Evaluating the impact of drought stress in Nure and Tremois barleys (Hordeum vulgare) treated with plant growth promoting rhizobacteria (PGPR) at seedling phase

Barley is the fifth cultivated herbaceous crop in the world, and its important is due to its economic and nutritional value. Climate change is posing a new challenge to barley production. While drought stress was traditionally associated with the flowering and caryopsis filling stages in barley plants, a new form of drought is now emerging in seedling stage. To mitigate the impact of environmental stresses, plant growth promoting rhizobacteria (PGPR) have been proposed to promote nutrient absorption and plant growth with the production of a range of beneficial substances, such as phytohormones, organic acids, and enzymes. The aim of this study was to evaluate the genotype response and the impact of PGPR treatment on two cultivars of barley, Nure (Italian feeding barley, winter habitus) and Tremois (French malting barley, spring habitus) in seedling phase under drought stress. At sowing, the soil was treated with PGPR and after two weeks of control condition two different water regimes were applied on seedlings (control at 25% and stressed at 12% of soil moisture). The results showed that both genotypes exhibited analogous stress response, however the PGPR treatment showed different effects on the two cultivars. Specifically, PGPR treatment increased root dry weight in stress conditions in Nure seedlings (by 36.6%) and increased dry weight in control conditions in Tremois seedlings (by 31.1%). Furthermore, the treatment increased the photosynthesis efficiency (PhiPS2) in Tremois seedlings (by 6.2%) and generally in both cultivars (by 7.6%) under drought stress. These findings suggest that the use of PGPR could be a useful tool for protecting barley seedlings against drought stress in early stages of development. However, further research is needed to fully understand the mechanisms of action to determine the optimal conditions for using this approach in the field.