Functional Characterization of Wheat Seed Endophytic Bacteria Reveals Plant Growth-Promoting Traits and Potential Biocontrol Activity Against Fusarium Pathogens.

Abstract

Seed-associated microbiota are emerging as key determinants of early plant establishment and resilience, yet their functional potential in wheat remains underexplored. Here, we isolated and functionally characterized culturable bacterial endophytes from seeds of Triticum aestivum cvs. Saekeumkang, Baeggang, and Ariheuk to assess plant growth promotion and pathogen suppression. Sixteen bacterial strains, belonging to Pseudomonadota, Actinomycetota, and Bacillota, were identified using 16S rRNA gene sequencing. Functional assays revealed the high prevalence of plant growth-promoting traits, with all isolates producing indole-3-acetic acid and 56.25% exhibiting phosphate-solubilizing activity, whereas siderophore production was restricted to Pseudomonas poae WSSR12. Despite this apparent functional redundancy, in planta assays demonstrated strong strain-specific effects on seedling biomass. Neobacillus cucumis WSSR17 consistently induced the highest increase in fresh weight. In parallel, dual culture assays against multiple Fusarium pathogens revealed that only one isolate, Calidifontibacillus erzurumensis WSSR11, showed consistent antifungal activity across all tested Fusarium strains. Notably, isolates combining multiple functional traits did not always correspond to the strongest growth promotion, underscoring the importance of host-microbe compatibility and trait expression in planta. Collectively, these findings reveal a functionally diverse seed endophytic community with complementary roles in plant growth and disease suppression. We propose that rational selection and combination of complementary strains, particularly N. cucumis WSSR17 (growth promotion), C. erzurumensis WSSR11 (biocontrol), and P. poae WSSR12 (multifunctional nutrient mobilization) could enable the development of targeted, multi-strain bioinoculant strategies for wheat. This study advances our understanding of seed microbiome functionality and provides a foundation for microbiome-informed crop improvement.