The hidden world of endophytic fungi mediating plant-insect interactions
Stefan Vidal
Georg-August-Universität Göttingen, Department für Nutzpflanzenwissenschaften
Abteilung Agrarentomologie
Fungal endophytes (i.e. fungi that live internally within the tissues of their host plant without causing visible signs of infection) are ubiquitous associates of higher plants, found in virtually every organ from every plant species examined so far. In the past research concentrated on clavicipitaceous endophytic fungi that are vertically transmitted (via seeds) and systemically associated with grasses. These fungi are thought to interact mutualistically with their host plants mainly by the production of secondary compounds, including alkaloids, which benefit plants by increasing their competitive ability and resistance to biotic and abiotic stress factors. However, the vast majority of fungal endophytes form internal localized infections in foliage, roots, stems, and bark, and are horizontally-transmitted via spores. To date the interactions between these omnipresent unspecialized endophytes in their host plants and herbivores, feeding on these plants, remain largely unexplored.
We used a widespread and non-specialized genus of endophytic fungi, Acremonium spp., to test, whether these fungal endophytes interact with their host plants, and thus mediating effects on higher trophic levels. Using different host plant-endophyte-herbivore-systems we found consistent pattern with regard to these interactions: Colonisation of endophytes proved to be antagonistic towards herbivorous insects, but plants did not suffer from endophyte growth. Herbivorous larvae experienced higher mortality when feeding on plants colonised by the fungi, and negative effects translated even into the next generation. On the other hand, plants colonised by an endophyte were more attractive for adults, stimulating oviposition, resulting in a paradoxon of “mother’s don’t know best”. Explanation for this paradoxical behaviour will be discussed.
There is now ample evidence that endophytes induce changes in the metabolism of their host plants mediating herbivore preference and performance pattern. Potential applications for using these endophytes in plant protection strategies will be outlined.
