Montarry, Josselin;  Corbière, Roselyne;  Glais, Isabelle; Pellé, Roland; Ellissèche, Daniel; Andrivon, Didier*. Pathogenicity, survival and transmission over seasons of Phytophthora infestans isolates. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-41.

From a pathologist’s point of view, the durable management of plant resistance to diseases can basically be regarded as a problem in evolutionary biology, since the durability of a plant resistance in an agroecosystem is a measure of the rate of adaptation of pathogen populations to the selection exerted by the host. This rate depends primarily on selective responses (occurring for annual plants during the epidemic phase, and in obligate pathogens also in the survival stages), but also on the balance between selection and diversifying processes (mutation, recombination, gene flow) on one hand, and between selection and genetic drift on the other hand. It is therefore crucial to take both the epidemic and survival stages of the pathogen’s life cycle into account to properly assess adaptation rates and patterns. Using the potato / Phytophthora infestans pathosystem, we showed 1) general adaptation of the pathogen to the locally prevalent cultivars, irrespective of their resistance, 2) selection for increased aggressiveness during the course of local epidemics, and 3) an absence of trade-off between aggressiveness during epidemics and survival ability in infected tubers. We also showed that infection by P. infestans induced earlier sprouting of tubers, suggesting either a host manipulation by the pathogen in order to reduce the length of survival periods into tubers or a response of the host to infection in order to minimise lethality. Our findings support the view that asexual P. infestans populations consist of single specialist genotypes adapted to locally prevalent hosts; the resulting pattern of general adaptation to widespread cultivars should result in a continuous increase of aggressiveness levels over time, unless trade-offs occur between pathogenicity and other life-history traits and diversification of resistance sources (both for major genes and quantitative resistance) in time and space is used.

Keywords: Adaptation, host resistance, aggressiveness, survival, trade-off

*Institution: INRA

Email: Didier.Andrivon@rennes.inra.fr