Evolutionary history of the conifer root rot fungus Heterobasidion annosum sensu lato

Abstract

We investigated two hypotheses for the origin of the root rot fungus Heterobasidion annosum species complex: (i) that geology has been an important factor for the speciation (ii) that co-evolutionary processes with the hosts drove the divergence of the pathogen species. The H. annosum species complex consists of five species: three occur in Europe, H. annosum s.s., Heterobasidion parviporum and Heterobasidion abietinum, and two in North America, Heterobasidion irregulare and Heterobasidion occidentale; all with different but partially overlapping host preferences. The evolution of the H. annosum species complex was studied using six partially sequenced genes, between 10 and 30 individuals of each species were analysed. Neighbour-joining trees were constructed for each gene, and a Bayesian tree was built for the combined data set. In addition, haplotype networks were constructed to illustrate the species relationships. For three of the genes, H. parviporum and H. abietinum share haplotypes supporting recent divergence and/or possible gene flow. We propose that the H. annosum species complex originated in Laurasia and that the H. annosum s.s./H. irregulare and H. parviporum/H. abietinum/H. occidentale ancestral species emerged between 45 and 60 Ma in the Palaearctic, well after the radiation of the host genera. Our data imply that H. irregulare and H. occidentale were colonizing North America via different routes. In conclusion, plate tectonics are likely to have been the main factor influencing Heterobasidion speciation and biogeography.

Accumulation of iron-binding compounds in root of Pinus sylvestris challenged by Heterobasidion annosum sensu lato

“…We also observed a greater accumulation of iron in P. sylvestris roots in response to exposure to H. annosum s.s. than in response to the other two species . Heterobasidion parviporum and H. abietinum are genetically related to each other more closely than to H. annosum s. s. (Karjalainen 1996;Kasuga et al 1993), which was confirmed by evolutionary studies by Dalman et al (2010). This can explain the similar response of the host to H. parviporum and H. abietinum.…”

Secondary metabolite comparison of the species within the Heterobasidion annosum s.l. complex

“…species complex has been studied using several different genetic markers (Garbelotto et al, 1996;Harrington et al, 1998;Kasuga and Mitchelson, 2000;Maijala, 2000;Johannesson and Stenlid, 2003;Linzer et al, 2008). (Dalman et al, 2010) proposed an evolutionary hypothesis for the H. annosum s.l. species complex where it originated in Laurasia and that the H. annosum s.s./H.…”

“…Migration and allopatric separation later lead to the development of the pine infecting species H. annosum s.s. and H. irregulare in Europe and North America, respectively. Although through a different migration route H. occidentale established and developed in North America while further separation in sympatry leads to the development of H. parviporum and H. abietinum in Europe which is reflected in the current species distribution (Dalman et al, 2010).…”

Heterobasidion annosum s.l. Genomics

“…Even though the different species have been separated for up to 75 million years (Dalman et al, 2010), they have retained a high degree of interfertility and a wide range of host species. This means potentially dire consequences if a species should be successfully introduced in a foreign environment.…”