BIOTECHNOLOGICAL SOLUTIONS FOR SUSTAINABLE APPROACHES IN AGRICULTURE: THE CASE OF PLANT GROWTH PROMOTING BACTERIA

This PhD thesis was developed within the National Research Center for Technology in Agriculture (AGRITECH) project, which was funded under the National Recovery and Resilience Plan (PNRR). The AGRITECH project generally promotes the development of innovative technologies in the agricultural sector to improve production quantity and quality, ensuring sustainable adaptation to climate change through risk prevention, resistance and resilience, such as in the case of drought, health emergencies and soil depletion. Sustainable intensification of crop production is challenging, particularly in Mediterranean regions such as Apulia, where drought and related biophysical and biochemical factors create unstable environmental conditions. Therefore, new management models must be developed to enhance agricultural productivity and promote resilience to climate change. Using Plant Growth-Promoting Bacteria (PGPB) as biofertilizers is a promising eco-friendly alternative to current agricultural practices. PGPBs promote plant growth while reducing environmental pollution and the need for external inputs, such as nitrogen and phosphate fertilizers, by improving the efficiency with which these nutrients are used. In this context, the use of native PGPB, which is isolated from the soil and able to adapt to environmental stress, is a particularly promising tool for promoting plant growth. The aim of this PhD thesis was to select and evaluate native PGPB isolated from the rhizosphere of durum wheat for their use as biofertilizers, with the intention of improving nutrient use efficiency, yield and quality in sustainable crop systems under a Mediterranean environment. To achieve this aim, the following objectives were pursued: i) the technological characterization of autochthonous PGPB isolated from durum wheat rhizosphere, in order to select in vitro the most promising strains; ii) the evaluation of the effect of process variables and substrate on biomass production; iii) the investigation the effects of PGPB, used either individually or in combination with other agronomic inputs, on crop yield and modulated soil microbial characteristics. Therefore, six wild strains (spore-forming bacteria or pseudomonads) were used as test microorganisms. The isolates were initially characterized in terms of their resistance to fungicides, their ability to adhere to seeds, and their capacity for environmental adaptability. Then, the most promising bacteria were tested as an inoculant in preliminary soil trials on various crops, including wheat, chickpeas and peppers. As a secondary step, the conditions for biomass production, both with conventional and unconventional growth media, were tested. The results obtained generally showed the technological robustness of the strains. Moreover, agronomic studies confirmed that inoculation with the strains modulated soil microbial characteristics, positively influencing yield response and improving agronomic parameters (e.g., shoot biomass, nitrogen uptake and nitrogen use efficiency (NUE) and water use efficiency), particularly under low fertility conditions. The experiments on biomass production confirmed the importance of some parameters on the viability of the strains but also show the possibility of using unconventional growth media, produced from artichoke wastes, in the framework of a circular economy system.