Modelling climatic suitability for myrtle rust with a widespread host species

Globalisation has resulted in the spread of infectious plant diseases to new regions and host species and the novel disease caused by myrtle rust poses a global threat to naive hosts in the Myrtaceae family of plants. This study uses a focal species, Tristaniopsis exiliflora, to explore the climatic and microclimatic preference of the myrtle rust disease (Austropuccinia psidii). Populations of T. exiliflora were sampled across the species distribution in Far North Queensland, Australia, modelling A. psidii severity as a function of macro- and micro-environmental variables. Disease severity was found to increase with annual precipitation and foliage projective cover, and decrease with maximum temperature and valley confinement. A subsampled population found that individuals with lower canopy heights experienced more severe disease. Our results suggest that, in tropical environments with seasonal rainfall, A. psidii virulence is reduced when mean annual rainfall is less than 1500 mm and virulence is substantially reduced when maximum temperatures exceed 32 °C. The climatic drivers identified in this study align with optimal in vitro conditions for A. psidii germination and development. This suggests that climatic conditions are regulating myrtle rust in natural ecosystems at a broader scale, and that increased conservation efforts should focus on species with narrow climatic distributions and highly susceptible regions such as the Wet Tropics World Heritage Area.