Interactions between symbiotic and pathogenic fungi in the invasive weed, Impatiens glandulifera (Himalayan balsam)

Impatiens glandulifera or Himalayan balsam is an invasive plant species which is commonly found in riparian habitats and may threaten the biodiversity in the UK by suppressing other native plants, blocking drainage systems and potentially, leading to soil erosion during winter. Between 2006 and 2010, a rust fungus, Puccinia komarovii var. glanduliferae was first identified infecting balsam in its native range (Western Himalayas). Subsequently, the rust was released for the first time in Europe in August 2014 as a classical biological control (CBC) agent on balsam. This study was initiated to observe the effectiveness of the rust on balsam growth and to determine the factors that affect its impact in the field particularly insects presence, arbuscular mycorrhizal fungi (AMF) and endophytic fungi. An investigation on the interactions of fungi and insects on balsam was conducted. It was found that the combination of aphids, mycorrhizas and endophytes affected plant performance, dependent upon the fungal identities. The interactions between balsam and associated microbial communities through plant soil feedback (PSF) experiment was examined too. In contrast to a previous study of balsam, a negative PSF was recorded whereby plants were shorter, lighter and had lower AMF colonization in a soil that had previously supported balsam, compared to control soil. The competition between balsam and two native plant species was examined in the next chapter, to determine the effect of AMF on balsam competitive ability. It was discovered that mycorrhizas reduced balsam biomass when it was grown singly but tended to increase when it was grown in both inter- and intra-specific competition. Finally, the last experimental chapter examined how AMF and endophytic fungi influence the efficacy of the rust fungus, as a CBC agent. It is suggested that both fungi negatively affected plant growth and rust development.