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.