Plant Growth-Promoting and Antifungal Effects of Bacillus spp. Against Alternaria alternata in Cherry Tomato

Abstract Beneficial rhizobacteria, or PGPR, enhance agricultural productivity. The aim of this study was to isolate, identify, and evaluate indigenous rhizospheric Bacillus strains for their plant growth-promoting traits and biocontrol potential in cherry tomato ( Solanum lycopersicum L.) cultivation. Three Bacillus strains ( Bacillus subtilis E‑30, Bacillus thuringiensis F1-32, and Bacillus pumilus G‑33) were isolated from the cherry tomato rhizosphere and identified using morphological, biochemical, and 16S rRNA gene sequence analyses. The isolates were assessed for their plant growth-promoting attributes and antagonistic activity against the pathogenic fungus Alternaria alternata . Greenhouse pot experiments comprising five different treatments demonstrated that the multi-strain bacterial consortium (Treatment E) produced the most pronounced improvements in plant growth parameters. Compared with the uninoculated control, consortium application increased root and stem lengths by 14.3% and 20.5%, respectively, while root fresh weight and relative chlorophyll content (SPAD values) increased by 22.1% and 18.2%. Among the individual strains, B. thuringiensis F1-32 exhibited strong antagonistic activity, inhibiting A. alternata mycelial growth by 46.27% in vitro. Notably, the study highlights the superior performance of a locally derived multi-strain consortium compared to individual inoculations, providing new evidence for the synergistic potential of indigenous Bacillus strains in sustainable tomato production. Overall, the results indicate that these locally adapted Bacillus isolates particularly when applied as a consortium function as effective biostimulants and promising, eco-friendly alternatives to chemical fertilizers and fungicides for sustainable cherry tomato production.