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PhD Position - Evaluating fungicide anti-resistance strategies by the mean of experimental evolution: the case of Zymoseptoria tritici, the causal agent of septoria leaf blotch

PhD Position - Evaluating fungicide anti-resistance strategies by the mean of experimental evolution: the case of Zymoseptoria tritici, the causal agent of septoria leaf blotch

INRA, France

 

Working environment

Context

Modern fungicides contribute to world agricultural production but their sustainability is threatened by the widespread evolution of fungicide resistant plant pathogens. A major challenge for crop protection is to enhance the sustainability of the available molecules while reducing and optimizing their use. Resistance prevention and management rely on the introduction of alternative methods as well as on the skillful deployment of molecules over time and space, at an appropriate dose. Nevertheless, the scientific community is divided upon the respective efficacy of the various strategies –namely alternation, mosaic, mixture and dose modulation- to delay resistance emergence and spread. The sustainability of anti-resistance strategies has been explored from empirical data and mostly by modelling but both approaches failed in giving a definite position in this debate, probably because the interest of strategies may differ according to the biology of the organism and the genetics of resistance. Resistance can be conferred by mutations that result in structural changes of the fungicide target enzyme (target site resistance), resulting in specialist resistance to a single class of fungicides. Alternatively, non-target site resistance can lead to specialist or generalist resistance phenotypes. Generalist phenotypes may display unpredictable resistance to multiple unrelated classes of fungicides. Moreover these various resistance mechanisms require different resource investment and thus may be associated with contrasted fitness penalties. Resistance evolution then results from the trade-off between positive selection driven by fungicides and negative selection,i.e.fitness penalty. Therefore, without a fine knowledge of the responses to selection by fungicide applications, it will not be possible to predict or manipulate (viaappropriate anti-resistance strategies) the evolutionary behavior of pesticide resistance genes or phenotypes.

Zymoseptoria triticiis the causal agent septoria leaf blotch and the most detrimental fungal pathogen of wheat. In Western Europe, it has evolved resistance in the field to all current unisite inhibitors, leading to contrasted efficacy losses, according to the modes of action, and new means to control this pathogen are desperately needed. These resistances may be caused either by target  or non target site mechanisms. This pathogen can be easily handled in laboratory due to its yeast-like form and many biological or molecular tools are available to quantify the various resistant genotypes. All these reasons makeZ. tritician excellent model to study resistance management, by the mean of experimental evolution.

Objectives and strategy

In the context described above, this project aims to answer the following questions:

“What are the drivers ofZ. tricitiresistance selection?

How to use them to enhance the sustainability of anti-resistance strategies in Z. tritici?”

Clearly, in this project, we are primarily interested in the mode of fungicide selection (i.e.in the selection patterns and dynamics delaying or accelerating resistance evolution), to assess the efficacy of anti-resistance strategies and to bring new components in the debate described previously, while using an experimental evolution approach, an original tool for fungi.

Experimental evolution tends to accelerate in lab-standardized and miniaturized conditions the natural selection driven by fungicides in the field. It is clearly an untapped resource to infer evolutionary histories and theories in fungi (Fisher & Lang 2016). In microbes, experimental evolution is usually used to assess the resistance risk of

fungicides or antibiotics via the further characterization of evolved mutants (mainly, resistance mechanisms and fitness). Here, we propose to use experimental evolution to compare anti-resistance strategies in standard conditions and to estimate selection coefficients through population dynamics modelling.

 

More information to be found here

Location: 
INRA, FR
Deadline: 
05/09/2017

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