Kauriland Summit 2021
Theme 6: Host, Pathogen & Environment
Q&A / Discussion
Do we understand the infection process of Phytophthora agathidicida on roots at the same level of detail as our understanding of myrtle rust infection on leaves?
While myrtle rust has only been in New Zealand for a short period of time, it isn’t new to science and has been known of since the 1800s. However, for kauri dieback it is a ‘new to science’ species, so these are very different timeframes for gathering knowledge.
At the moment we have more information about how myrtle rust infects its host and are just bringing over knowledge from other countries and checking to see if it is the same for New Zealand. A fair amount of work has been done looking at the infection process for kauri dieback, and we have some understanding via some microscopy work led by Stan Bellgard looking at infection from the root tips and the progression of the pathogen up through the fine roots. However, when the infection process is happening below ground it is hard to track those natural processes in real-time.
What do we know about northern rātā (juvenile or mature) as a host for myrtle rust, in the ngahere?
There is uncertainty about the level of infection recorded on that host at the moment. There is a need for national monitoring to provide a centralised (national) monitoring information resource. There is information on what species are susceptible and how it is happening across the species, which we don’t entirely know.
We would fully support any lobbying of the government for funding of a national monitoring system that could help provide information that would help answer this question. Monitoring is currently fragmented and information is not accessible at a national level.
Some of the Biological Management Areas (BMAs) that we will be working within for our NRT research are in areas where surveillance and monitoring of northern rātā and will hopefully be picked up through some of the mana whenua rohe work in Te Whakahononga.
Is Phytophthora agathidicida pathogenicity testing on non-kauri hosts continuing following early indications that some other components of the kauri ngahere may also be negatively impacted?
NRT research is focussing on the influence of other Phytophthora species and how they might contribute to disease.
There is a collaborative project between Scion and Plant and Food Research (funded by MPI), focused on some native species that are potential hosts for kauri dieback. Lauren Waller (Lincoln University) is looking at a broader range of species, including invasive weeds. No obvious hosts are presenting themselves in the preliminary stages.
Why can’t citizen science monitor for myrtle rust?
Citizens, as in the general public, can and do monitor for myrtle rust. The major issues at present are: we don’t have a centralised process or system to collate the monitoring that is being done by citizens or other groups/organisations; most of the current citizen science is ad hoc, we need monitoring that’s more regular and involves repeat monitoring of the same plants/ecosystems over time, and citizen science only covers a small portion of our forests. So if we relied solely on citizens we’d miss a huge portion of our native estate that most citizens do not have regular access to.
Does spore abundance play a role in kauri dieback infection rates? I.e. is there a correlation between abundance or oospores and zoospores and infection rates in kaurilands?
At a fundamental level, yes the higher the spore abundance, the higher the level of infection. However, these are not independent of each other and one should be very careful when interpreting pathogen abundance as a measure of disease risk. While inoculum build-up and accumulation within the soil are important factors in Phytophthora epidemiology, inoculum load and spore production are highly responsive to changes in the environment and is reliant on the presence of a susceptible host. Spore abundance is therefore a poor predictor of the risk of host infection when taken as a snap-shot in time and space.
We have the genome sequence of Phytophthora agathidicida from which we can determine pathogen diversity, presence of disease resistance genes and susceptibility to the disease. I understand consultation with mana whenua has been ongoing on this one. What progress has been made as this knowledge would be very helpful to have?
Some progress has been made. We have started discussions with Te Roroa, one of the iwi, whose trees were screened in the Healthy Trees Healthy Future (HTHF) programme, and with Ngāti Rehua on Great Barrier Island (from where the reference isolate of Phytophthora agathidicida was obtained), however, there is a lot more discussion to be had.
We have derived a huge amount of pathogen information but we don’t have the equivalent information on the kauri host genome which could provide important insights into genetic diversity and susceptibility to the disease.
We don’t want to see what happened with the kōwhai where an overseas group collect some leaves of the kauri and just go ahead and sequence it.
The Host, Pathogen & Environment theme is not sequencing the genome of any native plants, kauri or myrtles.