Screening clones of native pepper (Tasmannia lanceolata) for resistance against Phytophthora cinnamomi

Native pepper (Tasmannia lanceolata) is harvested as a boutique pepper product from wild stands and from plantations. The species has been reported as susceptible to Phytophthora cinnamomi, however surveys in plantations suggest that clones differ in susceptibility. The key objective of this study is to identify native pepper clones that are resistant to P. cinnamomi, and the defence mechanisms responsible. Plant material from native stands of native pepper was collected throughout Tasmania from June-October 2020, and 47 clones were successfully propagated as cuttings in mist beds. A disease screening experiment was conducted in “soil-free plant growth system” units, which were either allocated for inoculation or a non-inoculated control. Four replicates of each clone were placed in both a control and inoculated unit. Lupin seedlings were used as a positive control in all units to validate successful inoculation. Fresh P. cinnamomi zoospores were produced and 20μl droplets of the solution were applied to all root tips of all plants in the inoculation units, while the control plants received droplets of sterile water. Successful inoculation and infection were confirmed via the symptoms on lupin plants and re-isolation of the pathogen from native pepper roots. Visual symptoms of root disease and shoot health were assessed over a 2-week period based on photographs which were then quantified with image analysis. Expression of genes related to defence mechanisms were examined via RNA extraction, at 72 hours post inoculation. Preliminary results show that whilst most clones developed symptoms, a small number from both Northern and Southern Tasmania did not and may be resistant to P. cinnamomi. Results are pending and will be used to refine more targeted studies for the development of rapid screening tools for assessment of resistance.