Biological control of great brome (Bromus diandrus) in durum wheat (Triticum durum): specificity, physiological traits and impact on plant growth and root architecture of the fluorescent pseudomonad strain X33d

The rhizobacterial strain X33d was previously shown to suppress the growth of the weed great brome (Bromus diandrus Roth.). The aim of this work was to identify X33d, characterize its physiological activities, assess its specificity on different non-target crops, and its impact on the growth and the root architecture of great brome and durum wheat (Triticum durum Desf.) grown alone and together. Based on 16S rDNA sequencing, X33d was identified as Pseudomonas trivialis. The specificity assay, performed on a mixture of soil/sand/peat, highlighted the suppressive activity of P. trivialis X33d against great brome and the promoting effect on most of the considered crops, especially durum wheat. Although the growth of durum wheat on quartz sand was unaffected, P. trivialis X33d suppressed the growth and affected the root architecture of great brome, especially when co-seeded with durum wheat. Great brome plants inoculated with X33d and co-seeded with durum wheat showed low root biomass, short root systems and low surface area, volume and number of tips. Moreover, P. trivialis X33d synthesized indole-acetic acid (IAA) that could be involved both in great brome growth suppression and durum wheat growth promotion. Our results indicate that P. trivialis X33d could be exploited as a potential biocontrol agent against great brome without affecting the durum wheat growth. These results are discussed in relation to the competitive capability of great brome towards durum wheat.