Fig. 1

Structure of the study (a) and the suggested model linking bacterial diversity of the seed microbiota with colonization resistance against beneficial and pathogenic microorganisms (b, c). In our study, we combined three experimental approaches: a bioinformatic in silico approach, an experimental in planta approach, and a confocal microscopy in situ approach (a). The suggested model (b, c) explains the reactions of oilseed rape cultivars to the treatments with beneficial organisms. We compared cultivars whose seeds contain either high (Sherpa and Traviata) or low (Avatar) bacterial diversity. The seeds characterized by lower bacterial diversity and lower amount of beneficial taxa (schematically shown on the left side of the image) can be colonized by allochthonous cells (depicted as blue rods) in higher amounts than seeds with comparatively higher bacterial diversity (shown on the right side). Therefore, the treatment of seeds showing lower bacterial diversity with beneficial bacterial strains may result in increased resistance towards pathogens (depicted as brown fungal colonies). By contrast, under conditions in which seeds with higher bacterial diversity are treated with the same bacterial strains, the resistance of the seedlings to pathogens is less affected. This model is suggested for plant seeds with a tight bacterial network in which the introduction of new bacterial strains is rather challenging