[en] Plant Growth-Promoting Rhizobacteria (PGPR) are one of the main biostimulant classes due to their capacity of stimulating root growth and enhancing soil mineral availability, hence increasing nutrient use efficiency in crops. The aim of this study is to screen commercially PGPR-containing products to enhance 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 biostimulants were screened under greenhouse and field conditions in 2014 by using spring and winter wheat varieties respectively. 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 N fertilizer application was assessed. The grain yield was negatively impacted by low N fertilizer applications. Under such conditions, the inoculation of the wheat rhizosphere with Bacillus 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 those results, modified screening strategies for PGPR selection were set up for the 2015 trials to reduce field variability and possibly achieve higher yield increases.
