International Effort Underway against Tutsan
Tutsan (Hypericum androsaemum) is an invasive weed that originates from Europe and has become a significant pest in the North Island.
The Tutsan Action Group secured funding to conduct a feasibility study into the potential for tutsan biocontrol and this was carried out by Ronny Groenteman in 2009. Given the lack of other effective control measures and that there are no closely related plants used for economic purposes in New Zealand, Ronny recommended that the programme should proceed. She noted that there are two endemic Hypericum species (one of which is threatened with extinction) so cautioned that any agents would have to be highly host specific. Ronny recommended that the following steps be undertaken:
- Map the current distribution of the plant in New Zealand to get a better understanding of the extent of the tutsan problem here.
- Use molecular techniques to assess the origin of New Zealand material.
- Survey plants in New Zealand to see what insects and pathogens already occur on tutsan that might negatively affect biocontrol attempts.
- Survey plants in its native range for potential agents.
Over the past year there has been significant progress in addressing these points.
Elizabeth (Lizzie) Rendell, a British intern, recently spent 6 months with Landcare Research, teaming up with Hugh Gourlay to undertake surveys of New Zealand tutsan. They surveyed 37 sites around New Zealand to determine the extent and density of tutsan distribution. The most significant infestations were found in Taumarunui and the Eastern Bay of Plenty, with most sites in the South Island only consisting of a few plants. The amount of damage to plants from insects was low (approximately 4%) and the majority of this was caused by generalists like the bronze beetle (Eucolaspis brunnea) and leafroller caterpillars. “This is an important finding,” said Hugh. “It means that if insects are eventually brought to New Zealand for biocontrol of tutsan, they are unlikely to displace native invertebrates or face too much competition for resources.”
Lizzie commonly found the tutsan rust (Melampsora hypericorum) during her surveys. This rust is also commonly found on tutsan in Australia, and initially looked promising as an agent, but more recent studies have found it has some drawbacks. A number of successive rust outbreaks are required to kill vigorous plants, and if the environmental conditions that trigger rust outbreak do not strike regularly, some plants can recover between attacks. In addition, tutsan populations are thought to vary in their susceptibility to the rust, and strains of the rust can vary in their pathogenicity (ability to cause disease)!
Currently it appears that tutsan is not behaving in an invasive manner in the South Island while tutsan in the North Island is becoming widespread in some regions. We are not yet sure why there is a difference between the two islands, and whether the rust is implicated at all. At least part of the answer may lie in the recent finding that the two populations have different genetics. DNA from plant material collected from 13 sites from throughout New Zealand has been analysed and we appear to have two distinct groups. Plants from the South Island are genetically similar and, from a limited amount of published data available, appear to match some material found in the UK. North Island populations are also similar to each other (but different to South Island material), and originate from an as yet unknown European site. “The benefit of pinpointing where the plant originates from is that we can target that specific region to look for potential agents, including perhaps other strains of the rust that might be better adapted to attack New Zealand tutsan,” said Hugh. It is fortunate the tutsan in New Zealand is not more genetically variable, as this could potentially have made the project more challenging.
Meanwhile in the Northern Hemisphere, CABI Europe – Switzerland has been contracted to survey tutsan in its native range to look for natural enemies and collect material for DNA sampling. Such surveys have not been undertaken before and we are hoping they will uncover some potentially useful biocontrol agents. This year, MSc student Elena Olsen has joined CABI to undertake the surveys, which will continue until 2013. Elena has initially focused on the UK, Ireland, France and Spain, and has already found a foliage-feeding beetle and a stem-boring moth that appear to be worth further study. The plant material collected by Elena will undergo DNA analysis to see if we can find a match for our North Island plant populations. This molecular work will be carried out in September by Lizzie, who is now back in the UK, using skills she learnt during her time with us.
In addition to Lizzie and Elena this project is benefitting from other international co-operation. Chantal Morin, a plant pathologist with experience in working with Melampsora species, is currently collaborating with CABI and helping Elena with rust identification and virulence testing. Also, an Australian student, Tracey Nel, has recently submitted a Masters thesis on her research that attempted to better understand why some plants are susceptible to the rust in Australia while others are not. She will be meeting up with Chantal and Elena shortly to share her findings. “Hopefully before too long we will have a better idea about whether tutsan rust offers any further biocontrol potential, and what our other options might be,” explained Hugh.
This project is funded by an MPI Sustainable Farming Fund grant to the Tutsan Action Group, with contributions provided by other co-funders.