Endophytes for Biological Control of Bacterial Diseases in Horticultural Crops: Mechanisms, Translational Constraints and the Case of Pomegranate Blight

Abstract

Bacterial diseases of horticultural crops are difficult to manage because pathogens can multiply rapidly on or within susceptible tissues, exploit wounds and natural openings, persist in propagation material, and respond inconsistently to bactericides under field conditions. Endophytic bacteria offer a biologically distinctive control strategy: unlike transient epiphytes or rhizosphere inoculants, successful endophytes occupy internal plant niches where they may compete with pathogens, release antibacterial metabolites, interfere with virulence, prime host defence and improve plant physiological resilience. This critical narrative review evaluates the evidence for endophyte-mediated control of bacterial diseases in fruit, vegetable and plantation horticulture, with particular emphasis on pomegranate bacterial blight caused by Xanthomonas citri pv. punicae. Literature published from 1990 to 29 May 2026 was identified through accessible scholarly databases, citation chaining and DOI-level verification. Evidence across citrus canker, tomato bacterial spot and speck, kiwifruit canker, tomato bacterial wilt and canker, and pomegranate blight was appraised for endophytic status, experimental design, mechanism, disease suppression, field relevance and biosafety. The strongest general conclusion is that endophytic competence can improve persistence and spatial proximity to infection courts, but endophytic residence alone does not guarantee effective disease control. Antibiosis, lipopeptides, volatile compounds, niche competition and induced resistance are recurrent explanatory mechanisms, yet they are often inferred from correlated assays rather than established causally. Pomegranate represents one of the clearest recent advances: native Bacillus endophytes progressed from in vitro and polyhouse screening to two-season field evaluation, where disease index was reduced substantially. Even so, evidence remains concentrated in a small number of cultivars, locations and seasons, and the effects of formulation, orchard microbiome, application timing, pathogen population diversity and long-term ecological safety are unresolved. Endophytes should therefore be developed as components of integrated disease management rather than treated as stand-alone replacements for sanitation, clean planting material, surveillance and judicious chemical use. A translational framework is proposed that links strain identity, verified colonisation, mechanism, formulation, multi-environment efficacy and biosafety before commercial deployment.