Evaluating the Plant-Growth-Promoting abilities of novel halotolerant bacteria under salt stress conditions and their biotechnological application.

Soil salinization is related to a progressive accumulation of salt reducing plant growth and productivity, and it is also one of the main causes of the loss of arable land, threatening global food security. Plant-Growth-Promoting Rhizobacteria (PGPR) can be also used to improve crop resilience in saline soils and counteract their deleterious effects. The aim of our study was to physiologically, genetically, and biochemically characterize four halophilic/halotolerant bacterial strains isolated from the rhizospheres of either maize or quinoa, and to evaluate their potential as PGPR under saline conditions. The isolated strains belong to the genera Bacillus and Halomonas, two taxa known for their ability to produce plant-growth-promoting factors such as indole-3-acetic acid (IAA), siderophores, phosphatases, or ACC deaminase. In our case, it was observed that the production of these compounds and enzymes varies in relation to the NaCl concentration and bacterial strain used. Specifically, the production of IAA was promoted by the presence of NaCl by Halomonas sp., whilst the opposite was true for Bacillus sp. Moreover, our research also aimed to conduct an in vivo assay of their PGP features, inoculating tomato seedlings and growing them under saline stress. At the end of the experiment, morphometric and biomass data were collected, showing an increase in root length and fresh weight in the case of PGPR inoculum with respect to the control. To date, this study is still ongoing; we are investigating oxidative stress and tomato epigenetic modifications caused by both salt and bacterial consortium. Furthermore, the data obtained in our work have allowed us to prove that the bacteria were, effectively, PGPR; however, further studies are needed to evaluate their potential usefulness in biotechnological applications aimed to counteract saline stress on agricultural crops.