In addition to draught, plants growing in arid soils face two major challenges: high salinity and iron (Fe) deficiency. Salinity attenuates growth, affects plant physiology and causes nutrient imbalance which is, in fact, one of the major consequences of saline stress. Fe is a micro-nutrient essential for plant development. It is required for several metalloenzymes involved in photosynthesis and respiration and Fe-deficiency is associated to chlorosis and low crop productivity. The role of microbial siderophores in Fe supply to plants is well documented as well as the effect of plant growth promoting rhizobacteria (PGPR) on the Page 1 of 41 http://pedosphere.issas.ac.cn Pedosphere mitigation of saline stress in crop cultures. However, the dual effect of siderophore-producing PGPR both on salt-stress and on Fe limitation is still poorly explored. This review provides a critical perspective on the combined effect of Fe limitation and soil salinization as challenges to modern agriculture and intends to summarize some indirect evidence that argue in favour of siderophore-producing PGPR as bio-fertilization agents in salinized soils. Recent developments as well as future perspectives on the use of PGPR are discussed as clues to sustainable agriculture practices, in the context of present and future climate change scenarios.

Root−associated microbial communities play important roles in the process of adaptation of plant hosts to environment stressors, and in this perspective, the microbiome of halophytes represents a valuable model for understanding the contribution of microorganisms to plant tolerance to salt. Although considered as the most promising halophyte candidate to crop cultivation, Salicornia ramosissima is one of the least-studied species in terms of microbiome composition and the effect of sediment properties on the diversity of plant-growth promoting bacteria associated with the roots. In this work, we aimed at isolating and characterizing halotolerant bacteria associated with the rhizosphere and root tissues of S. ramosissima, envisaging their application in saline agriculture. Endophytic and rhizosphere bacteria were isolated from wild and crop cultivated plants, growing in different estuarine conditions. Isolates were identified based on 16S rRNA sequences and screened for plant-growth promotion traits. The subsets of isolates from different sampling sites were very different in terms of composition but consistent in terms of the plant-growth promoting traits represented. Bacillus was the most represented genus and expressed the wider range of extracellular enzymatic activities. Halotolerant strains of Salinicola, Pseudomonas, Oceanobacillus, Halomonas, Providencia, Bacillus, Psychrobacter and Brevibacterium also exhibited several plant-growth promotion traits (e.g., 3-indole acetic acid (IAA), 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, siderophores, phosphate solubilization). Considering the taxonomic diversity and the plant-growth promotion potential of the isolates, the collection represents a valuable resource that can be used to optimize the crop cultivation of Salicornia under different environmental conditions and for the attenuation of salt stress in non-halophytes, considering the global threat of arable soil salinization.

Halophytes have long been used for medicinal purposes. However, for many decades, their use was entirely empirical, with virtually no knowledge of the bioactive compounds underlying the different applications. In recent decades, the growing problem of antibiotic resistance triggered the research on alternative antimicrobial approaches, and halophytes, along with other medicinal plants, regained attention as an underexplored pharmacological vein. Furthermore, the high nutritional/nutraceutical/pharmacological value of some halophytic species may represent added value to the emerging activity of saline agriculture and targeted modification of the rhizosphere, with plant-growth-promoting bacteria being attempted to be used as a tool to modulate the plant metabolome and enhance the expression of interesting metabolites. The objective of this review is to highlight the potential of halophytes as a valuable, and still unexplored, source of antimicrobial compounds for clinical applications. For that, we provide a critical perspective on the empirical use of halophytes in traditional medicine and a state-or-the-art overview of the most relevant plant species and metabolites related with antiviral, antifungal and antibacterial activities.

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