Reports concerning the life history of Plasmodiophora brassicae Wor. are highly conflicting. The contradictions in the literature on the subject and the difficulties encountered in the initial phase of the present investigation brought about an inquiry into the techniques employed by previous workers. Repetition of these techniques indicated that many previous experiments had not taken into consideration the problems inherent in an in vitro study of Plasmodiophora brassicae. Conclusions drawn from such experiments are thus of doubtful value. Methods described as successful by earlier investigators were employed in an attempt to stimulate germination. The germination process was not observed, and contaminants introduced with the resting spore material made it impossible to designate any one motile organism as P. brassicae. Attempts were made to obtain root hair infection. Pour methods described by previous investigators proved unsuccessful. A limited degree of infection was obtained by placing young cabbage and cauliflower seedlings in a buffered nutrient solution containing washed P. brassicae resting spores. In spite of the fact that artifacts were readily produced, early infection stages were observed and photographed and the existence of a zoosporangial stage in the root hair was confirmed. The infection rate was too low to permit intensive observations of the development of the parasite within the root hair. A proteolytic enzyme preparation was somewhat successful in increasing the infection rate. This was taken as an indication that a combination of enzymes could provide the necessary germination stimulus. Decay of the host tissues is apparently necessary to the maturation of the resting spores. Present experiments indicated that it is not feasible to separate the contaminants from these spores. As it was not possible to draw conclusions from contaminated cultures, it is concluded that the only approach of value is to provide an artificial germination stimulus to spores from clean clubs, so that the development of the parasite may take place under sterile conditions. / Land and Food Systems, Faculty of / Graduate

No description available.

Clubroot disease, caused by Plasmodiophora brassicae, poses a threat to the Canadian canola industry, and breeding of resistant cultivars is urgent. The objective of this study was to identify Brassica germplasm possessing resistance to Canadian P. brassicae pathotypes based on greenhouse screening. Germplasm resistant to local pathotype(s) is the prime requirement for breeding clubroot resistant cultivars. Race-specific to broad-spectrum resistance was identified in the diploid species B. rapa (AA) and B. oleracea (CC), and in the amphidiploid B. napus (AACC). The diploid B. nigra (BB) also showed race-specific to broad-spectrum resistance; however, the two amphidiploids with B. nigra as one of the parental species viz., B. juncea (AABB) and B. carinata (BBCC) were completely susceptible. The occurrence of resistance in the diploid and amphidiploid Brassica species is discussed in the light of their evolution, and a differential set for identification of Canadian clubroot pathotypes is proposed. / Plant Science

vii, 137 leaves : photos, (Part col.), graphs, tables ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Entomology, 1979

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1942. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: leaves 47-49.

The aim of this project was to develop treatments that would be able to reduce the survival of clubroot spores in field soil and protect the roots of young transplants against infection. The project focused on using combinations of treatments which integrate novel and existing controls with emphasis placed on the sustainable use of waste materials, plant materials and bioactives. A wide range of treatments were screened individually and in combination under glasshouse and field conditions, e.g. fungicides, nutritional amendments, companion planting, plant saponins and biocontrol agents. Many of these treatments were able to reduce clubroot severity to varying degrees. Glasshouse treatments were more successful at controlling disease than those applied in the field. The most effective treatments - when applied correctly - contained calcium, e.g. lime as calcium oxide or LimeX (a by-product of the sugarbeet processing industry), and crushed scallop and whelk shells (a by-product of the fishing industry). Whilst the effects of calcium and pH on clubroot are not new, growers need to think more in terms of dose of calcium applied in the field rather than just pH, and also, the time of addition of lime to soil before planting needs serious consideration as it may be optimal to apply lime less than two weeks before transplanting. Experimental results have shown that soil microflora plays a major role in the development of clubroot disease and that the membrane potential of growing roots may be one of the most important factors in preventing P. brassicae from entering plant roots and causing disease due to the effect that calcium and pH have on clubroot control. The experiments have also shown that there are interactions between treatments such as fungicides, limes, soil nutritional level and soil microflora at controlling disease and some treatments may reduce the effectiveness of other treatments at controlling disease. Another factor that is known to affect the effectiveness of treatments at controlling clubroot is the initial spore load in the soil. Therefore, an additional aim of the project was to develop a rapid, quantitative PCR based diagnostic test that could measure the level of clubroot spores directly from soil. Plasmodiophora brassicae DNA was successfully extracted and amplified from artificially inoculated soils and from naturally infested field soils using real-time PCR with selected sets of primers and probes. Many different types of soil DNA extraction methods were tested and standard curves relating to different levels of spore inoculum were created. This project has generated useful information as to why there are contradictory results in clubroot research about the effect of various treatments at controlling clubroot. This information may also be the basis of practical advice to brassica growers on best practices to use to achieve optimal clubroot control in the field. Options in relation to new sustainable control treatments are discussed in the light of the results from both glasshouse and field experiments. These involve planting brassicas on raised beds and applying treatments strategically around the root zone. LimeX 70 or powdered calcium oxide were demonstrated to be the most optimal lime treatments for control, and a split application of Perlka (granular calcium cyanamide) may prove to be a consistently effective method for controlling clubroot.

Master of Science

One main goal of ecological research is to understand nature´s complexity, in order to predict the potential impact of environmental perturbations. In this thesis, I investigate the ecological interactions between some of the most ancient organisms living on our planet: plants and insects. Focus of my research is the interaction between the wild brassicaceous plant black mustard (Brassica nigra L.) and its specialist insect herbivore, the large white cabbage butterfly (Pieris brassicae L). Both organisms are well characterized model species used in chemical ecology research. Using different analytical techniques, such as liquid and gas chromatography coupled to mass-spectrometry (LC- and GC-MS) and headspace collection of volatile organic compounds (VOCs), I apply the approach of metabolomics and systems biology to the field of ecology to explore the metabolic changes occurring inside the plants exposed to biotic and abiotic stresses. Particularly, I study the plant metabolic responses against P. brassicae chewing caterpillars during sequential treatment exposure to: abiotic stress by the oxidative air pollutant ozone (O3); dual herbivory with specialist Brevicoryne brassicae piercing-sucking aphids; and chemical induction of plant defences with the oxylipin phytohormone methyl-jasmonate (MeJA). Results show how during herbivore-induced responses, changes in defence- and growth-metabolic processes are tightly connected to stress protection mechanisms, indicating that plants actively reprogram their inner metabolic networks in order to adapt to consecutive changes in the environment. This thesis illustrates how evaluating the plant metabolome in its entirety rather than single metabolites, can help us understanding plant responses towards abiotic and biotic stresses, and improve our ability to predict how constant shifts in the environment affect plant physiology and ecology. / Ett huvudsyfte för ekologisk forskning är att förstå naturens komplexitet för att kunna förutse effekter av störningar i miljön. I min avhandling har jag fokuserat på ekologiska interaktioner mellan växter och insekter, två av de äldsta terrestra organismgrupperna på jorden. I mina studier har jag undersökt interaktioner mellan den korsblommiga växten svartsenap (Brassica nigra L.) och den specifika herbivoren kålfjäril (Pieris brassicae L.). Båda är väl karaktäriserade modellarter i kemisk-ekologisk forskning. De metaboliska förändringar som sker när växten utsätts för biotisk och abiotisk stress har analyserats hjälp av metabolomik, det vill säga analyser av metabolomet i sin helhet med hjälp av tekniker som vätske- och gaskromatografi kopplad till masspektrometri (LC- och GC-MS), och så kallad headspace-uppsamling av flyktiga organiska föreningar (VOCs). Jag har särskilt undersökt de metaboliska förändringar som sker när växten betas av kålfjärilslarver vid samtidig exponering för: abiotisk stress i form av ozon (O3), en oxidativ luftförorening; ytterligare betning i form av stickande och sugande bladlus (Brevicoryne brassicae); tillsats av oxylipinfytohormon metyl-jasmonat (MeJA), ett ämne som inducerar växtens försvar. Resultaten visar att de metaboliska förändringar som sker i växten vid herbivori med konsekvenser för dess försvar och tillväxt är nära kopplade till de metaboliska förändringar som sker vid stress, vilket visar att växten kan fortlöpande och aktivt omprogrammera sina metaboliska nätverk för att anpassa sig till förändringar i miljön. Avhandlingen visar att genom att utvärdera växtmetabolomet i sin helhet, snarare än att studera enskilda metaboliter, vi kan få bättre förståelse för hur växter reagerar på olika former av stress och därmed också bidra till att vi kan göra förutsägelser för hur förändringar i miljön kan påverka växters fysiologi och ekologi.

Des études récentes ont montré que la variabilité de l’épigénome des plantes est un acteur important dans la réponse des plantes aux stress abiotiques et biotiques. La hernie, causée par le protiste Plasmodiophora brassicae, est une maladie racinaire majeure des Brassicaceae cultivées dont la résistance quantitative est considérée comme résultant principalement de la ségrégation de multiples allèles. L'objectif de ma thèse est d'établir s'il existe, chez Arabidopsis thaliana, une variabilité épigénétique héritable à l'origine de variations de la réponse à l’infection par la hernie. Pour répondre à cet objectif, une approche non ciblée d’épigénétique quantitative a été réalisée en utilisant la population épiRIL ddm1-2 x Col-0. Dix-sept QTL sous contrôle épigénétique (QTLépi), regroupés en 6 régions génomiques, ont ainsi été détectés, 5 d’entre eux étant sous la dépendance de la température.Finalement, deux régions identifiées comme impliquées dans la réponse à la hernie ont été caractérisées plus finement. La région du gène majeur de résistance à la hernie RPB1, qui colocalise avec 3 QTLépi, présente une variation génomique prépondérante dans les écotypes d’Arabidopsis potentiellement due à des mouvements d’éléments transposables. Le QTL Pb-At5.2 est sous le contrôle d’une épimutation régulant l’état de méthylation et l’expression de deux gènes NLR. Les résultats obtenus montrent que la résistance quantitative à la hernie est associée à des variations de la méthylation de l’ADN stables et héritables suggérant un modèle complexe de régulation de la résistance où la combinai / Recent studies have shown that plant epigenome variability is an important factor in plant response to abiotic and biotic stress. Clubroot caused by the protist Plasmodiophora brassicae is a major disease of Brassicaceae whose quantitative resistance is supposed to result from many allele segregation. The aim of my work is to understand if, in Arabidopsis thaliana, an inherited epigenetic variability can lead to variations in clubroot resistance. For that, an untargeted approach of quantitative epigenetics was carried out using the epiRIL population ddm1-2 x Col-0. Seventeen QTL under epigenetic control (QTLepi), clustered in 6 genomic regions, were detected, 5 of them being temperature-dependant.Finally, two regions previously identified as involved in clubroot response were finely studied. The region of the major clubroot resistance gene RPB1, which colocalizes with three QTLepi, shows major genomic variations in Arabidopsis ecotypes potentially due to movements of transposable elements. The QTL Pb-At5.2 is depending on one epimutation controlling the methylation state and the expression of two NLR genes. The results obtained demonstrate that the clubroot quantitative resistance is associated with inherited stable DNA methylation variations suggesting a complex model of resistance regulation where favourable alleles and epialleles association is necessary to obtain an optimal resistance.