Quantitative plant disease resistance is believed to be more durable than
qualitative resistance, since it exerts less selective pressure on the
pathogens. However, the process of progressive pathogen adaptation to
quantitative resistance is poorly understood, which makes it difficult to
predict its durability or to derive principles for its sustainable deployment.
Here, we study the dynamics of pathogen adaptation in response to quantitative
plant resistance affecting pathogen reproduction rate and its carrying
capacity. We developed a stochastic model for the continuous evolution of a
pathogen population within a quantitatively resistant host. We assumed that
pathogen can adapt to a host by the progressive restoration of reproduction
rate or of carrying capacity, or of both. Our model suggests that a combination
of QTLs affecting distinct pathogen traits was more durable if the evolution of
repressed traits was antagonistic. Otherwise, quantitative resistance that
depressed only pathogen reproduction was more durable. In order to decelerate
the progressive pathogen adaptation, QTLs that decrease the pathogen's ability
to extend must be combined with QTLs that decrease the spore production per
lesion or the infection efficiency or that increase the latent period. Our
theoretical framework can help breeders to develop principles for sustainable
deployment of quantitative trait loci.
