Non-native PGPB Consortium Altered the Rhizobacterial Community and Slightly Stimulated the Growth of Winter Oilseed Rape (Brassica napus L.) Under Field Conditions

Plant growth-promoting bacteria (PGPB) are among the most promising alternatives to mineral fertilizers. However, little is known about the effects of applied bacteria on the native microbiota, including the rhizobacterial community, which plays a crucial role in bacteria-plant interactions. Therefore, this study is aimed at assessing the effects of PGPB not only on plants but also, importantly, on the native rhizobacterial community of winter oilseed rape. The bacterial consortium, consisting of Pseudomonas sp. KR227 and Azotobacter PBC1 (P2A), slightly promoted plant growth, increasing the root weight by 21.95% and seed yield by 18.94%. This likely results from its ability to produce indole-3-acetic acid (IAA), solubilize phosphorus, and fix nitrogen, as indicated by a 35.76% increase in N-NH₄ and a 35.05% increase in available phosphorus (AP). The introduced PGPB altered the rhizobacterial community of rapeseed, increasing the relative abundance of the phylum Proteobacteria and the genus Pseudomonas while decreasing the relative abundance of phylum Verrucomicrobiota (3 weeks after inoculation). Moreover, Proteobacteria were positively correlated with AP, while Verrucomicrobiota were correlated with N-NH₄. At the genus level, Flavobacterium and Pseudomonas were positively correlated with AP, whereas Candidatus Udaeobacter showed a positive correlation with N-NH₄ and a negative correlation with pH. Importantly, the P2A consortium did not significantly affect the diversity of native rapeseed rhizobacteria. These findings suggest that the tested P2A consortium has potential as a biostimulant in rapeseed cultivation.