Thesis (doctoral)--Swedish University of Agricultural Sciences, 2000. / Includes bibliographical references.

Sclerotinia stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary is an economically important pathogen on canola (Brassica nanups L.). Due to the increasing public concerns of fungicide usage and the limitations of cultural methods, biological control is emerging as a promising alternative to control S. sclerotiorum in an environmentally-friendly way. Several bacterial strains, mainly Bacillus spp., were isolated from canola and wheat plants. Eight Gram-positive bacterial strains were inhibitory against mycelial growth of S. sclerotiorum in intro. Three Bacillus spp., one Staphylococcus spp. and one Pseudomonas spp. (control) were tested in whole plant assays, and all of them achieved significant (P<0.05) disease suppression. An experiment in the greenhouse to investigate the optimal time of application showed that the highest disease suppression was achieved when B. amyloliquefaciens BS6 was inoculated at the same time as the pathogen. The field experiment (Trial two) in 2003 showed a significant (P<0.05) reduction of disease incidence and severity in bacteria-pre-treated plots, compared to control plots, even though the survival of bacterial populations of Pseudomonas chlororaphis PA-23 and B. amyloliquefaciens BS6 were low on the petals’ surface. The bacterial strains were effective against S. sclerotiorum under laboratory, greenhouse, and field conditions, and these results also suggest that antibiosis and plant induced resistance might be involved in the disease suppression. To identify antibiotic-related genes in these potential biocontrol bacterial agents, polymerase chain reaction (PCR) with specific primers was used. The sequencing of PCR products and BLAST search in the gene bank showed that P. chlororaphis PA-23 contains biosynthetic genes for phenazine-1-carboxylic acid, pyrrolnitrin and probably 2,4-diacetylphloroglucinol, and that B. thuringiensis/cereus BS8, B. cereus L and B. mycoides S contain zwittermicin A self-resistant gene. The significance of the presence of these genes is discussed. Induced resistance mediated by S. sclerotiorum and B. amyloliquefaciens BS6 was evaluated in a greenhouse study followed by analysis of the phenolic compounds from canola leaf extracts by high performance liquid chromatography (HPLC). Pre-treatment with bacteria significantly (P<0.05) reduced the disease symptoms on canola plants. The HPLC results indicated that the disease suppression from the bacterial pre-treatment was related to the induction of secondary metabolites in canola leaves. The HPLC results also showed that the inoculum of S. sclerotiorum was also associated with the induction of these compounds in canola leaves. The knowledge accumulated during this study has shown that the bacterial biocontrol agents tested have a great potential in controlling sclerotinia stem rot of canola. The understanding of the biocontrol mechanisms involved in the disease suppression would help optimize their biocontrol efficiency. Therefore, further studies on the role of bacterial antibiotics in disease suppression, and better understanding of plant induced resistance mediated by pathogen and bacterial agents are needed. / October 2004

Sclerotinia stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary is an economically important pathogen on canola (Brassica nanups L.). Due to the increasing public concerns of fungicide usage and the limitations of cultural methods, biological control is emerging as a promising alternative to control S. sclerotiorum in an environmentally-friendly way. Several bacterial strains, mainly Bacillus spp., were isolated from canola and wheat plants. Eight Gram-positive bacterial strains were inhibitory against mycelial growth of S. sclerotiorum in intro. Three Bacillus spp., one Staphylococcus spp. and one Pseudomonas spp. (control) were tested in whole plant assays, and all of them achieved significant (P<0.05) disease suppression. An experiment in the greenhouse to investigate the optimal time of application showed that the highest disease suppression was achieved when B. amyloliquefaciens BS6 was inoculated at the same time as the pathogen. The field experiment (Trial two) in 2003 showed a significant (P<0.05) reduction of disease incidence and severity in bacteria-pre-treated plots, compared to control plots, even though the survival of bacterial populations of Pseudomonas chlororaphis PA-23 and B. amyloliquefaciens BS6 were low on the petals’ surface. The bacterial strains were effective against S. sclerotiorum under laboratory, greenhouse, and field conditions, and these results also suggest that antibiosis and plant induced resistance might be involved in the disease suppression. To identify antibiotic-related genes in these potential biocontrol bacterial agents, polymerase chain reaction (PCR) with specific primers was used. The sequencing of PCR products and BLAST search in the gene bank showed that P. chlororaphis PA-23 contains biosynthetic genes for phenazine-1-carboxylic acid, pyrrolnitrin and probably 2,4-diacetylphloroglucinol, and that B. thuringiensis/cereus BS8, B. cereus L and B. mycoides S contain zwittermicin A self-resistant gene. The significance of the presence of these genes is discussed. Induced resistance mediated by S. sclerotiorum and B. amyloliquefaciens BS6 was evaluated in a greenhouse study followed by analysis of the phenolic compounds from canola leaf extracts by high performance liquid chromatography (HPLC). Pre-treatment with bacteria significantly (P<0.05) reduced the disease symptoms on canola plants. The HPLC results indicated that the disease suppression from the bacterial pre-treatment was related to the induction of secondary metabolites in canola leaves. The HPLC results also showed that the inoculum of S. sclerotiorum was also associated with the induction of these compounds in canola leaves. The knowledge accumulated during this study has shown that the bacterial biocontrol agents tested have a great potential in controlling sclerotinia stem rot of canola. The understanding of the biocontrol mechanisms involved in the disease suppression would help optimize their biocontrol efficiency. Therefore, further studies on the role of bacterial antibiotics in disease suppression, and better understanding of plant induced resistance mediated by pathogen and bacterial agents are needed.

The fungal plant pathogen <I>Sclerotinia sclerotiorum</I> (Lib.) de Bary is responsible for disease in a wide range of crops throughout the world. Sclerotinia disease, or cottony soft rot, in carrot (<I>Daucus carota</I> L.) crops is generally a post-harvest problem during storage. Research has, therefore, focused in this area. However, little attention has been paid to foliar and root crown damage caused by <I>S. sclerotiorum</I> during crop development, a problem prevalent in crops in the North East of Scotland. The conventional method for controlling <I>S. sclerotiorum</I> in the developing crop is fungicide application, which often gives only partial control. There is no recognised effective control method in organic systems. This study investigated a diverse array of potential control methods, involving combinations of cultural, biological, environmental and forecasting methods, all lying within the confines of organic regulations. A number of germination characteristics of the <I>S. sclerotiorum</I> sub-population in question were studied. Steam sterilisation of soil was then investigated as a possible replacement for methyl bromide fumigation. Steam was shown to have potential control properties regarding sclerotia of <I>S. sclerotiorum</I>, if combined with manipulation of soil matric potential. Commercially available biological control agents, soil amendments and conventional fungicides were compared in the search for the most effective control for Sclerotinia. The product found to be most effective in this group, and acceptable for use in organic systems, <I>Coniothyrium minitans,</I> was further investigated in combination with organically produced compost and readily soluble nitrogen fertiliser. <I>C. minitans</I> provided a level of control in both instances. The application of high levels of nitrogen fertiliser encouraged severe infections, as did excessive irrigation of crops. A number of methods and practices were unsuccessfully applied, or suggested by the studies, that can reduce the incidence of disease caused by <I>S. sclerotiorum</I> in carrot crops in North East Scotland, and are acceptable to both conventional and organic systems.

Sclerotinia stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary is an economically important pathogen on canola (Brassica nanups L.). Due to the increasing public concerns of fungicide usage and the limitations of cultural methods, biological control is emerging as a promising alternative to control S. sclerotiorum in an environmentally-friendly way. Several bacterial strains, mainly Bacillus spp., were isolated from canola and wheat plants. Eight Gram-positive bacterial strains were inhibitory against mycelial growth of S. sclerotiorum in intro. Three Bacillus spp., one Staphylococcus spp. and one Pseudomonas spp. (control) were tested in whole plant assays, and all of them achieved significant (P<0.05) disease suppression. An experiment in the greenhouse to investigate the optimal time of application showed that the highest disease suppression was achieved when B. amyloliquefaciens BS6 was inoculated at the same time as the pathogen. The field experiment (Trial two) in 2003 showed a significant (P<0.05) reduction of disease incidence and severity in bacteria-pre-treated plots, compared to control plots, even though the survival of bacterial populations of Pseudomonas chlororaphis PA-23 and B. amyloliquefaciens BS6 were low on the petals’ surface. The bacterial strains were effective against S. sclerotiorum under laboratory, greenhouse, and field conditions, and these results also suggest that antibiosis and plant induced resistance might be involved in the disease suppression. To identify antibiotic-related genes in these potential biocontrol bacterial agents, polymerase chain reaction (PCR) with specific primers was used. The sequencing of PCR products and BLAST search in the gene bank showed that P. chlororaphis PA-23 contains biosynthetic genes for phenazine-1-carboxylic acid, pyrrolnitrin and probably 2,4-diacetylphloroglucinol, and that B. thuringiensis/cereus BS8, B. cereus L and B. mycoides S contain zwittermicin A self-resistant gene. The significance of the presence of these genes is discussed. Induced resistance mediated by S. sclerotiorum and B. amyloliquefaciens BS6 was evaluated in a greenhouse study followed by analysis of the phenolic compounds from canola leaf extracts by high performance liquid chromatography (HPLC). Pre-treatment with bacteria significantly (P<0.05) reduced the disease symptoms on canola plants. The HPLC results indicated that the disease suppression from the bacterial pre-treatment was related to the induction of secondary metabolites in canola leaves. The HPLC results also showed that the inoculum of S. sclerotiorum was also associated with the induction of these compounds in canola leaves. The knowledge accumulated during this study has shown that the bacterial biocontrol agents tested have a great potential in controlling sclerotinia stem rot of canola. The understanding of the biocontrol mechanisms involved in the disease suppression would help optimize their biocontrol efficiency. Therefore, further studies on the role of bacterial antibiotics in disease suppression, and better understanding of plant induced resistance mediated by pathogen and bacterial agents are needed.

Thesis (Ph. D., Plant Science)--University of Idaho, December 2008. / Major professor: Shree P. Singh. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 93-97). Also available on the World Wide Web.

Thesis (Ph. D., Soil and Land Resources)--University of Idaho, May 2007. / Major professor: Guy R. Knudsen. Includes bibliographical references. Also available online (PDF file) by subscription or by purchasing the individual file.

Thèse (M.Sc.)--Université Laval, 2003. / Titre de l'écran-titre (visionné le 29 mars 2004). Bibliogr.

Sclerotinia stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary is an economic disease affecting canola (Brassica napus L). Since expression of sclerotinia stem rot symptoms shows much variability and the trait is quantitative in nature, reliable phenotypic evaluation methods for characterization are needed. The three major objectives of this dissertation were to: i) evaluate eight different inoculation methods to discriminate between S. sclerotiorum-resistant and susceptible B. napus germplasm; ii) develop breeding lines with resistance to multiple diseases, and; iii) to identify QTL associated with resistance to sclerotinia stem rot using association mapping (AM). The eight methods evaluated were the detached leaves, detached stems, petiole inoculation (PIT), straw-inoculation, stem-piercing with toothpick, mycelial spray (MSI), petal inoculation and oxalic acid assay. MSI and PIT can better discriminate between the isolates and germplasm. Breeding lines resistance to S. sclerotiorum, Leptosphaeria maculans, and Rhizoctonia solani were developed from a cross between two moderately sclerotinia stem rot resistant plant introductions (PI). F2 seedlings were screened for sclerotinia stem rot using PIT. Surviving plants were self pollinated and their progeny screened again. This process was repeated until the F6 generation. In addition, F5 seedlings were evaluated for their reaction to R. solani and F5 and F6 seedlings for their reaction to L. maculans. Eight lines were identified as moderately resistance to these three pathogens. The genomes of a group of 278 B. napus plant introductions were screened using Diversity Array Technology to detect QTL associated with resistance to sclerotinia stem rot. The population was classified into nine sub-populations and 32 significant markers each explaining between 1.5 and 4.6% of the variation were identified. Blastn search indicates that similar nucleotide sequences are distributed throughout the genomes of B. oleracea, B. rapa, and A. thaliana. Results of these studies suggest the PIT and MSI are reliable screening tools to evaluate materials for resistance to sclerotinia stem rot; materials identified as resistant to S. sclerotiorum were also moderately resistant against R. solani and L. maculans and could be valuable sources for canola improvement programs; and AM allowed us to identify QTL associated with resistance to sclerotinia stem rot.