Bacillus subtilis NBRI-W9 simultaneously activates SAR and ISR against Fusarium chlamydosporum NBRI-FOL7 to increase wilt resistance in tomato

Abstract

Aims The study aimed to determine the pathogenicity of Fusarium species currently prevalent in tomato fields having history of chemical fungicide applications and determine the bio-efficacy of Bacillus subtilis NBRI-W9 as a potent biological control agent. Methods and results Fusarium fungus was isolated from surface-sterilized infected tomato plants collected from fields. Pathogenicity of 30 Fusarium isolates was determined by in vitro and in vivo assays. Following Koch's postulates, F. chlamydosporum (FOL7) was identified as a virulent pathogen. The biological control of FOL 7 by B. subtilis NBRI-W9 (W9) and colonization potential of W9 was established using spontaneous rifampicin-resistant mutants. W9 showed 82% inhibition of FOL7 on dual-culture plate and colonization levels in tomato plants of ̴ 5.5, ̴ 3.3, and ̴ 2.2 log10 CFU/g in root, stem, and leaf tissue respectively. Antagonistic activity was shown by SEM and cell-wall degradative enzymes. W9 reduced FOL7 infection in net-house and field experiments by 60% and 41%, respectively. Biochemical investigation, defense enzymes, defense gene expression analysis, SEM, and field studies provide evidence of hyper-parasitism and induced resistance as the mode of biological control. The study also demonstrates that potent biocontrol agent W9, isolated from Piper, can colonize tomato plants, control fungal disease by inducing ISR and SAR simultaneously, and increase crop yield by 21.58% under field conditions. Conclusions This study concludes that F. chlamydosporum (NBRI-FOL7) is a potent, fungicide-resistant pathogen causing wilt in tomatoes. NBRI-W9 controlled FOL7 through mycoparasitism and simultaneously activated ISR and SAR in plants, providing an attractive tool for disease control that acts at multiple levels.

Beneficial effects of Bacillus mojavensis strain MTC-8 on plant growth, immunity and disease resistance against Magnaporthe oryzae

“…The induction of ISR by biocontrol Bacillus primarily relies on the jasmonic acid (JA) and ethylene (ET) signaling pathways, but pathogen-induced plant systemic acquired resistance (SAR) primarily depends on the salicylic acid (SA) signaling pathway (Durrant and Dong, 2004 ; Klessig et al, 2018 ). ISR and SAR exhibit similar phenotypic features, including the induction of lignin formation, the accumulation of hydroxyproline-rich glycoproteins (HRGPs), the production of pathogenesis-related proteins (PR proteins), phenolic compound accumulation, and activation of host plant defense enzyme activities (Yi et al, 2013 ; Yadav et al, 2024 ).…”