Towards a more sustainable agriculture: wheat mycorrhization to protect against powdery mildew

One of the means to reduce the use of pesticides, which are harmful for humans and the environment, is the development of alternative methods to control crop diseases. In this context, arbuscular mycorrhizal inoculation possesses a great potential for crop production by a more sustainable agriculture. Our work aims to (i) determine the optimal conditions for wheat mycorrhization (ii) study the impact of arbuscular mycorrhizal inoculation on a foliar disease of wheat, powdery mildew (Blumeria graminis f.sp. tritici, Bgt), (iii) evaluate the stimulation of natural defences of wheat (Triticuma estivum). Therefore, this work consisted firstly of defining the parameters, affecting the establishment of wheat mycorrhization, such as: phosphorus concentration (62, 12.5, 6.2 mg/L), culture time (4, 5, 6, 7 weeks), arbuscular mycorrhizal species used as an inoculum (Rhizophagus irregularis (Ri), Glomus masseae (Gm) and the mixture of (Ri+Gm)) and wheat cultivars (Orvantis and Lord, sensitive and moderately resistant to Bgt, respectively). Secondly, the protective effect of mycorrhizal inoculation against Bgt was estimated by comparing infection rates of wheat seedlings subjected and non-subjected to AMF. Finally, to better understand the biochemical mechanisms involved in the protection, two enzymatic activities described as defense markers [lipoxygenase (LOX) and peroxidase (POX)] were also assessed. Extensive mycorrhization (about 31%) was obtained at P/5 concentration (12.5 mg/L) when wheat plants were 6 weeks old. The highest colonization rate was obtained when wheat was inoculated with Gm compared to SZE and Ri. The higher resistance level of Lord wheat cultivar against Bgt did not affect the mycorrhizal rate compared to the more susceptible cultivar Orvantis. Our work showed a significant protection level in mycorrhizal (M) wheat plants against Bgt, estimated to about 25 and 43% with Ri and SZE respectively compared to non-mycorrhizal (NM) Orvantis plants. The protection levels percent's were about 30 and 64% for Lord plants. The protection was higher for Lord than Orvantis and seems to depend on the resistance degree. These results suggest the induction of a systemic resistance by mycorrhizal inoculation. Our results showed an increase of both activities (LOX and POX) in wheat infected by Bgt for both (M) and (NM) plants by the inoculum SZE (Ri+Gm) at P/5 phosphorus concentration.