The genetic structure of the plant pathogenic fungus Melampsora larici-populina on its wild host is extensively impacted by host domestication

Abstract

Wild and cultivated plants represent very different habitats for pathogens, especially when cultivated plants bear qualitative resistance genes. Here, we investigated to what extent the population genetic structure of a plant pathogenic fungus collected on its wild host can be impacted by the deployment of resistant cultivars. We studied one of the main poplar diseases, poplar rust, caused by the fungus Melampsora larici-populina. A thousand and fifty individuals sampled from several locations in France were phenotyped for their virulence profile (ability to infect or not the most deployed resistant cultivar 'Beaupré'), and a subset of these was genotyped using 25 microsatellite markers. Bayesian assignment tests on genetic data clustered the 476 genotyped individuals into three genetic groups. Group 1 gathered most virulent individuals and displayed evidence for selection and drastic demographic changes resulting from breakdown of the poplar cultivar 'Beaupré'. Group 2 comprised individuals corresponding to ancestral populations of M. larici-populina naturally occurring in the native range. Group 3 displayed the hallmarks of strict asexual reproduction, which has never previously been demonstrated in this species. We discuss how poplar cultivation has influenced the spatial and genetic structure of this plant pathogenic fungus, and has led to the spread of virulence alleles (gene swamping) in M. larici-populina populations evolving on the wild host.

Molecular characterization of a Hog1-type MAPK, MlpHog1, from Melampsora larici-populina

“…Conversely, the sexual stage of this rust fungus occurs on larch needles (Larix sp.) in spring (Xhaard et al 2011), persisting for a long time from the vegetative stage to the sexual stage. Additional work is required to explore the function of the MlpHog1 gene during the sexual stage.…”

Molecular evidence indicates that subarctic willow communities in Scotland support a diversity of host-associated Melampsora rust taxa

“…One hypothesis to account for this subclade is that it represents a newly evolved taxon, derived from M. epitea, which is specifically adapted to S. lapponum, S. myrsinites, and their hybrids and therefore has high virulence on them. Such a new taxon may have a lower diversity than the taxon from which it has been derived because it has passed through a bottleneck during the process of adapting to the restricted set of hosts (Xhaard et al 2011). This hypothesis predicts that infection levels on S. lanata, and the Salix species to which the subclade is adapted, should be decoupled.…”

Variation in resistance to the rust fungus Melampsora larici-populina Kleb. in Populus nigra L. in the Czech Republic

“…Pinon & Frey (1997) reported the main selection force exerted on rust populations was host population. However, Xhaard et al (2011) showed poplar cultivation influenced spatial distribution and genetic structure of the fungal plant pathogen and resulted in the spread of a range of different virulence alleles in most pathogen populations.…”