## 1 Introduction  
The last century has been characterized by climate change, a global reduction in water resources, environmental pollution, and soil depletion. Soil salinization is among the most significant phenomena contributing to the loss of cultivable soils; in fact, every year, more and more land is degraded by salinization, and it is estimated that more than 50% of the cultivated land could deal with high salt concentration by 2050 [1]. In particular, salinization is a process causing a progressive accumulation of salts such as as sulphates, sodium, or chlorides in the soils [2]. It is frequent in arid and semi-arid areas, in which soluble salts precipitate and accumulate on the surface layers of the soil, causing desertification phenomena. Salt accumulation has different origins: through natural processes (primary salinization) or anthropic activity (secondary salinization) [3]. The primary salinization depends on the lithology of the substrate, the chemical and physical properties of the soil, and its hydrological characteristics; on the contrary, the secondary salinization is related to agricultural land use, and specifically inadequate agricultural management practices, such as the use of poor-quality water (e.g., rich in salts) and the excessive usage of inorganic fertilizers [4]. Based on the values of salinity and sodium quantity, estimated by electrical conductivity (EC), sodium adsorption ratio (SAR), or percentage of exchangeable sodium, saline soils can be classified into: (i) saline, (ii) saline-sodic, and (iii) sodic [5]. Generally, soil is classified as saline when the EC of the saturated paste extract is greater than 4 dS-m\({}^{-1}\)[6]. In this regard, a saline soil is characterized by low water content and high ion concentrations (e.g., Na\({}^{+}\) and Cl\({}^{-}\)), causing significant imbalances in plants' biochemistry and physiology, which in turn negatively affect morphology, growth, and seed germination [7]. Specifically, salinity negatively affects plant reproduction (flowering and fruiting pattern), influencing crop yields and biomass by reducing its productivity, especially in glycopyte plants (e.g., rice, maize, and wheat) [8]. Moreover, salt excess decreases the amount of chlorophyll and the efficiency of the photosystems and also electron transport mechanism in salt-sensitive plants [9]. Furthermore, salt stress induces the generation of reactive oxygen species (ROS), affecting enzyme activities, membrane and cell wall functions, root and shoot development, and growth [10]. One potential approach to counteracting plant stresses, and in particular, the negative effects of soil salinization on glycopytes crops, is the application of plant-growth-promoting rhizobacteria (PGPR). In fact, PGPR promote plant development and the sequestration of metal excess, and consequently reduce biotic and abiotic stresses. The rhizosphere is considered the region of soil surrounding plant roots up to a distance of 1-3 mm [11], and where the interaction between the plant and microorganisms is beneficial for both of them [12]. In fact, plants host a complex microbial community (bacteria and fungi) that closely adhere to the roots, and among them, the PGPR can improve the fitness of the plant through their metabolic activity. The PGPR community depends on plant species and soil's chemical and physical conditions [13]. They promote plants' growth directly, synthesizing hormones, facilitating the up-take of nutrients, or indirectly inhibiting plant pathogens [14].