Pampas proves to be a difficult target
Black floral smut found in Chile. Image - Hernan Norambuena
When we first considered the feasibility of biocontrol for pampas (Cortaderia spp.) back in 2000 we concluded that it would likely be a difficult target. No potential agents were known and agents with a high level of specificity would be needed to avoid harming our closely-related native toetoe (Austroderia spp.). After three years of searching for potential biocontrol agents pampas has indeed proven to be a difficult target, but not always for the reasons we expected!
We initially planned to look for agents in Argentina, the only place in South America where both the problem species in New Zealand, Cortaderia jubata and C. selloana, were reported to occur. “That was when we discovered that 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 material in New Zealand of the same name,” explained Gary Houliston. We were able to quickly match our C. jubata with material in southern Ecuador, but a match for C. selloana proved much trickier. With the help of a number of South American collaborators we sourced and genotyped more material from Argentina plus from Uruguay, Brazil and Chile. When we had almost given up hope, a perfect match for New Zealand material turned up in a handful of plants deliberately planted next to a soccer field in Chile. Tracing the source of these plants, and further sampling around the hotspots, enabled more matches to be identified.
Another revelation, thanks to molecular techniques, was that some New Zealand pampas was neither C. jubata nor C. selloana, but an entity we commonly encountered when sequencing South American material – we can’t put an accurate name on it because of the state of Cortaderia taxonomy. Initially we 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 entity as well.
The next challenge was that surveys in South America turned up only two potential control agents worthy of further study, a fungus and an insect. A black smut 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. “Dr Charlie Barnes (Pontificia Universidad Católica del Ecuador) is undertaking further studies of the Ecuadorian smut for us, and with the help of Dr Hernan Norambuena we are planning to import the Chilean smut into containment later this year for further study,” explained Lynley Hayes, who is leading the project.
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 has no potential as a biocontrol agent as its host range is too wide. The less commonly found planthopper is a novel, un-named species so no information about it is available. With Hernan’s help again we plan to explore the host range of this novel planthopper, and investigate whether, like S. subandina, it is associated with a phytoplasma disease. Relatively little is known about phytoplasma diseases in New Zealand except where they have caused serious problems like cabbage tree decline and flax yellows. A lot more research will be needed to explore whether a potential biocontrol agent that can vector phytoplasma diseases would provide a double-whammy advantage or be total unsuitable.
In case a classical biocontrol approach does not work out, Stan Bellgard has been exploring whether the utility of synthetic and organic herbicides can be increased through co-formulation with a plant pathogen (Nigrospora oryzae) recovered from pampas in New Zealand. “Results to date have been a bit mixed, but work is continuing this year on co-formulation trials using 25% Gallant (haloxyfop) and also pine-oil and pine-oil/ fatty acid commercial formulations, and if we can improve the current spore formulation that could provide a breakthrough,” said Stan.
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.