Plant growth-promoting rhizobacteria (PGPR) in Cannabis sativa ‘Finola’ cultivation: An alternative fertilization strategy to improve plant growth and quality characteristics

The massive employment of chemical fertilizers entails substantial costs for agriculture and leads to significant environmental pollution, soils depletion and crop productivity declines. The aim of this preliminary study was to evaluate the suitability of plant growth-promoting rhizobacteria (PGPR) as an alternative fertilization approach in Cannabis sativa L. ‘Finola’, one of the low-psychoactive substances industrial hemp varieties cultivated in the Abruzzo territory. The PGPR inoculum was first studied in a model system by monitoring the colonization and survival of bacteria in roots of hemp seedling grown in vitro. Following a complete randomized block design with three replicates, female plants were also cultivated in greenhouse and subjected to different cultivation conditions: (i) two different PGPR inoculum concentrations, (ii) nitrogen fertilization, and (iii) unfertilized control. At the flowering stage, plant growth parameters, main cannabinoid content, antioxidant, and total phenolic content, were assessed. In the model system experiment, scanning electron microscope (SEM) imaging revealed an excellent ability of bacteria to adhere to the surface of roots, and to colonize root vascular tissues of hemp seedlings. Under greenhouse conditions PGPR favored plant growth and development as well as plant secondary metabolites accumulation and, consequently, antioxidant capacity. In particular, the lowest PGPR concentration allowed obtaining results comparable with those induced by the recommended nitrogen fertilization. These results underline the potentiality of PGPR application in hemp plants in terms of both higher biomass accumulation and chemical composition, also meeting environmental goals such as an increase in soil biodiversity and a reduction in chemical inputs. This study represents the first step toward the potential application of PGPR in hemp cultivation and could be the base for future extensive evaluations