Rust disease of eucalypts, caused by P uccinia psidii , did not originate via host jump from guava in B razil

The rust fungus, P uccinia psidii , is a devastating pathogen of introduced eucalypts ( E ucalyptus spp.) in Brazil where it was first observed in 1912. This pathogen is hypothesized to be endemic to S outh and C entral A merica and to have first infected eucalypts via a host jump from native guava ( P sidium guajava ). Ten microsatellite markers were used to genotype 148 P . psidii samples from eucalypts and guava plus five additional myrtaceous hosts across a wide geographic range of south‐eastern Brazil and Uruguay. Principal coordinates analysis, a B ayesian clustering analysis and a minimum‐spanning network revealed two major genetic clusters among the sampled isolates, one associated with guava and another associated with eucalypts and three additional hosts. M ultilocus genotypes infecting guava differed by multiple mutational steps at eight loci compared with those infecting eucalypts. Approximate B ayesian computation revealed that evolutionary scenarios involving a coalescence event between guava‐ and eucalypt‐associated pathogen populations within the past 1000 years are highly unlikely. None of the analyses supported the hypothesis that eucalypt‐infecting P . psidii in Brazil originated via host jump from guava following the introduction of eucalypts to Brazil approximately 185 years ago. The existence of host‐associated biotypes of P . psidii in Brazil indicates that this diversity must be considered when assessing the invasive threat posed by this pathogen to myrtaceous hosts worldwide.