Fungi and other filamentous microbes called oomycetes cause many devastating plant diseases and are together responsible for more than 10 percent of all crop loss. A groundbreaking new study now shows that even healthy plants host potentially harmful fungi and oomycetes in plant roots. That they do not succumb to illness is due to the simultaneous presence of a wide range of co-residing bacteria, which regulate the balance among these microorganisms in plant roots and thus ensure plant survival in nature. These are the conclusions of a study published in the journal Cell that was led by Stephane Hacquard and Paul Schulze-Lefert at the Max Planck Institute for Plant Breeding Research in Cologne, Germany.