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Understanding pathogen and environmental drivers of white leaf spot (Pseudocercosporella capsellae) epidemics and their impacts on canola

Tamsal Murtza: School of Agriculture and Environment Faculty of Science The University of Western Australia

<div>White leaf spot (<em>Pseudocercosporella capsellae</em>) is an important but underestimated disease worldwide on both oilseed and horticultural Brassicas. Canola (<em>Brassica napus)</em> most important oilseed <em>Brassica</em> crop worldwide and in Australia this white leaf spot results in losses up to 30%, especially in highly susceptible varieties. Australia is facing variable and increasing temperatures, elevated drought stress and increasingly unpredictable rainfall that together have been associated with shifts in virulence and increased diversity within the <em>P. capsellae</em> population. Australia-wide populations of <em>P. capsellae </em>are being studied in relation to their pathogenicity and virulence across different canola genotypes using a cotyledon based screening assay and also assessed for their genetic differences. Increased variability in climate has also been associated with increasing incidence and severity of white leaf spot, likely due to more favourable conditions for development of severe epidemics. The variable Mediterranean climate in south west Western Australia makes it an ideal location to study and model current and future climate effects, and to project future risks, of white leaf spot epidemics on canola. Studies are being undertaken to define the key environmental drivers of white leaf spot epidemics. Significant phenotypic and genetic variation has been identified within the <em>P. capsellae</em> population and this is helping to explain the increasing importance and adverse impact of white leaf spot over recent decades.</div>