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Thesis started january 1st, 2020 - Defended december 16th, 2022
Funding: Dpt SPE Région Bretagne
Direction: Frédéric Hamelin, Didier Andrivon, Ludovic Mailleret​

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Abstract:

Allowing growers to get free from pesticide use and preserving cultivated genetic resources while limiting the emergence of new diseases is one of the aims of the ongoing agroecological transition. To these ends, cultivar mixtures are an effective and more sustainable solution than pure stands of resistant cultivars, but a lack of understanding persists about how they work. Plant immunity and more specifically immune priming is sometimes mentioned to explain the observed efficiency of mixtures, but its mode of action on epidemics is still poorly known. I thus developed epidemiological models to identify the effects of priming on the effectiveness of mixtures. These models evidence that priming is critical to explain the observed effectiveness of cultivar mixtures. In a mixture of susceptible and resistant cultivars, priming decreases disease prevalence compared to a pure stand of the resistant host. In a mixture of resistant cultivars, priming also reduces the number or resistance genes needed to maintain disease prevalence below an acceptable threshold. In addition, the models make it possible to evaluate in what proportions cultivars should be mixed to optimize mixture efficiency and increase the durability of the resistances used. The variety to be mixed in the greatest proportion is the one that is the least costly for the pathogen to break. These novel theoretical contributions, sometimes counter intuitive but explainable ecologically, highlight how individual immunity scales up at the population level, and encourage future research to best exploit priming in plant protection strategies.

Poster pdf