Is there a trade-off betwenn aggressiveness and overwinter survival in Phytophthora infestans ?

International audience1. Selection during interepidemic stages is crucial for the evolution of pathogen populations. Trade-offs involving aggressiveness (quantitative pathogenicity) have rarely been explored in pathogens with a life cycle requiring the disease-causing organism to change organs within the same host.2. We investigated the existence of a trade-off between aggressiveness and survival in Phytophthora infestans, the pathogen causing potato late blight. In France, P. infestans behaves as an obligate biotroph, surviving in infected tubers. Aggressive isolates, which are favoured during the epidemic, may exhaust their nutrient supply too quickly to bridge seasons, resulting in a possible trade-off between the two life stages.3. We inoculated tubers with isolates possessing different aggressiveness levels, let them overwinter as outdoor piles at three different sites, and scored the proportion of live tubers the following spring.4. At two sites, infection caused early tuber sprouting, which can be seen either as a manipulation of the host by the pathogen, or as an attempt by the host to escape.5. Overwinter survival was higher for control than for inoculated tubers, but did not differ between tubers inoculated with different isolates. This suggests that aggressiveness should gradually increase in P. infestans populations, unless a trade-off occurs at another stage of the life cycl