Evaluating the effects of garlic extract and Bacillus subtilis on tomato growth and bacterial wilt control

Bacterial wilt, caused by Ralstonia solanacearum, is a devastating disease affecting worldwide tomato production. This study investigated the efficacy of garlic crude extract, Bacillus subtilis, and a combination of the two in managing bacterial wilt and promoting the growth of tomato plants. A randomized complete block design was used, with eight treatments: T1 (Ralstonia only), T2 (Ralstonia + Garlic extract), T3 (Ralstonia + B. subtilis), T4 (Ralstonia + Garlic extract + B. subtilis), T5 (Untreated control), T6 (Garlic extract only), T7 (B. subtilis only), and T8 (Garlic extract + B. subtilis). Disease severity, flower number, stem diameter, and plant height were assessed. Physiological parameters, including the photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO₂ concentration, were measured using a Li-Cor 6800 photosynthesis system. The results showed that T4 (Ralstonia + Garlic extract + B. subtilis) had the highest photosynthetic rate, indicating a synergistic effect between garlic extract and B. subtilis in mitigating the impact of Ralstonia. T7 (B. subtilis only) exhibited the highest stomatal conductance and transpiration rate, suggesting that B. subtilis alone enhanced gas exchange and water uptake in healthy plants. Ralstonia infection (T1) (Ralstonia only) resulted in the highest intercellular CO₂ concentration owing to reduced photosynthetic efficiency. Morphological data revealed that Ralstonia infection significantly (p ≤ 0.05) reduced plant height, flower number, and stem diameter compared to untreated controls. T2 (Ralstonia + Garlic extract) and T3 (Ralstonia + B. subtilis) showed moderate improvements in growth parameters compared to T1 (Ralstonia only), while T4 (Ralstonia + Garlic extract + B. subtilis) exhibited the best performance among infected plants. The findings of this study highlight the potential of garlic extract and B. subtilis as biocontrol agents and growth promoters for managing bacterial wilt in tomatoes. Therefore, this study offers an environmentally friendly approach to strengthening tomato crop resilience and productivity against diseases like bacterial wilt.