Community consequences of introducing a biological control agent

In the UK, and much of Europe and the rest of the world, invasive weeds are destroying natural habitats through exclusion of native species, reduction of biodiversity, and removal of ecosystem services. Some invasive weeds even damage the groundwork of buildings, causing structural problems. The costs to the UK economy alone totals almost £2billion per year highlighting them as key targets for control or removal. Efforts to control these weeds is also problematic and expensive, partly due to lack of control measures and partly because of the vigorous nature of the plant spread and deep-rooted establishment of the plants. One of these problem plants is Impatiens glandulifera (Himalayan Balsam), which is now the most commonly occurring non-native plant species on riparian (riverside) systems in England and Wales. The plant severely reduces native plant and insect biodiversity and is expensive and difficult to control, because herbicides cannot be used near water courses. Balsam plants die off in winter, leaving exposed areas susceptible to erosion, while summer populations choke water courses, increasing the likelihood of flooding.
DEFRA selected Balsam as target weed for biological control, emphasising the importance of this research. In July 2014, CABI received Ministerial approval to release the rust fungus Puccinia komarovii var. glanduliferae, a pathogen of Himalayan Balsam found in Pakistan and India, at trial sites in the UK. This is the first approved release of a non-native fungal pathogen anywhere in Europe. It therefore provides a unique opportunity to determine the impact of the rust release on the plant and the communities it has invaded. It is important not just to examine what factors affect the efficacy of the rust in the field, but also how native plant communities recover as weed populations decline. This proposal is a joint one involving CABI, Royal Holloway, University of London and the University of Reading. Together, we will monitor rust release, determine the factors that affect its establishment in the field and discover how invaded communities recover after balsam removal. We will conduct this research alongside DEFRA, who have pledged money to monitor rust release.
We will carry out a series of experiments to examine the impact of soil-dwelling beneficial fungi (termed arbuscular mycorrhizas) on rust infection. Mycorrhizas provide plants with essential nutrients and some species are known to increase susceptibility to foliar pathogens. We will also examine the foliar tissues of balsam plants, as these also contain fungi (termed endophytes). New research is emerging to suggest that microbes living on plant surfaces and inside plants could have anti-microbial effects on potential invading pathogens. It is critical to determine whether we can manipulate the plant's growth conditions to maximise the efficiency of the rust, either through encouraging microbes that help the rust or removing conditions for detrimental microbes.
This is a unique opportunity to discover how the native plant, insect and soil microbial communities start to recover after weed removal. Biocontrol is usually about reducing the health or performance of target organisms and to date it has generally been assumed that a native, diverse community will readily establish. However, we know that balsam somehow alters the soil to severely reduce growth of other plants. Thus, a key outcome of the study will be to determine how we can use beneficial microbes to allow native plants to recolonise. A particularly exciting part is that the mycorrhizal fungi which we hope to use to aid rust efficacy also have the potential to help native plants to grow, thus we will be able to develop a unique, double-headed strategy to have a genuine impact on the control of this weed.

The aim of our research is to investigate the outcome of the interaction of the non-native fungal rust pathogen with its host Himalayan Balsam in UK invasion sites. Our two ultimate goals are to determine if there are growth conditions we can manipulate to help the efficiency of the rust infection; and to determine if the rust application will help to restore natural community structure and function. This proposal fits within the NERC strategic priority of Living With Environmental Change in the Tree Health and Plant Biosecurity Initiative mode as it focuses on a serious problem of invasive weed biology in the UK, which can have dramatic consequences on ecosystem structure and function. Furthermore and from a human perspective, it addresses national economic issues through loss of ecosystem services and expense to control the weed. A number of groups aside from academics will also benefit from this work.
1. Engaging with industrial stakeholders. The private sector could benefit through the commercialisation of (1) beneficial microbe products discovered from the experiments and (2) through the development of ecosystem health monitoring technology. Point (1) has commercial potential, because we may either find root colonising fungi or bacteria that have a detrimental effect on the balsam. These may weaken the plant to enhance infection or we may find synergist foliar microbes that enhance the efficacy of the rust. Point (2) could also be developed with industry partners through development of a monitoring system e.g. an ELISA or PCR-based method to identify the presence or absence of community health markers.
2. Engaging with governmental organisations and policy makers. Government organisations and policy makers will benefit by having more detailed information on the efficacy and safety of the non-native rust fungus in the UK environment. This will not only benefit the national agenda for controlling invasive weeds, but could potentially also help inform practice and policy for biocontrol of invasive pests and pathogens. CABI already has excellent government connections that will help to disseminate information from the experiments as it becomes available.
3. Public engagement. The public will ultimately benefit through recovery of riparian ecosystems and restoration of native species. If the rust is successful in controlling the weed, then taxpayers will benefit through downgrading of weed control measures provided by councils. The public will also benefit from our outreach programmes, which will present the data that we generate, highlight the impact of weed invasion on ecosystem functioning, and show that UK science is responding to the public need to develop innovative control measures.
4. Training opportunities. The researchers will benefit from the research in terms of developing generic career skills, through the extensive staff development programmes in each of the three institutions. For example, training will be provided in presentations to both the scientific community and the public, preparation of manuscripts and grant applications, student supervision and participation in public engagement events. The PDRAs will be expected to participate in the 'Programme in Skills of Teaching to Inspire Learning' at each institution. Furthermore, each member of staff will receive scientific training at the leading edge of the discipline. The PDRA at RHUL will be trained in advanced mycological isolation methods and manipulation of the plant microbiome. Liaison with other mycologists at CABI will be invaluable here. The PDRA at Reading will be trained in next generation sequencing technology and the analysis of large data sets. The researcher at CABI will be trained in insect identification and the preservation and archiving of specimen data (insect and fungal). All three will receive training in experimental design and analysis.