The fungus responsible for the downy mildew disease, common on commercially grown sunflowers, is Plasmopara halstedii (Farlow) Berl. et de Toni, one of the Peronosporaceae in the Oomycetes, known to be soil borne and to infect via the roots. [...]

No description available.

<I>Phytophthora cinnamomi </I>var. <I>cinnamomi, Pythium ultimum </I>var. <I>ultimum </I>and <I>Pythium undulatum </I>were successfully isolated from naturally regenerating <I>Pinus sylvestris </I>forests across north Scotland. Molecular and morphological characterisation enabled accurate identification of these Oomycetes to the variety level. <I>In vitro</I> and glasshouse pathogenicity trials demonstrated that under artificial temperature, light and water regimes the Oomycetes had the potential to reduce plant growth and cause chlorosis of the <I>P. sylvestris</I> foliage after two months. Soil pH was also determined as having a significant effect on <I>P. sylvestris </I>growth in terms of foliage colour and dry mass. Biological control <I>in vitro </I>experiments with <I>Bacillus subtilis</I> and <I>Pseudomonas fluorescens</I> produced significant inhibition of Oomycete growth but on transfer to the glasshouse trials, antagonism was not observed. This study was undertaken to establish the presence of fine root pathogens, namely those belonging to the Oomycetes, within regenerating <I>Pinus sylvestris</I> forests in northern Scotland. The identify of the pathogens was determined using morphological and molecular biology techniques. The virulence of the fine root pathogens on <I>Pinus sylvestris </I>seedlings (1 + 0) was then determined by a series of <I>in vitro</I> and glasshouse trials. Interactions between soil pH and bacterial biological control agents were also tested against each of the pathogens. Pathogen trials were undertaken to show the potential effect of the Oomycetes on <I>Pinus sylvestris </I>seedlings. The glass house trial was scored on foliage colour and dry weight of seedlings 18 months of age, grown in pH amended Irish moss peat. In comparison to the control, inoculation with <I>P. cinnamomi</I> caused a significantly greater frequency of chlorotic/dead seedlings. In contrast, inoculation with <I>P. undulatum </I>(syn. <I>P. dimorphum</I>) resulted in a greater number of healthy seedlings than the control. No significant difference in the proportion of healthy and chlorotic/dead seedlings was found between the bio-control bacteria groups. pH was found to have a significant effect on seedling growth. At pH 7, compared to pH 3, there was a significant greater likelihood of the seedlings being chlorotic/dead.

No description available.

Downy mildew, caused by the biotrophic Oomycete Plasmopara viticola, is one of the most important diseases of grapevines world wide. It is particularly destructive in temperate viticultural regions that experience warm wet conditions during the vegetative growth of the vine (Wong et al., 2001). The disease is not normally a problem in mediterranean climates where the growing season tends to be hot and dry (Mullins et al., 1992; Sivasithamparam, 1993). Grape downy mildew is however a major disease in Australian viticulture (McLean et al., 1984; Magarey et al., 1991). Grape downy mildew was first reported in Europe in 1878 (Viennot-Bourgin, 1981). In Australia, it was recorded for the first time in 1917 at Rutherglen in Victoria (Vic) (de Castella, 1917). The first recorded outbreak of the disease in Western Australia (WA) occurred in 1997 in a small planting of vines in the far north of the state. In the subsequent year, it was detected in widespread commercial viticulture in the Swan Valley production area, near Perth (McKirdy et al., 1999). The pathogen has since been found in all grape growing regions of WA. Since its introduction into European vineyards in the 1880?s, P. viticola has become one of the world?s most investigated grapevine pathogens. Many aspects its basic biology however remain unknown (Wong et al., 2001). Due to the recent detection of P. viticola in WA, little is known of the nature of strains of the pathogen in the state and their response to local environmental conditions. Much of the research concerning the influence of environmental factors on the development of P. viticola has been conducted in Europe e.g. parts of France and Germany. Due to significant differences in climatic conditions and a shorter selection time on the pathogen in WA, much of the information described in European studies may not be directly applicable to the grape downy mildew disease situation in WA. The focus of this thesis was to examine epidemiological aspects of P. viticola in the mediterranean climate of WA. The environmental conditions that could favour the development of epidemics by strains of the pathogen that have been detected in the state were determined. The existence of P. viticola ecotypes and genetic variation among strains from WA and the Eastern states of Australia was also investigated.

Thesis (Ph. D.)--University of Adelaide, 1986. / Includes bibliographical references (leaves 173-200).

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Thomas A. Evans, Dept. of Plant & Soil Sciences. Includes bibliographical references.

Thesis (M.S.)--Missouri State University, 2009. / "May 2009." Includes bibliographical references (leaves 44-50). Also available online.

Thesis (M.S.)--Oregon State University, 2005. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.