Ecological Management of Crown Gall-Affected Soils: Pathogen Reservoirs, Disease-Suppressive Microbiomes, and Helper Consortia

Crown gall remains difficult to manage because pathogenic agrobacteria can persist in soil, rhizosphere niches, infected roots, plant residues, and propagative materials, while repeated wounding creates new infection sites. This review examines how these reservoirs interact with soil and plant-associated microbiota to shape disease recurrence. Crown gall-specific studies show that gall and graft-union communities are spatially structured and identify pathogen competition, opine use, and virulence-related functions as processes that may shape disease-associated microbial assemblages. Evidence from better-characterized suppressive soils further identifies niche occupation, resource competition, bacterial–fungal interactions, and community stability as mechanisms worth testing in crown gall systems. Sanitation, wound protection, and single-strain biocontrol remain central to preventive management in nurseries and perennial production systems, whereas microbiome-based approaches remain complementary and experimental. Evaluation of locally adapted microbial consortia should consider pathogen rebound in infection-relevant niches, persistence of protective microorganisms, functional activity, new gall incidence, soil conditions, and non-target effects. Distinguishing crown gall-specific evidence from cross-pathosystem inference will help define testable mechanisms and appropriate criteria for field evaluation.