technique to rapidly fingerprint soil lipids extracted from different agroecosystems. Pyrolysis-mass spectrometry discriminated among soils and crop production systems in the same way as the fatty acid profiling. I also report on the efficicacy of biological control agents to control Sclerotinia stem rot disease in soybean. A two-year study was conducted in soybean fields under conventional or no tillage to determine whether Trichoderma virens (SoilGard(TM)) and arbuscular mycorrhizal fungi (a mixture of Glomus intraradices and G. mosseae ), used alone or in combination, could reduce sclerotinia stem rot (SSR) disease incidence. Generally, SSR disease indicators, as well as the soybean yield, were not affected significantly by the biological control treatments. I then studied whether changes in microbial community composition were related to the inoculation of the biological control agents and the disease incidence in soybean fields. Inoculation of biological control agents changes the expression of many soil fatty acids during both years of the trial. Also, in the plots with severely diseased plants, fatty acids biomarkers of gram positive and actinomycetes bacteria were significantly greater than in plots with healthy plants. I conclude that further improvement in laboratory techniques and procedures will permit researchers to efficiently extract and characterize soil lipids, providing new insight into soil organic matter dynamics and soil microbial ecology. Further study will be needed to verify the efficacy and optimize the application method, dose and timing of biocontrol agents to provide protection against SSR disease in soybean fields.

Allium white rot (AWR) is a soilborne disease that seriously damages commercial cultivation of onion (Allium cepa) and garlic (Allium sativum) crops. The disease has been found everywhere onions are cultivated and at present no system of control has been found that fully prevents the occurrence of the disease. The fungus responsible for the disease, Sclerotium cepivorum, uses oxalic acid to kill Allium bulb and root tissue in growing onion and garlic plants. Research suggests recombinant oxalate oxidase and oxalate decarboxylase enzymes may be able to degrade this acid and confer resistance against pathogens that rely on it, such as Sm. cepivorum or Sclerotinia sclerotiorum. To test the efficacy of these enzymes against white rot pathogens, three transgenes for wheat oxalate oxidase, barley oxalate oxidase and Flammulina oxalate decarboxylase were transformed into onions and garlic by Agrobacterium-mediated transformation. Allium species are highly recalcitrant to transformation, so these three transgenes were also transformed into tobacco to provide fast-recovering, easy to test transformants to assess the efficacy of the transgenes. Transformed garlic and tobacco lines were analysed to assess the integration and expression of the transgenes, then challenged with Sm. cepivorum or Sa. sclerotiorum, respectively, to assess the bioactivity of recombinant wheat oxalate oxidase, barley oxalate oxidase, and Flammulina oxalate decarboxylase against oxalic acid-dependent pathogens. Results show that one line of tobacco expressing the Flammulina oxalate decarboxylase enzyme was found to be consistently resistant to Sclerotinia sclerotiorum. Garlic lines transformed with this transgene failed to display stable transgene expression or disease resistance, possibly due to silencing of the transgene in recovered transformant tissue.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Thèse (Ph. D.)--Université Laval, 2005. / Titre de l'écran-titre (visionné le 13 févr. 2008). Bibliogr.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2008. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on June 29, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy Plant Science, Department of Agricultural, Food and Nutritional Science, University of Alberta." Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaves 116-136). Also available on the World Wide Web.

Thesis (M.Sc.) - University of KwaZulu-Natal, Pietermaritzburg, 2007. / Full text also available online. Scroll down for electronic link.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 47-54). Also available on the World Wide Web.