The soil-borne legacy: how plants cry out for help in response to disease

Abstract

There is an urgent need to raise agricultural production to feed the increasing world population. To achieve this, solutions that reduce dependence on agrochemicals and support sustainable agriculture are essential. Thus, studies on plant performance and health have focused on sustainable replacements for pesticides and fertilizers. Modern plant breeding programs aim to increase resistance against diseases and pests and to increase plant performance under abiotic stress conditions. These efforts not only focus on the visible parts of the plant but also include the plant parts hidden in the soil. The root system of a plant is not only essential for anchoring and for nutrient and water acquisition, but it is also the hotspot for interactions of the plant with the belowground microbiota. A wide range of pathogens, including fungi, viruses, bacteria, and oomycetes are detrimental for plant health and a major threat to agriculture worldwide. On the other hand there are plant beneficial microbes that can increase plant growth or suppress plant diseases. The fact that soil microbes can have such profound effects on the plant, has made them a valuable target to study. In this thesis, we have focused on the root microbiome in relation to plant health, including effects of disease on root microbiome composition and effects of the microbiome on disease severity. The main research question was if plants under pathogen pressure have an active role in recruiting a specific and protective microbiome and what are the mechanisms involved in such recruitment. In this thesis, we have shown a proof of concept of microbiome modulation as a response to foliar infection using Arabidopsis. We have shown a multitude of changes in the rhizosphere microbiome upon foliar infection, as well as the induction of systemic resistance by this microbiome, under the influence of coumarin exudation of the plant. These mechanisms of the SBL could be exploited to protect crops in a durable way. To conclude, we have lifted a tip of the veil of the incredibly complex system that is plant microbiome-interactions under pathogen pressure, but by doing so created more questions left to be answered.