Genetic diversity of Teratosphaeria pseudoeucalypti in Eucalyptus plantations in Australia and Uruguay

Teratosphaeria pseudoeucalypti is a fungal pathogen that causes a severe leaf blight disease on Eucalyptus trees. While presumed to be native to Australia, T. pseudoeucalypti has become well established and an important constraint to forestry in South America. The aim of this study was to use microsatellite markers to investigate the genetic diversity of T. pseudoeucalypti outbreaks occurring in plantations in two distinct environments. In the New South Wales (NSW) plantation in Australia, a hybrid of two native Eucalyptus species was planted outside of its natural environment. In contrast, the plantations in Uruguay were of a non-native Eucalyptus species. Sixteen polymorphic microsatellite loci, identified in two genomes of T. pseudoeucalypti, were used to genotype 36 individuals from the NSW plantation and 21 were collected from across Uruguay. Genetic diversity in the NSW population was low (Hexp = 0.05), comprising five genotypes of which one occurred in > 80% of individuals. Despite high clonality and one MAT1-1 isolate among many MAT1-2 isolates, different genotypes co-occurred on a single tree and the hypothesis of recombination was not rejected. The diversity in the NSW plantation was consistent with that of an introduced pathogen, either from the surrounding native forests, or supporting earlier findings that T. pseudoeucalypti has only recently established in NSW. All isolates from Uruguay were clonal, harbouring the MAT1-1 idiomorph and a genotype distinct from those in Australia. This clonality suggests a single introduction of T. pseudoeucalypti into that country.