Dual activation of induced systemic resistance and systemic acquired resistance by Bacillus spp. confers suppression of Fusarium wilt and enhances tomato productivity
Abstract
Fusarium oxysporum f. sp. lycopersici-induced Fusarium wilt is a major constraint on tomato production worldwide. Beneficial microorganisms, such as Bacillus spp., represent promising biocontrol agents not only through direct pathogen suppression but also via activation of plant immune responses. In this study, the capacity of five endophytic Bacillus strains to induce systemic acquired resistance (SAR) and induced systemic resistance (ISR) in tomato plants challenged with F. oxysporum f. sp. lycopersici was evaluated. Bacillus strains were applied through seed and root inoculation, and defense responses in roots were monitored using key biochemical markers. The temporal activities of peroxidase (POX), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), and lipoxygenase (LOX) were quantified, along with the accumulation of salicylic acid (SA), jasmonic acid (JA), and ethylene (ET), which are indicative of SA- and JA/ET-mediated signaling pathways. All Bacillus isolates significantly enhanced defense-related enzyme activities and phytohormone levels compared with non-treated controls (P < 0.05). Notably, B. toyonensis EPL1.1.3 and B. atrophaeus EPL1.1.4 elicited the strongest increases in ISR- and SAR-associated enzymes, whereas B. cereus SNE2.2 induced the highest ethylene accumulation, indicating robust JA/ET signaling. This concurrent upregulation suggests that specific Bacillus endophytes can overcome the classical SA-JA antagonism, thereby activating a synergistic dual-defense system. Furthermore, the enhanced oxidative burst, reflected by elevated POX and PPO activities, likely reinforced cell wall defenses and contributed to a significant suppression of disease progression. Collectively, these findings identify B. toyonensis and B. atrophaeus as promising dual-pathway elicitors for the integrated management of Fusarium wilt in tomato.
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DOI: https://doi.org/10.33804/pp.010.01.5855
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