Effects of drought stress and above-belowground microbes on multitrophic interactions in Solanum tuberosum L.

Abstract

Environmental stressors remain a crucial problem in agriculture. Abiotic stress conditions such as drought and biotic stress like insect pests cause extensive losses to agricultural production worldwide. Therefore, to face these challenges novel practices must be developed for improving crop health and crop protection. Microorganisms below and aboveground play key roles in agroecosystem processes and can influence interactions between crops, insect pests and their natural enemies. However, the mechanisms involved in shaping these interactions are often not sufficiently well understood to be used in agricultural practices. The aim of this thesis was to investigate the impacts of microorganisms above- and belowground, and abiotic (drought) stress, on the outcomes of multi-trophic interactions using potato Solanum tuberosum (L), the potato aphid Macrosiphum euphorbiae and its parasitoid Aphidius ervi as a study system. Deciphering and characterising the mechanisms involved in these complex interactions can highlight opportunities for developing and improving pest control under future climate scenarios. The start of this thesis provides a general overview on interactions of microbes above and belowground with plants and insect pests, their natural enemies, and a biotic stressor (drought). Following this, in Chapter 2 interspecific competition between Macrosiphum euphorbiae and the peach-potato aphid Myzus persicae colonising the same plant is investigated under drought stress compared with unstressed conditions. In Chapter 3, the effect of root-colonising arbuscular mycorrhizal fungi (AMF) on plant responses to a combination of stressors (drought and aphid infestation) is investigated. In Chapter 4, the influence of aphid facultative bacterial endosymbionts on parasitoid attraction to aphids is assessed through analysis of volatile organic compounds released from aphid honeydew. In Chapter 5, parasitoid responses to aphid infested plants grown in soils with different cultivation histories and soil microbial communities are examined. Finally, Chapter 6 discusses these findings on above-belowground interactions in relation to developing new approaches for aphid pest control under the changing climate and presents directions for further research.