DOI: https://doi.org/10.5513/JCEA01/27.3.4976

2026, 27 (3)   p. 856-867

Samuel ADESIDA, Blažo LALEVIĆ, Igor KLJUJEV, Jelena JOVIČIĆ-PETROVIĆ, Vera KARLIČIĆ

Abstract

The growing global demand for food production has led to the intensified use of chemical pesticides and mineral fertilisers to maximise crop yields. However, the adverse impact of these chemicals on soil, human health, and crop quality has driven research into sustainable alternatives, such as Plant Growth-Promoting Rhizobacteria (PGPR). This study evaluated the plant growth-promoting (PGP) mechanisms of Bacillus siamensis 32 DfEM and Bacillus amyloliquefaciens 4I through in vitro PGP assays, enzymatic profiling (API ZYM), and a confrontation test against Botrytis cinerea, Fusarium oxysporum, Alternaria sp., and Macrophomina sp. Enzymatic analysis revealed that B. amyloliquefaciens 4I produced six enzymes, while B. siamensis 32 DfEM produced four, including phosphatases, esterases and glycosidases. A zone of inhibition indicated that both strains exhibited a certain level of antifungal activity (30.97% ≤ IR ≤ 50.96%) against the fungal phytopathogens. PGP profiling showed that both isolates could produce ammonia and siderophores. They could neither solubilize inorganic P or Zn on the plate assay nor produce IAA and cellulase. These findings indicate that B. siamensis 32 DfEM and B. amyloliquefaciens 4I possess multiple PGP traits that qualify them as functional PGPR; however, the exhibited traits suggest that they are better suited for biocontrol applications rather than biofertilization. Therefore, it is recommended that additional mechanisms employed by these strains be investigated in greater detail to validate their potential for application as biofungicides for the sustainable and diversified promotion of plant growth.

Keywords

Bacillus amyloliquefaciens, Bacillus siamensis, biocontrol, biofertilization, PGPR, sustainable agriculture

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