|Title:||Pathogens of cotton seedlings in NSW Australia|
|Publisher:||University of Sydney|
Faculty of Science.
|Abstract:||This study aimed to further expand understanding of the pathogens of cotton seedlings across NSW, and to identify pathogens associated with increased seedling mortality in southern NSW. A total of 230 organisms were recovered into pure culture from 192 locations and most screened for pathogenicity. The genera Rhizoctonia, Pythium, Fusarium, Macrophomina, and Sclerotium were isolated from diseased tissues and pathogens included R. solani anastomosis group (AG) 2-1, 2-2 IIIB, 3, 4 HG-I and 4 HG-III, Pythium sp., P. ultimum, P. helicoides and S. rolfsii. Pathogenicity of R. solani AG 3 and P. helicoides against cotton is novel. Pathogenic Pythium spp. were more commonly associated with samples from southern NSW. There was no variation in aggressiveness between isolates of Pythium from northern and southern regions, and pesticide controlled pathogen growth on amended agar and seedling disease in pots. The aggressiveness of Pythium spp. towards cotton was increased under temperatures reflective of Griffith NSW indicating that cool temperatures are probably the main driver behind increased aggressiveness of Pythium spp. and may account for historically high levels of seedling death in the south. Isolates of P. helicoides were insensitive to metalaxyl-M on pesticide amended agar and when exposed to pesticide seed treatment and caused root rot. Among AGs of R. solani, isolates of AG 4 HG III grew fastest among isolates at 30°C, whilst isolates of AG 4 HG I were most aggressive at all temperatures. Isolates of AG 2-1 displayed an intermediate level of aggressiveness and insensitivity to azoxystrobin. Isolates of AG 2-2 IIIB and AG 3 caused the lowest levels of disease among isolates. A distinct clade was identified among AG 3 ITS sequences belonging to isolates from cotton in Australia. AG 3 isolates from cotton caused disease on cotton seedlings but not on potato suggesting support for the phylogenetic specialisation of AG 3 on cotton or the Malvaceae in Australia.|
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|Rights and Permissions:||The author retains copyright of this thesis. It may only be used for the purposes of research and study. It must not be used for any other purposes and may not be transmitted or shared with others without prior permission.|
|Type of Work:||PhD Doctorate|
|Type of Publication:||Doctor of Philosophy Ph.D.|
|Appears in Collections:||Sydney Digital Theses (University of Sydney Access only)|
|2015_Christopher_Anderson_Thesis.pdf||PhD Thesis||7.76 MB||Adobe PDF|
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