Rust spores in gelatin capsules
With only a 3 month timeframe to prepare and ship a starter culture of the rust (a condition of the permit), Freda Anderson (CERZOS – CONICET), our Argentinian collaborator, had her work cut out for her. The packaged spores were shipped on 23 December 2021, which felt like an early Christmas present. We knew that Covid-19 would make shipping difficult, but did not expect the package to take 3 weeks to leave Argentina, and then travel via Tennessee in the USA, before spending a couple of days at the FedEx facility in Auckland. The package was finally delivered and unpacked in the Beever Plant Pathogen Containment Facility in Tamaki on 18 January 2022.
“Within an hour of receiving the spores, Chantal Probst and I inoculated Chilean needle grass plants with a 1:1 mixture of spores and talcum powder,” explained Alana Den Breeyen, who leads this project. “In addition, we did a spore viability test, which involves placing spores on water agar plates, incubating them for 24 hours, and then counting the number that are viable,” she added. After 24 hours Alana and Chantal found less than 1% germination – in other words, only 1 out of 100 spores were viable. Despite this, they were still hopeful that some spores would be infective, waiting 2 weeks to check for yellow spots on the leaves. Unfortunately there was no happy ending: the rust fungus had not survived the long journey from Argentina to New Zealand. The loss of the starter culture was a big disappointment for all involved.
On a brighter note, the international compliance certificate and Memorandum of Understanding remain valid until the end of 2022, and the EPA application time waiver for the Chilean needle grass biological control agent (APP203314) was recently extended until 30 April 2024. This means we can try again to import the rust without too much of an administrative burden.
To ensure the next rust culture arrives in New Zealand in the best possible condition, several steps are being put in place. Firstly, the remaining spores held by Freda in Argentina will be germinated in her lab to obtain a fresh culture of the original rust isolate. Once this colony is well established and producing viable spores, Freda can again start preparations for exporting the rust.
Because Chilean needle grass grows very slowly from seed, Freda and her team started growing plants immediately after they heard the news that the imported culture had not survived. All going well, the plants should reach a size that allows for inoculation by September. When establishment of the colony is confirmed, Freda will again need to apply for an export permit from the Argentinian National Service for Food Health and Quality (SENASA), hopefully by the end of October. To reduce the potential loss of spore infectivity, the spores will then be hand-carried from Argentina to New Zealand, now that this is again possible, ensuring a short transit time. Once again, Freda will have some painstaking work to do, and we remain appreciative of her and her team’s expertise and perseverance.
Despite the many setbacks experienced over the past decade with the Chilean needle grass project, we remain confident that the rust will be successfully re-imported into New Zealand. Once we have a viable culture, the additional host range testing that is required can be conducted.
The rationale behind testing an additional three grass species is based on evidence from Australia that U. pencanus isolate UP 27 was able to produce spores on two Austrostipa species. Neither of these grass species is present in New Zealand, but three of our native grasses (Austrostipa stipoides, Achnatherum petriei and Anemanthele lessoniana) are closely related enough to warrant further investigation. Once testing is successfully completed, if the rust proves to pose no risk to these grasses, and with permission from the EPA to release it, the first releases could be possible in the spring of 2023. That will be a cause to celebrate!
