L'impatto della simbiosi micorrizica arbuscolare (AM) sulla tolleranza allo stress idrico del grano ​

Durum wheat (DW, Triticum durum (Desf.)) is one of the world's most consumed cereal grains, and its most important growing area is situated in the Mediterranean Basin, which produces about 60% of world production. In areas the amount and occurrence of rains fluctuate drastically between years and locations, resulting in significant yield variations. Therefore, improving yield under water-limited conditions is one of the most important challenges for wheat production, particularly in the current scenario of climate change. The thesis is part of the PRIMA’s project EXPLOWHEAT, which has aims to investigate which variety of DW tolerate drought, to face climate change. We also exploited the ability of DW to established arbuscular mycorrhizal (AM) symbiosis, a mutualistic association between plant and soil fungi, which confers benefits directly to the host plant’s growth and development, and improves plant tolerance to drought. To assess DW responses to drought, we considered two DW cultivars (Etrusco and Svevo) in association (MYC) or not (CTRL) with an AM fungus (Funelliformis mosseae). A set of plants for each condition was maintained in well-watered (W) condition, while in a set was imposed a water stress regime (S). Morphological data highlighted that, in both cultivars, drought stress did not impact the root length in CTRL and MYC conditions, while the shoot length and root and shoot biomass were negatively affected by the presence of water stress and by AM symbiosis. Moreover, drought stress drastically decreased the relative water content (RWC %) in both cultivars and negatively affected the fungal colonization in terms of both intensity of mycorrhization and arbuscules abundance. Gene expression analyses focused on some drought-responsive genes suggested that MYC plants differentially perceived water deficit compared to CTRL plants, mainly in the Svevo variety. By contrast, the expression profiles of sulphate transport genes were highly expressed in Etrusco wheat roots compared to the Svevo variety. Furthermore, up-regulation of genes belonging to the S assimilation pathway (OASTL and SAT) has been observed in MYC plants (both Etrusco and Svevo) compared to CTRL plants. The nutritional status has been also monitored by analyzing anions and cations concentrations in leaves. Our findings revealed that water stress increased Na+ content and decreased Cl- level in Svevo leaves of MYC plants. Interestingly, SO42- content was higher in both Etrusco and Svevo leaves of well-watered MYC plants compared to the other conditions. The S index revealed that Etrusco might face a more severe S starvation with respect to Svevo under drought and that AM colonization positively impacts S nutritional status in both varieties. Our findings indicated that i) drought stress negatively affects DW growth (i.e. biomass) and AM colonization level; ii) the outcome of the AM symbiosis seems to be genotype-dependent; iii) different regulating mechanisms of S homeostasis under drought between genotypes occurred; iv) AM symbiosis improves S content in DW leaves.