Blueprints for field level IPM strategies and spatial designs for resistant genotype deployment

Durable resistance to plant pathogens is highly desired but hard to achieve because the use of plant resistance selects for pathogen genotypes that break resistance. The effectiveness of resistance genes is therefore often short-lived, and breeders have to continually adapt varieties to challenges by novel genotypes of pathogens. We explore the effect of resistance gene deployment strategies and pathogen life-cycle components on the useful life of resistance genes, and search of management strategies that can prolong the useful life of plant resistance. Gene deployment strategies include sequential use of varieties with single resistance genes, stacking of resistance genes within one variety, simultaneous planting of multiple varieties with a single resistance gene, and a mixed strategy that combines the use of a variety with stacked resistance genes and varieties with single resistance genes. We developed two models at two scales: a regional scale and a national scale. The regional model takes the effects of spatial design into account in a difference equation framework that is mathematically transparent and efficient in terms of data requirements and calculation time. The second model simulates the spread of genotypes of yellow rust in France over time, using a spatially explicit integro-difference equation model. Both models were used to develop blueprints for spatial strategies of resistance gene deployment. These blueprints consist of variety choice and characteristics of spatial deployment, i.e. fraction of resistant fields and degree of clustering of wheat fields. In the general discussion, we propose additional characteristics of spatial deployment strategies that we plan to test in the coming year.

The model results indicate that, when a small fraction of virulent pathogens is already present in the environment, the useful life of a variety with pyramided resistance genes is longer than the useful life of a variety with a single resistance gene. However, both the spatial implicit model at the regional scale and the spatial explicit model at national scale indicate that the useful life of a pyramid is not always longer than twice the useful life of a single resistance gene. In general, the regional model showed that the useful life of a resistant variety is shortened if the pathogen has a greater number of generation per growing season of its host, or if a larger proportion of spores disperse between fields. Both models show that the useful life of a resistant variety is shorter at a higher proportion of resistant fields. The regional model analyses indicate that without fitness penalties for pathogen virulence, plant resistance cannot be made permanent. Nevertheless, deployment strategy can modify the durable life considerably.

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The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/ 2007-2013) under the grant agreement n°265865- PURE