S21 - Session O2 - Keynote: How we can optimize the interaction of micro-organisms and plants in organic systems for better nutrition

Authors: Marc-André Selosse *

The plant has long been viewed as an autonomous organism, but we now tend to see it as a host for microbial communities (= microbiota), with which it forms a holobiont. Holobiontic interactions range from roots (e.g., with fungal associates of the mycorrhizal symbiosis) to shoots (with protective endo- and epi-phytic microbes) and even seeds (which are the place for vertical transmission of some microbes) and development (e.g. with natural pruning). Plant protection, development and nutrition are shaped by these interactions which were not only poorly used, but also sometimes harmed by conventional practices. Microbes open new perspective and the gate to use them to assist organic systems, especially for better nutrition. Enthusiasm for microbial tools is really promising but yet, should not go without methods. A guideline of good practices includes: (i) local inoculum and strict exclusion of exotic inoculum without proper assessment of invasive potential, (ii) published report of clear results for the solution on sale, and (iii) existence of precise technical advice for application. In middle term, selection of new plant varieties more responsive to microbes may also be required. Microbial practice should be stringent and convincing, to meet the hopes they rise without deception. As for nitrogen fixation by bacteria associated to legumes, one may hope that indirect technics (handling plant and soil to indirectly favore plant-helping microbes) may simply help to ‘wake up’ the microbial sleeping beauties that are surrounding plants and cultures.