Multiple introductions from multiple sources: invasion patterns for an important Eucalyptus leaf pathogen

Abstract

Many population studies on invasive plant pathogens are undertaken without knowing the center of origin of the pathogen. Most leaf pathogens of Eucalyptus originate in Australia and consequently with indigenous populations available, and it is possible to study the pathways of invasion. Teratosphaeria suttonii is a commonly occurring leaf pathogen of Eucalyptus species, naturally distributed in tropical and subtropical regions of eastern Australia where it is regarded as a minor pathogen infecting older leaves; however, repeated infections, especially in exotic plantations, can result in severe defoliation and tree deaths. Nine polymorphic microsatellite markers were used to assess the genetic structure of 11 populations of T. suttonii of which four where from within its native range in eastern Australia and the remaining seven from exotic Eucalyptus plantations. Indigenous populations exhibited high allele and haplotype diversity, predominantly clonal reproduction, high population differentiation, and low gene flow. The diversity of the invasive populations varied widely, but in general, the younger the plantation industry in a country or region, the lower the diversity of T. suttonii. Historical gene flow was from Australia, and while self‐recruitment was dominant in all populations, there was evidence for contemporary gene flow, with South Africa being the most common source and Uruguay the most common sink population. This points distinctly to human activities underlying long‐distance spread of this pathogen, and it highlights lessons to be learned regarding quarantine.

Human-Mediated Gene Flow Contributes to Metapopulation Genetic Structure of the Pathogenic Fungus Alternaria alternata from Potato

“…Higher genetic differentiation as a result of lower gene flow was observed within cropping regions than among cropping regions in the current study (Tables 3 , 4 ). Similar patterns of spatial population genetic structure have also been found in other agricultural plant pathogens (Rieux et al, 2013 ; Taole et al, 2015 ), suggesting they are not unique to A. alternata . These results are counter intuitive and cannot simply be explained by natural dispersal, which is expected to create higher genetic similarity (lower genetic differentiation) among geographically closer subpopulations.…”

Low genetic diversity and strong geographic structure in introduced populations of the Eucalyptus foliar pathogen Teratosphaeria destructans

“…epicoccoides and T . cryptica (Taole et al ., 2015; Burgess and Wingfield, 2017), in both their native and introduced ranges. This is also true for the putatively heterothallic T .…”

“…Considering that native populations of fungal pathogens evolve over time and are expected to be more genetically diverse (McDonald, 1997), our results suggest that the studied populations had been introduced into the countries where they were collected. Similarly, populations of other Eucalyptus leaf‐infecting Teratosphaeria species that have a known Australian origin had low genetic diversity in their introduced populations compared to their native origins (Pérez et al ., 2012; Taole et al ., 2015; Burgess and Wingfield, 2017). It is currently not known where T .…”

“…epicoccoides and T . zuluensis (Taole et al ., 2015; Aylward et al ., 2019). The genotypes within each of the populations from China, Thailand, and North and South Sumatra were closely related, suggesting that each population has evolved independently.…”

“…The results of this study are congruent with what is known for non‐native populations of other tree pathogens. These include Teratosphaeria leaf pathogens (Pérez et al ., 2012; Taole et al ., 2015; Burgess and Wingfield, 2017), exotic pine foliar pathogens such as Dothistroma septosporum and Lecanosticta acicola (Barnes et al ., 2014; Janoušek et al ., 2016), exotic Phytophthora alni subsp. uniformis populations in Europe causing alder decline (Aguayo et al ., 2013), and exotic Chrysoporthe cubensis on Eucalyptus in southern and eastern Africa (Nakabonge et al ., 2007).…”