Synthetic Bacterial Consortium Induces Dynamic Shifts in Fungal Community and Alters Microbial Network Topology in Barley Soil Under Field Conditions

Microorganisms are fundamental drivers of soil productivity, mediating nutrient cycling and pathogen suppression. In this study, we evaluated changes in the fungal community in the soil of barley (<i>Hordeum vulgare</i> L.) in a field experiment involving the application of a consortium of <i>Paenibacillus pabuli</i>, <i>Priestia megaterium</i>, <i>Pseudomonas koreensis</i>, and <i>Pseudomonas orientalis</i>. Seed pretreatment and seed pretreatment followed by rhizosphere drenching at different growth stages were implemented. Regarding fungal communities in bulk soil, the rhizospheres of untreated and treated plants were characterized based on full-length ribosomal RNA gene (18S-5.8S-28S) metabarcoding sequencing. Despite the compositional shifts, no statistical differences were observed among the alpha diversity metrics. Seed treatment resulted in long-term, targeted suppression of <i>Fusarium graminearum</i>, <i>Fusarium fujikuroi</i>, <i>Fusarium musae</i>, and <i>Fusarium verticillioides</i> from the booting through flowering and dough development stages, outperforming seed pretreatment followed by rhizosphere drenching. A low-modularity network was observed in the rhizosphere of untreated plants. Seed treatment fostered a highly interconnected and uniform network with low hub-betweenness scores. Rhizosphere drenching of pretreated seeds shifted the network topology toward higher hub-betweenness scores, reducing their connectivity by up to 10% in the rhizosphere and bulk soil. These findings provide a framework for optimizing the soil ecosystem for sustainable agriculture.