Barrès, Benoît; Halkett, Fabien*; Andrieux, Axelle; Pinon, Jean; Frey, Pascal. Population genetic structure of the poplar rust fungus Melampsora larici-populina at different spatial scales. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-20.
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Poplar cultivation in Europe is highly intensive and there have been many efforts by breeders during the past decades for developing cultivars with a good level of resistance to diseases. However, the Eurasian poplar rust fungus, Melampsora larici-populina, successively broke down all the complete resistances deployed so far in poplar cultivation, causing severe economic losses. Alternative strategies based on spatial management of available resistances and on breeding for partial resistance are on-going, but they need a good knowledge of the adaptation potential of the pathogen. Biological characteristics, such as the dispersal distances or the relative importance of sexual vs. asexual reproduction, are often difficult to measure for such phytopathogenic fungi. A way to infer these characteristics is the use of molecular markers. Fifteen microsatellite markers were developed in order to perform population genetics studies of M. larici-populina at different spatial scales. At a fine scale (lesion, leaf, twig, tree, site) a great genotypic diversity was observed, as well as a significant structure at the site and tree scales. At a regional scale, the study of M. larici-populina populations in the Durance River valley corridor revealed the co-occurrence of two epidemics, originating from two primary inoculum sources in the wild and in the cultivated compartments. Furthermore, gene flow from cultivated stands to wild stands was shown. The long distance migration capacity of M. larici-populina was assessed by studying eight European populations and two populations recently founded in Iceland and Canada. European populations exhibited an isolation by distance pattern, whereas non-European populations appeared to result from a strong founder effect with a long distance dispersal of a limited number of individuals. These results will be discussed in the perspective of breeding poplar for durable resistance.

Keywords: genetic diversity, isolation by distance, long distance dispersal, founder effect, epidemiology, gene flow, microsatellites.

*Institution: INRA, Nancy, France

Email: frey@nancy.inra.fr