Pathways to Recovery: Genomics and Resistance Assays for Tree Species Devastated by the Myrtle Rust Pathogen

The latest collaborative paper from the lab is out in Molecular Ecology, with another great contribution from former PhD student Stephanie Chen. I really enjoyed collaborating with the team at the Royal Botanic Gardens and Domain Trust (and beyond), and this accomplishment feels like a fitting way to celebrate my first week as an ecological consultant at ORS. It combines reference genomes with population genomic data and resistance assays to provide hope in the fight against invasive pathogens - the notorious myrtle rust in this case - but with a warning: these species, like so many, have already suffered dramatic losses of genetic variation.

We have the tools and the knowledge to save biodiversity. We need the political will. And we don’t have the time to delay any further.

Chen SH, Yap YS, Viler V, Stehn C, Sandhu KS, Percival J, Pegg GS, Menzies T, Jones A, Guo K, Giblin FR, Cohen J, Edwards RJ, Rossetto M & Bragg JG (2025): Pathways to Recovery: Genomics and Resistance Assays for Tree Species Devastated by the Myrtle Rust Pathogen. Molecular Ecology e70030. [Mol Ecol] [PubMed] [bioRxiv]

Abstract

Myrtle rust is a plant disease caused by the invasive fungal pathogen Austropuccinia psidii (G. Winter) Beenken, which has a global host list of 480 species. It was detected in Australia in 2010 and has caused the rapid decline of native Myrtaceae species, including rainforest trees Rhodamnia rubescens (Benth.) Miq. (scrub turpentine) and Rhodomyrtus psidioides (G.Don) Benth. (native guava). Ex situ collections of these species have been established, with the goal of preserving remaining genetic variation. Analysis of reduced representation sequencing (DArTseq; n = 444 for R. rubescens and n = 301 for R. psidioides) showed genetic diversity is distributed along a latitudinal gradient across the range of each species. A panel of samples of each species (n = 27 for R. rubescens and n = 37 for R. psidioides) was resequenced at genome scale, revealing large historical effective population sizes, and little variation among individuals in inferred levels of deleterious load. In Rhodamnia rubescens, experimental assays (n = 297) identified individuals that are putatively resistant to myrtle rust. This highlights two important points: there are tangible pathways to recovery for species that are highly susceptible to rust via a genetically informed breeding programme, and there is a critical need to act quickly before more standing diversity is lost.