Evaluation of Root Films with Bacillus subtilis for Establishment and Growth Promotion in Tomato

The presence of Bacillus subtilis on tomato roots contributes to plant growth promotion, which depends on its ability to establish in the roots. Edible-film formulations have emerged as effective carriers for beneficial bacteria. In this study, we evaluated film formulations based on guar gum, glycerol, and candelilla wax incorporating B. subtilis for root application in tomato seedlings to stimulate plant development. Sixteen film formulations were prepared and applied to seedling by dipping root; plants were grown under a 16/8 h photoperiod. At 60 days, growth parameters (plant height, leaf number, chlorophyll content, fresh and dry weights) were measured, along with B. subtilis on roots, and the soil degradation of the selected film. Treatments were: seedlings with B. subtilis at two doses (10^6,12 CFU/mL (B6, B12), film without bacteria (P), films with B. subtilis (P1-P16), and untreated (TST). Among the films, formulation 9 (guar gum 0.6%, candelilla wax 0.15%, glycerol 0.15% and B. subtilis 20%, 1 × 10¹²) significantly increased shoot and root biomass and supported higher root colonization of B. subtilis (2.3 × 10⁷ CFU/g). The film degraded in soil within 15 days, while the inoculant maintained high viability (6.3 × 10⁸ CFU/mL) after 8 months at 4 °C. These results highlight film formulation 9 as a promising bioinoculant for tomato cultivation.