Editorial: Proceedings of iMMM 2019 – International Molecular Mycorrhiza Meeting

This Research Topic was launched on the occasion of the 4th International Molecular Mycorrhiza Meeting (IMMM 2019), held in Torino, Italy, on 7–8th February 2019 (Figure 1) and has collected 13 selected contributions from the IMMM 2019 meeting attendants. The articles include original research, methods, reviews, and perspective papers covering most of the main topics presented at the meeting. These embrace molecular, cellular and nutritional aspects of mycorrhizas, the beneficial plant associations with soil fungi, as well as methodological approaches. Mycorrhizal fungi are considered key components of natural and agricultural ecosystems because they colonize the roots of most land plants developing different types of symbiotic interactions that greatly contribute to plant growth and health. A broad interest is focused on mycorrhizal symbioses, in particular arbuscular mycorrhiza (AM), for their potential contribution to agricultural practices that reduce the use of chemical fertilizers and pesticides and support sustainable crop production to feed a growing human population in a scenario of global climate change. It is therefore not surprising that the majority of contributions to both the meeting and the Research Topic concerned the AM symbiosis. In addition to agricultural applications, the great interest for AM symbiosis also derives from its ecological success (being found in over 72% of land plant species), its long evolutionary history (since plants and AM fungi started to live together at least 400 million years ago), and the refined coordination between major developmental and physiological processes of both partners.