Plants, like humans have developed adaptive immune systems to enable them to respond to disease threats. In parallel to what has recently been shown in human gut health, microbial diversity on both leaves and roots is an important factor in overall plant health. However, the connections between plant disease and plant-associated microbial communities are not well known. Prevalent plant pathology theories of plant disease and immunity based on laboratory data are not always consistent with ecological studies from agricultural fields. Here our aim is to gain new knowledge about the influence of the interplay between plant disease and other plant-associated microbes on plant health and performance in an agriculturally relevant setting. By investigating interactions between potato and late blight disease, caused by Phytophthora infestans and the related beneficial oomycete Pythium oligandrum we will ask the questions: what role do pathogenic or beneficial oomycetes play in shaping plant microbiomes? and how do these interactions impact health and performance in potato? We will also investigate if P. infestans triggers the newly discovered phenomenon, systemic induced susceptibility and what that might mean for plant health and the evolution of the plant microbiome. These data will help unify our understanding of the community ecology of plant, animal and human systems and advance our understanding of the hologenome theory of evolution.