Résumé
Historical fluctuations in forests' distribution driven by past
climate changes and anthropogenic activities can have large impacts on the
demographic history of pathogens that have a long co-evolution history
with these host trees. Using a population genetic approach, we
investigated that hypothesis by reconstructing the demographic history of
Armillaria ostoyae, one of the major pathogens of the maritime pine (Pinus
pinaster), in the largest monospecific pine planted forest in Europe
(south-western France). Genetic structure analyses and approximate
Bayesian computation approaches revealed that a single pathogen population
underwent a severe reduction in effective size (12 times lower) 1080-2080
generations ago, followed by an expansion (4 times higher) during the last
4 generations. These results are consistent with the history of the
maritime pine forest in the region characterized by a strong recession
during the last glaciation (~19 000 years ago) and massive plantations
during the second half of the nineteenth century. Results suggest that
recent and intensive plantations of a host tree population have offered
the opportunity for a rapid spread and adaptation of their pathogens.