Mycorrhiza-induced resistance in wheat leaves and protection against pathogenic fungi
Résumé
More than 80% of land plants can form symbiotic relationships with arbuscular mycorrhizal fungi (AMF), including crops. By associating with plant roots, these beneficial fungi increase the volume of soil exploration, which generally results in better mineral and water nutrition of plants. They are known to improve plant tolerance to abiotic stress, and researches in the last decades have shown that AMF can also induce local or systemic plant resistance to pathogens, which is known as mycorrhiza-induced resistance (MIR).Inoculation of bread wheat roots with a CMA, Funneliformis mosseae, provides protection in controlled conditions against powdery mildew and septoria tritici blotch, two fungal diseases that affect the leaves of wheat plants. This protection is partial and related to the induction of MIR in wheat leaves, in various cultivars. In mycorrhizal plants, the expression profile of some defense-related genes in leaves was modulated before any challenge by the pathogen, suggesting a systemic elicitation of some genes rather than a strict priming of plant defense. Among them, genes encoding PR-proteins, proteins involved in flavonoid and polyamine synthesis were up-regulated. In the early stages after inoculation with Blumeria graminis f.sp. tritici, responsible for powdery mildew, the jasmonate and pipecolic pathways were stimulated. Microscopic analyses highlighted an increase in phenolic compounds accumulation in leaves at the penetration site of the fungus. The induction of defenses and the link between growth and defense will be discussed.