Foliar fungal diversity related to Myrtle rust (Austropuccinia psidii) antagonism and its implications for pathogen resistance in the endangered Hawaiian Nioi (Eugenia koolauensis)

Abstract

An introduced fungal rust pathogen, Austropuccinia psidii, is a primary component contributing to the decline of the critically endangered Hawaiian Eugenia tree (Eugenia koolauensis). Once common on the islands of Oʻahu and Molokaʻi, E. koolauensis is now limited to 11 populations with a total of ~99 mature individuals on the island of Oʻahu. Hundreds of asymptomatic fungal species live within the E. koolauensis leaf tissue, and recent studies imply the composition of these foliar fungal communities can affect the severity of pathogens such as A. psidii. Using molecular and culture-based methods, I characterized the foliar fungal community and introduced these diverse fungi in to microbiome of E. koolauensis leaves infected by A. psidii. By manipulating the composition of the leaf microbiome, via application of a leaf slurry and single isolate spore-slurries, I demonstrated how increased fungal diversity promotes resistance to A. psidii in E. koolauensis. These results highlight the potential of harnessing native microbes to induce disease resistance within a conservation context.