Spatial invasion by a virulent pathogen: successive breakdowns of different resistant hosts
N. Sapoukhina (1), P. Gladieux (1), H. L. Pedersen (2), B. Le Cam (1)
(1) UMR PaVé, Centre INRA d'Angers, Rue Georges Morel, BP 57, 49071 Beaucouzé Cedex
(2) Department of Horticulture, Research Centre Aarslev, Kirstinebjergvej 10, DK-5792 Arslev, DENMARK
One of the control strategies of fungal crop diseases is planting highly resistant varieties. However selection pressure on the pathogen, imposed by major resistance genes, leads to the development of new virulent races. In most cases breakdown of resistance were reported for crop-pathogen systems with a genetically uniform crop distributed over large areas. Recently, the cases of pathogen invasion by adaptation to different resistant host-genotypes were manifested. Thus, there is a need to derive new strategies of breeding and spatial deployment of resistant cultivars, which would lead to durable resistance. To attain this goal we developed a dynamical model for the evolution of pathogen virulence under a multilocus gene-for-gene interaction with hosts in a two dimensional habitat. The model was verified by applying to the epidemic development of apple scab, caused by the fungus Venturia inaequalis, in Denmark. We used a population genetic approach to identify which of traits (mutation, recombination, migration) were significant in the process of successive breakdowns of resistant hosts carrying different major resistance genes and their pyramids. Finally we focused on studying the role of recombination of pathogen genotypes and their spread. Combination of population dynamics and genetics, providing an explicit simulation of the spatial patterns of disease propagation, allows us to test different hypothesis concerning prevention of the invasion of a virulent pathogen strain. In particular, we can compare the efficacy of host-heterogeneity introduced to the pathosystem at the genetic or population level. What is better to pyramid several resistance genes into a single cultivar or to plant mixtures of cultivars with different resistance genes? Do optimal planting patterns exist or not? The effective long-term strategies against pathogens are discussed. The authors would like to thank Charles-Eric Durel and Christian Lannou for comments and fruitful discussions.