Fungal diseases on crops, epidemics and adaptation: studies of transmission of the blackleg fungus on canola

Date

Tuesday 30 May 2017

Time

12:30-13:30 (AEST)

Venues

CSIRO: Black Mountain – Discovery Theatre, St Lucia QBP – Level 3 South telepresence room (3.323), Floreat – B1b Boardroom, Waite – B101-FG-R00-SmallWICWest

Speaker

Lydia Bousset, Research Scientist at The Institute of Genetics Environment and Plant Protection, INRA, France

Synopsis

In agro-ecosystems human actions result in the alternation of continuities and discontinuities over time and space, for example for the presence vs. absence of host crops, and this induces cyclic epidemics. Thus, the adaptation of pathogen populations to host resistances has to be studied at the scale of a network of fields on which the selection pressures are not homogeneous, during a succession of cropping seasons. Because epidemics of successive cropping seasons are not independent, modelling requires empirical data on inoculum production and dissemination from one cropping season to the next. Results from recent studies on dispersal, on inoculum production and field experiment will be presented. A new method to quantify plant disease severity was developed, based on counting of leaf spots observed during one minute in a delimitated one square meter area. With this method, we estimated the dispersal kernel of Leptosphaeria maculans ascospores from stubble left after harvest in the previous summer to newly sown oilseed rape fields, using stem canker autumn disease severity. Because spore dispersal depends on source strength, we then aimed at comparing the inoculum production potential from different fields. After disease severity assessment, stubble pieces were incubated over summer and used to inoculate field plots of a susceptible variety. We confirmed that the contrast in stem canker severity leads to a contrast in the contamination potential and tested for field effect. The numbers of fruiting bodies were estimated from their areas on digital pictures of stubble pieces, which required us to develop an image segmentation analysis and compare it to the existing methods. Finally, in collaboration with colleagues at CSIRO, we investigated whether field experiments can tell us something about epidemics in agricultural landscapes. Population size was estimated on plots inoculated with combinations of stubble from contrasting sources. The composition of resulting populations was studied by sampling individuals and phenotyping them for virulence. These data and methods open the prospect of refining the existing simulators, developing disease risk maps for the deployment of crops at the landscape scale, or comparing promising strategies in field experiment.

Biography

Lydia Bousset is epidemiologist at INRA since 2002. Trained as a biologist at the University Paris XI Orsay and engineer in agronomy, she did her PhD in epidemiology and post-docs in plant pathology at the University of Giessen (Germany) and population genetics at CNRS Montpellier (France). Since July 2016 she has been a McMaster fellow in the management of biotic threats group at CSIRO Canberra. Her research program is centred on the management of epidemics on crops, especially the adaptation of fungi to the use of genetic resistance in varieties when selection pressures imposed by human actions are heterogeneous over a network of fields.

This is a public seminar.

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