Age‐related susceptibility ofEucalyptusspecies toPhytophthora boodjera

Abstract

Phytophthora boodjerais a newly described pathogen causing damping off and mortality ofEucalyptusseedlings in Western Australian nurseries. This study evaluated the age‐related susceptibility of several taxa of malleeEucalyptustoP.boodjerain sterilized washed river sand‐infestation pot trials.Phytophthora cinnamomiandP.arenariawere included for comparison. Seedlings ofEucalyptustaxa were inoculated at 0, 2, 4, 12 and 88 weeks with individualPhytophthoraisolates. Pre‐emergent mortality in the presence ofPhytophthorawas almost 100%. Post‐emergent mortality was 50–100%, depending on isolate, compared to 0% for the control. Mortality was also high for inoculated 1 month‐old seedlings (46–68%) and root length of surviving seedlings was severely reduced. Death from root infection was not observed for seedlings inoculated at 12 and 88 weeks, but they developed root necrosis and reduced root dry weight compared to non‐inoculated controls.Phytophthora boodjerais a pre‐ and post‐emergent pathogen of mallee eucalypts. These eucalypts are susceptible toP. boodjeraat all life stages tested, but the mortality rates declined with plant age. Similar results were obtained forP. cinnamomiandP. arenaria. The events leading to its recent appearance in the nurseries remain unknown and further investigations are underway to determine if this is an introduced or endemic pathogen. The approach used here to understand the impact of aPhytophthoraspecies on multiple hosts at different seedling ages is novel and sets a benchmark for future work.