Impact of individual and combined abiotic and biotic stress on plant performance and bacterial root microbiota of tomato Recently crops encounter an increased number of individual and combined abiotic and biotic stress which severely affect their growth and yield. Plants are associated with a large number of microorganisms including beneficial as well as pathogenic microorganisms. The interaction of plants with beneficial microorganisms can exert a substantial impact on plant growth and health and their potential can be utilized in sustainable plant production systems. Currently climate change will increase the impact of stress on crops which will more likely be exposed to combined abiotic and biotic stress. At present knowledge on how abiotic and biotic stress and the combination of both stresses affect the plant performance and the microbiome is limited. Soil borne pathogens are responsible for relevant economic losses and are difficult to control. The root bacterial endophytes have shown potential in alleviating stress on plants and improving crop yield and quality. This raises the question how individual abiotic stress like salinity (ionic) and drought (osmotic) and the combination with biotic stress (Verticillium dahliae or Fusarium oxysporum) affects the root microbiota and thus the performance of the plant. Therefore the goal of this thesis was to improve the understanding of the impact of individual and combined biotic and abiotic stress especially the endophytic root microbiota and thus plant performance. The work is focused on the economically important horticultural crop tomato. [...]