Potential Climate Change Impacts on Myrtle Rust Risk in Aotearoa/New Zealand

ABSTRACT Austropuccinia psidii is a significant invasive pathogen of tropical origin and is particularly well adapted to warmer and humid climates. Future climate warming in Aotearoa/New Zealand is therefore expected to favour increased activity of the pathogen and consequently more damaging effects from this disease. The Myrtle Rust Process Model, based on A. psidii responses to climatic variables, was used to explore several climate change scenarios that considered increases in temperature in conjunction with decreases in relative humidity (RH). Exploration of the variation and effects of changes in RH on the output of the infection risk model was necessary because of the uncertainty about geographic effects on rainfall and RH associated with climate warming. The climate change scenarios explored were increases of 1°C, 2°C, 3°C, 4°C and 5°C, with corresponding decreases in RH per °C. Infection risk increased with each increased temperature scenario, with the largest increases in areas that are currently only marginally suitable for the pathogen with respect to temperature. Latent periods decreased with increasing temperature, resulting in potential for the rust to continue reproducing over winter in many areas, particularly where, under current conditions, cooler winter temperatures slow or halt pathogen development. Future research is needed to integrate these predictions with host plant distributions and plant phenology, which will also respond to climate change, to understand the impact these increased risks could have on the distribution, survival and regeneration of Myrtaceae plant communities.