Effect of Biostimulants Containing Rhizobacteria on the Growth of Wheat, Barley, and Oilseed Rape Under Various Soil Moisture Conditions

Preparations containing appropriate microorganisms stimulate plant growth and are increasingly used to alleviate plant stress, including water deficit stress. Despite the growing interest in PGPR, little is known about the post-emergence efficacy of formulations based on native strains under water stress. In this study, we tested the post-emergence efficacy of preparations based on Bacillus velezensis_KT27 and Bacillus subtilis + Pseudomonas simiae + Bacillus velezensis_S103 at doses of half a liter and one liter × 200 L × ha−1 in culture fluid or oil dispersion each at a final microbial cell concentration of 5 × 108 (CFU/mL) for the tested strains. Our hypothesis was that the different biostimulants may positively affect plants’ tolerance to water stress. To this end, analyses of plant height, fresh weight, dry weight, chlorophyll, flavonol and anthocyanin content, and chlorophyll fluorescence were conducted under greenhouse conditions for winter wheat, winter barley, and winter oilseed rape. The preparations promoted the growth and water-stress tolerance of the selected plants, with effectiveness depending on strain, plant, dose, and formulation. B. velezensis_KT27 (0.5 L in oil dispersion) increased the dry weight of winter wheat by 17% (optimal) and 14% (water deficit stress) and of winter barley by 17% and 28%. Bacillus spp. + Pseudomonas spp. (0.5 L in oil dispersion) increased winter oilseed rape dry weight by 13% in both conditions. These findings highlight the potential of Bacillus spp. and Pseudomonas spp. for post-emergence biostimulation under variable soil levels of moisture.