Highly clonal structure and abundance of one haplotype characterize the
Diplodia sapinea populations in Europe and western Asia
Diplodia sapinea is a cosmopolitan endophyte and opportunistic pathogen
occurring on several conifer species in Europe for at least 200 years.
In Europe, disease outbreaks have increased on several Pinus spp. in the
last few decades. In this study, the genetic structure of the European
D. sapinea population was investigated using thirteen microsatellite
markers. In total, 425 isolates from 15 countries were analysed. A high
clonal fraction and low genetic distance between most populations was
found. One single haplotype dominates the European population, being
represented by 44% of all isolates and found in nearly all investigated
countries. Three genetically distinct subpopulations were found:
Central/North European, Italian and Georgian. The recently detected
populations of D. sapinea in northern Europe (Latvia, Estonia and
Finland) share several haplotypes with the German population, suggesting
introduction from Central Europe. The northern European populations show
similar genetic diversity to those in Central Europe suggesting either
that the fungus has existed in the North in an asymptomatic mode for a
long time or that it has spread recently by multiple introductions.
Although this fungus reproduces predominantly asexually, considerable
genetic diversity was found even among isolates of a single tree.
According to currently published allelic patterns, D. sapinea most
likely originates from North America. In order to enable the detection
of endophytic or latent infections of planting stock by D. sapinea, new
species-specific PCR primers were designed. During the search for
Diplodia isolates, we identified D. africana in California, USA, which
is the first record of this species in North America.