Seed Inoculation with Hartmannibacter diazotrophicus and Wide Row Spacing: Starch and Protein Properties of Malting Barley Grains

Abstract The organic cultivation of spring barley is becoming increasingly popular, but the prohibition of herbicides and the reduction in mineral fertilizer use pose challenges in achieving optimal yield and quality. While the use of Plant Growth Promoting Rhizobacteria (PGPR) has been suggested to enhance soil fertility and crop productivity, its impact on the starch and protein quality of malting barley remains unclear. This study seeks to assess whether the seed inoculation with PGPR ( Hartmannibacter diazotrophicus ) and wide row spacing influence grain storage protein subunits and starch concentrations in harvested spring barley grains, and whether the effect of strain E19 T varies between different locations. The study was conducted over two consecutive years at three locations in Germany. Protein subunits were analyzed using SDS-PAGE (sodium dodecyl sulfate–polyacrylamide gel electrophoresis), while amylose and total starch content were determined photometrically. Bacterial inoculation with strain E19 T significantly increased total protein and amylose concentrations, as well as specific protein fractions such as hordeins and albumin/globulin-protein Z of the harvested grains, particularly under organic farming conditions. The effects of strain E19 T varied by location, reflecting the influence of environmental factors on its efficacy. Wider row spacing slightly increased hordein and glutelin levels, likely due to improved light absorption of the plant canopy and improved nutrient availability. Microbial seed inoculation with strain E19 T and wider row spacing can contribute to improve the quality traits of spring barley by enhancing nutrient availability and protein synthesis. However, the effectiveness of these practices varied by location, highlighting the need for a site-specific approach to optimize barley production. Integrating microbial inoculants with strategic agronomic practices supports sustainable agriculture while improving crop performance.