Pampas Project Makes Progress
Biocontrol for pampas (Cortaderia spp.) has always appeared to be rather a long shot. “No potential agents were known at the outset of the project and we needed to find agents with a high level of specificity to avoid harming our closely-related native toetoe Austroderia spp.,” said Lynley Hayes, who leads this project.
Pathogens can sometime be so highly host-specific that strains may attack only limited genotypes of a host plant. This is true for four rust fungi of interest to New Zealand, blackberry rust (Phragmidium violaceum), Chilean needle grass rust (Uromyces pencanus), hieracium rust (Puccinia hieracii var. piloselloidarum), and lantana leaf rust (Prospodium tuberculatum). With such tightly host-specific agents, to avoid host-pathogen incompatibility, it is critical to survey genotypes of the weed in the native range that match what is to be biocontrolled here.
So the first task was to determine where in South America our New Zealand pampas comes from so we could search in the right places. We quickly discovered that current Cortaderia taxonomy doesn’t resolve the genetic complexity in the group, with molecular studies quickly showing that C. jubata and C. selloana from Argentina were not the same as plant material in New Zealand of the same name. Molecular studies allowed us to quickly match our C. jubata with material in southern Ecuador, but a match for C. selloana proved much trickier. With a bit of luck, and the help of a number of South American collaborators, we sourced and genotyped more material from Argentina, Uruguay, Brazil and Chile, and eventually found a match in Chile. However, to complicate matters further, we also determined that some New Zealand pampas was neither C. jubata nor C. selloana, but an entity we commonly encountered in South American material that we can’t accurately name because of the state of Cortaderia taxonomy. Initially we thought this material was rare and recommended these populations be eradicated, but the more we looked, the more we found, and so the project scope has widened to seek biocontrol agents for this plant as well.”
Surveys in South America revealed only two potential control agents worthy of further study; a fungus and an insect. A black smut fungus that damages the flowerheads, reducing seeding, was found in Ecuador on C. jubata and in Chile on another Cortaderia species. Sequencing has shown the Ecuadorian smut is a 100% match with the published strain of Ustilago quitensis, and the Chilean smut is a 98% match. So the two smuts are likely to be the same species, but it is unclear whether they are different strains with different host preferences, and testing is required to resolve this.
However, so little is known about this black smut that we are not even sure how to infect plants with it. The floral plumes emerge already infected and, based on what is known about other similar pathogens, it may be that infection occurs when seeds germinate, creating a systemic infection that only becomes apparent at flowering time. Dr Charlie Barnes (Pontificia Universidad Católica del Ecuador) has two students looking into aspects of this further. In the meantime, with the help of Dr Hernan Norambuena, in Chile, we have imported the Chilean smut into containment and are observing plants that we have attempted to inoculate in several ways. Once we have a reliable method for infecting pampas plants host-testing will be able to get underway.
The other potential agent is a delphacid planthopper that attacks the leaves. Our Chilean collaborators suspected they had found two similar planthopper species and sent us specimens for sequencing. We confirmed the identity of the more common of the two as Saccharosydne subandina, which is reported to have too wide a host-range to have potential as a biocontrol agent. We also confirmed that the less commonly found, planthopper is a novel, un-named species, so no information is available about it at all. With Hernan’s help we have recently imported some of the newly discovered planthoppers into containment for further study. “The planthoppers proved to be extremely fragile to ship, requiring three attempts before we had enough live specimens to form a useful starter colony,” reported Hugh Gourlay. However, once settled in, the planthoppers quickly set about producing offspring and causing obvious damage, and there were sufficient numbers to allow host-testing to get underway within weeks. As an acid test, i.e. ‘fail this and it is all over’, planthoppers were initially exposed to two native toetoe, Austroderia richardii and A. splendens. Fortunately, these did not appear to be suitable hosts, so more comprehensive host-testing of other critical species (including the other pampas entities) is now underway.
Another key investigation was to see if the imported planthoppers, like other similar species, were associated with any phytoplasma, which are specialized bacteria that cause plant disease and something to be wary of. Relatively little is known about phytoplasma diseases in New Zealand, except where they have caused serious problems to native species like cabbage tree (Cordyline australis) and flax (Phormium tenax) and economically important exotic species like potatoes and celery. “We have used molecular tools, to explore the phytoplasma status of the planthoppers that did not survive the shipping,” explained molecular technician Caroline Mitchell. Intriguingly they returned a positive result and 99% match for a bunch of phytoplasmas that relate to Candidatus phytoplasma australiense, the organism responsible for disease in the native plants mentioned above, and thought to occur only in New Zealand and Australia. It will be important now to explore the phytoplasma status of Cortaderia and Austroderia in New Zealand, as part of understanding potential risks posed by the planthopper. If a latent phytoplasma is found in Cortaderia and the planthopper proves highly hostspecific, this could be a damaging combination against pampas.
Funding provided for this project by the Sustainable Farming Fund is drawing to a close. “This project has achieved a lot more than it originally set out to do,” concluded Lynley. Further funding from a variety of sources will be sought to allow studies of the black smut and the planthopper to be completed, and to perhaps gain permission to release them if they prove suitable.
This project is funded by the National Pampas Biocontrol Initiative through a grant from the Ministry for Primary Industries’ Sustainable Farming Fund (11/049), supported by a number of co-funders, including the National Biocontrol Collective.