The Integrated Management of Sugar-Beet Soilborne Diseases Through Rhizosphere Microbiome Strategies: A Critical Review of Agronomic Evidence and Application Gaps.

Soilborne diseases caused by Rhizoctonia solani, Fusarium oxysporum f. sp. betae, Aphanomyces cochlioides, and Pythium spp. constrain sugar-beet production worldwide, with yield losses exceeding 50% in severely affected fields. These pathogens frequently co-occur, yet most biological control and microbiome studies address them individually, and recommendations from model crops often fail to translate to sugar beet's distinctive root biology and rotation systems. This critical review synthesises evidence on the rhizosphere microbiome as a plant protection resource, organising the literature by agronomic applicability: crop rotation, organic amendments, soil physicochemical management, microbial inoculants and synthetic communities, and microbiome-informed breeding and diagnostics. For each strategy, we state the evidence directness (direct sugar-beet field trials, greenhouse data, cross-crop extrapolation, or mechanistic inference) and evaluate the gap between experimental efficacy and field-ready recommendations. Direct field evidence remains limited: the best-characterised example is Rhizoctonia-suppressive soil linked to non-ribosomal peptide synthetase (NRPS)-producing Pseudomonadaceae and Burkholderiaceae, with 2,4-DAPG-producing Pseudomonas populations also being correlated with disease suppression in sugar-beet seedlings, plus one integrated fungicide-biocontrol field trial. We identify multi-pathogen challenge experiments, multi-site field validation of synthetic communities, and microbiome-informed breeding as priority research gaps. Rhizosphere microbiome management should be integrated into existing disease programmes rather than deployed as a stand-alone replacement.