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

The presence of <i>Bacillus subtilis</i> 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 <i>B. subtilis</i> 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 <i>B. subtilis</i> on roots, and the soil degradation of the selected film. Treatments were: seedlings with <i>B. subtilis</i> at two doses (10^6,12 CFU/mL (B6, B12), film without bacteria (P), films with <i>B. subtilis</i> (P1-P16), and untreated (TST). Among the films, formulation 9 (guar gum 0.6%, candelilla wax 0.15%, glycerol 0.15% and <i>B. subtilis</i> 20%, 1 × 10¹²) significantly increased shoot and root biomass and supported higher root colonization of <i>B. subtilis</i> (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.