Effects of Plant Growth-Promoting Rhizobacteria on Wheat Growth under Greenhouse and Field Conditions in combination with different nitrogen fertilizer levels

Many Plant Growth-Promoting Rhizobacteria (PGPR) are able to enhance root growth, mineral availability, and nutrient use efficiency of crops. The aim of this project is to screen commercially available PGPR formulations and lab strains to increase wheat growth and yield in combination with an optimized nitrogen (N) fertilizer application scheme. This could lead to a significant reduction of N fertilizer application without affecting the subsequent grain yields. The screened products collection includes (1) Mix1 (a mix of Azospirillum sp., Azorhizobium sp., and Azoarcus sp.), (2) Mix2 (a mix of Mix1 complemented with two strains of phosphorus-solubilizing Bacillus sp.), (3) Bacillus amyloliquefaciens a, (4) B. subtilis, and (5) B. amyloliquefaciens b. These products were screened under greenhouse and field conditions in 2014 by using spring and winter wheat varieties, respectively. Under greenhouse conditions, there was a significant increase in root dry weight and in root per shoot ratio of plants inoculated with Mix1. Under field conditions, the interaction between PGPR inoculation and different N fertilizer doses was assessed. The grain yield was negatively impacted by low N fertilizer applications. Under such conditions, the inoculation of the wheat rhizosphere with B. subtilis increased the grain yield by 15% relative to the water control. However, in the field trial, the variability between plot replicates was high and lead to non-significant results. Based on these results, modified screening strategies for PGPR selection were set up for the next trials.