Droughting results in lower than genomically predicted susceptibility to myrtle rust in Melaleuca quinquenervia

Karina Guo , Geoff Pegg, Karanjeet Sandhu, Glenda Wardle, Jason Grant Bragg

• Ecological restoration often involves founding or supplementing plant populations. To support long-term resilience of these populations, we aim to promote their capacity to respond to known and unknown challenges of climate and disease. In this study, we set out to inform restoration by characterising the interacting effects of climate and disease stress on a foundation tree species.

• Melaleuca quinquenervia is a widespread ecological foundation species that form the canopy of extensive wetland ecosystems. It exhibits varying susceptibility to the disease myrtle rust (Austropuccinia psidii). In this study we conduct a glasshouse experiment to observe resistance to rust following drought treatments. We compare this post-drought rust resistance to Genomically Estimated Breeding Value for rust resistance for the same individuals (N = 671). Six drought treatments were applied, with all combinations of three drought severities (low, moderate, and high) and two drought lengths (33 and 62 days). 

• Our drought treatments resulted in plants exhibiting higher than expected resistance (reduced susceptibility) to myrtle rust. This drought induced resistance, however, rapidly degraded when water replete conditions were restored. Seedlings from resistant maternal lines stayed relatively resistant across drought treatments.

• This study illustrates the benefits of understanding the resistance of seed lots used for restoration. Under forecasts of increased drought severity and lengths, resistant seed lots are expected to maintain resistance under varying drought conditions. We therefore recommend the incorporation of resistant seed lots in the design of restoration projects to improve the resilience of populations in the long-term.