Mycorrhizal inoculation protected bread wheat against Septoria tritici blotch.

International audienceSeptoria tritici blotch (STB) is one of the most common diseases encountered in bread wheat crops andcan cause yield losses of up to 50%. Its causal agent, the hemibiotrophic fungus Zymoseptoria tritici(Z. tritici), is developing increasing resistance to conventional fungicide treatments. As a consequence,STB is difficult to control despite ever more treatments with detrimental impact on environment andhuman health. To reduce their use, new control strategies compatible with more sustainableagriculture have to be developed.Mycorrhizal symbiosis occurring between plants and arbuscular mycorrhizal fungi (AMF) is known toimprove plant mineral and water nutrition as well as plant resistance against biotic stresses throughMycorrhiza Induced Resistance (MIR). In this context, the objective of the present work, carried outwithin the framework of the Bioscreen project (Smartbiocontrol, Interreg V), was to study the eventualcontrol of STB through mycorrhizal inoculation with the AMF species Funneliformis mosseae (F.mosseae), and to get insights in the defense mechanisms involved. For this purpose, 6-week-oldwheats (cv. Alixan) susceptible to STB were inoculated with F. mosseae before infection with Z. triticiin controlled conditions. At 18 days postinfection (18 dpi), the mycorrhizal root colonization rate wasestimated at 40% and allowed an 80% protection against STB of mycorrhizal wheats compared tonon-mycorrhizal ones. Leaf and root samples were collected during the biotrophic phase of Z. tritici (2dpi) to monitor the expression of both defense genes induced by the MIR in leaves and genes involvedin nutrient transports relative to mycorrhizal symbiosis in roots. Results show that F. mosseaeinoculated at root level is able to induce genes encoding PR proteins and proteins involved in bothantioxidant systems and the salicylic acid pathway in leaves.The observed protection was essentially based on a systemic elicitation of defense genes since we didnot observe any priming effect during mycorrhizal wheat infection with Z. tritici. Genes involved innutrient exchanges with AMF were induced in mycorrhizal wheat roots with no alteration by STB,except for SWEET transporters which were induced only in infected wheats. On the whole, theseresults lead us to propose F. mosseae as an interesting candidate biocontrol agent for field trials