Biopolymer-based seed biopriming with fungal endophytes suppresses Fusarium wilt and modulates growth in tomato.

Biopolymer-based seed biopriming is an emerging strategy for delivering endophytic fungal biocontrol agents while maintaining seed viability and fungal persistence, yet the compatibility of carrier matrices with dark septate endophytes (DSE), and the potential of this fungal group against Fusarium oxysporum f. sp. lycopersici (FOL) in tomato, remain unexplored. Three biopolymer matrices - sodium alginate (SA), gum arabic (GA) and guar gum (GG) - were evaluated as carriers for ten endophytic fungal isolates: Torula sp. (BC01, BC11), Sordaria fimicola (BC06), Clarireedia calopus (BC17, BC18), Trichoderma gamsii (BC20), Clarireedia narcissi (BC34), T. saturnisporum (BC49), T. aggressivum f. sp. europaeum (TA) and T. longibrachiatum (H1). Three imbibition times and four concentrations per matrix were compared, and their effects on seed germination and vigour, fungal propagule viability and entrapment efficiency, persistence during cold storage at 4 °C, and biocontrol efficacy against FOL were assessed relative to substrate inoculation. Imbibition for 15 min gave the highest and most consistent germination and vigour, preserving germination above 80% with SA (0.5-1% w/v) and GA (25-40% w/v). Propagule type determined biopolymer compatibility: spore-producing isolates reached maximum viability with GA at medium-to-high concentrations, whereas microsclerotia-producing isolates were better preserved with SA. BC20 combined with GA was incompatible with the crop, producing no seedling emergence across three independent sowings. Cold storage for 30 days maintained viable fungal loads, with BC49, H1 and TA showing the greatest persistence and BC06, BC20 and BC34 the most pronounced decline; initial entrapment and long-term viability were not correlated. Germination and seedling vigour index remained stable throughout 40 days. Biopriming consistently outperformed substrate inoculation, with BC34 and H1 achieving 100% and 94.1% protection, whereas substrate inoculation with BC01 gave negative protection (-29.4%). Principal component analysis separated both application methods, associating biopriming with greater disease suppression and substrate inoculation with greater biomass accumulation, revealing a trade-off between biocontrol efficacy and growth promotion. Individually optimized biopolymer-endophyte formulations therefore represent a viable strategy for sustainable Fusarium wilt management in tomato, and provide the first evidence that DSE propagules can be encapsulated and delivered by seed biopriming.