Abstract:
Many fungi in the Ophiostomatales are vectored by bark beetles that introduce these
fungi directly into their tree hosts. Most of these fungal associates have little effect on
their hosts, but some can cause serious diseases. One such fungus, Leptographium
wageneri, causes an economically and ecologically important tree disease known
as black stain root disease (BSRD). For this study, 159 full genome sequences of
L. wageneri were analyzed using a population genomics approach to investigate
the epidemiology, dispersal capabilities, and reproductive biology of this fungus.
Analyses were performed with SNP haplotypes from 155 isolates of L. wageneri var.
pseudotsugae collected in 16 Douglas-fir stands in Oregon and 4 isolates of L. wageneri
var. wageneri collected in pinyon pine stands in southern California. These two hostspecific
varieties appear to be evolutionarily divergent, likely due a combination of
factors such as host differentiation and geographic isolation. We analyzed gene flow
and population structure within and among Douglas-fir plantations in western Oregon to
infer the relative importance of local vs. long distance dispersal in structuring populations
of L. wageneri var. pseudotsugae. Long-distance gene flow has occurred between
Douglas-fir plantations, contributing to diversity and population structure within stands,
and likely reflecting the behavior of an important insect vector. Genetic clustering
analyses revealed the presence of unique local clusters within stands and plantations in
addition to those common among multiple stands or plantations. Although populations
of L. wageneri var. pseudotsugae are primarily asexual, two mating types were present
in many stands, suggesting that recombination is at least possible and may contribute
to genetic diversity.
