Canadian Forest Service Publications
Phylogenetic species recognition reveals host-specific lineages among poplar rust fungi. 2013. Vialle, A.; Feau, N.; Frey, P.; Bernier, L.; Hamelin, R.C. Mol. Phylogenet. Evol. 66:628-644.
Issued by: Laurentian Forestry Centre
Catalog ID: 34433
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Fungal species belonging to the genus Melampsora (Basidiomycota, Pucciniales) comprise rust pathogens that alternate between Salicaceae and other plant hosts. Species delineation and identification are difficult within this group due to the paucity of observable morphological features. Several Melampsora rusts are highly host specific and this feature has been used for identification at the species level. However, this criterion is not always reliable since different Melampsora rust species can overlap on one host but specialize on a different one. To date, two different species recognition methods are used to recognize and define species within the Melampsora genus: (i) morphological species recognition, which is based solely on morphological criteria; and (ii) ecological species recognition, which combines morphological criteria with host range to recognize and define species. In order to clarify species recognition within the Melampsora genus, we applied phylogenetic species recognition to Melampsora poplar rusts by conducting molecular phylogenetic analyses on 15 Melampsora taxa using six nuclear and mitochondrial loci. By assessing the genealogical concordance between phylogenies, we identified 12 lineages that evolved independently, corresponding to distinct phylogenetic species. All 12 lineages were concordant with host specialization, but only three belonged to strictly defined morphological species. The estimation of the species tree obtained with Bayesian concordance analysis highlighted a potential co-evolutionary history between Melampsora species and their reciprocal aecial host plants. Within the Melampsora speciation process, aecial host may have had a strong effect on ancestral evolution, whereas telial host specificity seems to have evolvedmore recently. Themorphological characters initially used to define species boundaries in the Melampsora genus are not reflective of the evolutionary and genetic relationships among poplar rusts. In order to construct a more meaningful taxonomy, host specificity must be considered an important criterion for delineating and describing species within the genus Melampsora as previously suggested by ecological species recognition.
Plain Language Summary
Fungal species belonging to the genus Melampsora are responsible for several diseases including poplar leaf rust, the most significant poplar disease in the world. However, it is difficult to accurately identify the various species of Melampsora because they have few distinctive morphological features.
Several Melampsora species need to alternate between the host plant (e.g. poplar) and an alternate plant (e.g. larch) to complete their life cycle and cause disease. In some cases, the identity of the alternate plant can be used to identify the species of Melampsora.
For better identification, the researchers compared the genetic fingerprint of different species of Melampsora. This work contributed to a better taxonomic description of these species, making identification and management of the diseases they cause much easier.