Abstract:
Human-associated introduction of pathogens and consequent invasions is very evident
in areas where no related organisms existed before. In areas where related but distinct
populations or closely related cryptic species already exist, the invasion process is
much harder to unravel. In this study, the population structure of the Eucalyptus leaf
pathogen Teratosphaeria nubilosa was studied within its native range in Australia,
including both commercial plantations and native forests. A collection of 521 isolates
from across its distribution was characterized using eight microsatellite loci, resulting
in 112 multilocus haplotypes (MLHs). Multivariate and Bayesian analyses of the
population conducted in STRUCTURE revealed three genetically isolated groups (A, B
and C), with no evidence for recombination or hybridization among groups, even
when they co-occur in the same plantation. DNA sequence data of the ITS (n = 32),
b-tubulin (n = 32) and 27 anonymous loci (n = 16) were consistent with microsatellite
data in suggesting that T. nubilosa should be considered as a species complex.
Patterns of genetic diversity provided evidence of biological invasions by the
pathogen within Australia in the states of Western Australia and New South Wales
and helped unravel the pattern of invasion beyond Australia into New Zealand, Brazil
and Uruguay. No significant genetic differences in pathogen populations collected in
native forests and commercial plantations were observed. This emphasizes the
importance of sanitation in the acquisition of nursery stock for the establishment of
commercial plantations.
