Molecular analyses identify hybridization-mediated nuclear evolution in newly discovered fungal hybrids.

Hybridization may be a major driver in the evolution of plant pathogens. In a high elevation Alpine larch stand in Montana, a novel hybrid fungal pathogen of trees originating from the mating of with has been recently discovered. In this study, sequence analyses of one mitochondrial and four nuclear loci from 11 genotypes collected in the same Alpine larch stand indicated that hybridization has increased allelic diversity by generating novel polymorphisms unreported in either parental species. Sequence data and ploidy analysis through flow cytometry confirmed that heterokaryotic ( + ) genotypes were not first-generation hybrids, but were the result of multiple backcrosses, indicating hybrids are fertile. Additionally, all admixed genotypes possessed the mitochondrion, indicating that the hybrid progeny may have been backcrossing mostly with . Based on reticulate phylogenetic network analysis by PhyloNet, Bayesian assignment, and ordination tests, alleles can be defined as -like or -like. -like alleles are clearly distinct from all known alleles and are derived from the admixing of both species. Instead, all but one alleles found in hybrids, although novel, were not clearly distinct from alleles found in the parental population. This discovery demonstrates that Alpine larch can be a universal host favouring the interspecific hybridization between and and the hybridization-mediated evolution of a nucleus, derived from parental species but clearly distinct from it.