The efficacy of microbial-based biostimulants depends on the beneficial microbes' capacity to colonize roots.
Interactions between Bacillus and plants are mediated by diverse metabolites, forming chemical signals that promote both plant growth and defense mechanisms.
Plants synthesize signaling molecules such as organic acids, flavonoids, amino acids, and 1-aminocyclopropane-1-carboxylate (ACC) present in the root exudates.
Bacillus spp. are known to produce a wide range of chemical compounds that act as signal molecules in the rhizosphere and are involved in the modulation of interaction networks, including:
- amino acids
- volatile organic compounds - VOCs (such as 2,3 butanediol),
- lipopeptides (such as surfactin),
- AHL lactonase,
- phytohormones.
Some of the phytohormones known to be produced and released by Bacillus spp. include indole acetic acid (IAA), cytokinins (CKs), gibberellins (GAs), and abscisic acid (ABA).
To mitigate biotic and abiotic stresses, Bacillus bacteria generate cyclic lipopeptides that trigger pathways controlled by jasmonic acid and ethylene, consequently inducing systemic resistance (ISR).
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