| Summary: | The application of microbe-derived products as natural biocontrol agents to boost systemic disease resistance to virus infections in plants is a prospective strategy to make agriculture more sustainable and environmentally friendly. In the current study, the rhizobacterium <i>Bacillus amyloliquefaciens</i> strain TBorg1 was identified based on <i>16S rRNA</i>, <i>rpoB</i>, and <i>gyrA</i> gene sequences, and evaluated for its efficiency in conferring protection of tomato from infection by <i>Tobacco mosaic virus</i> (TMV). Under greenhouse circumstances, foliar sprays of TBorg1 culture filtrate (TBorg1-CF) promoted tomato growth, lowered disease severity, and significantly decreased TMV accumulation in systemically infected leaves of treated plants relative to untreated controls. TMV accumulation was reduced by 90% following the dual treatment, applied 24 h before and after TMV infection. Significant increases in levels of total soluble carbohydrates, proteins, and ascorbic acid were also found. In addition, a significant rise in activities of enzymes capable of scavenging reactive oxygen species (PPO and POX), as well as decreased levels of non-enzymatic oxidative stress markers (H<sub>2</sub>O<sub>2</sub> and MDA) were observed, compared to untreated plants. Enhanced systemic resistance to TMV was indicated by significantly increased transcript accumulation of polyphenolic pathway (<i>C4H</i>, <i>HCT</i>, and <i>CHI</i>) and pathogenesis-related (<i>PR-1</i> and <i>PR-5</i>) genes. Out of the 15 compounds identified in the GC-MS analysis, 1,2-benzenedicarboxylic acid mono(2-ethylhexyl) ester and phenol, 2,4-bis(1,1-dimethylethyl), as well as L-proline, N-valeryl-, and heptadecyl ester were present in the highest concentrations in the ethyl acetate extract of TBorg1-CF. In addition, significant amounts of n-hexadecanoic acid, pyrrolo [1,2-a] pyrazine-1,4-dione hexahydro-3-(2-methylpropyl)-, nonane, 5-butyl-, and eicosane were also detected. These compounds may act as inducers of systemic resistance to viral infection. Our findings indicate that the newly isolated <i>B. amyloliquefaciens</i> strain TBorg1 could be a potentially useful rhizobacterium for promoting plant growth and a possible source of biocontrol agents for combating plant virus infections.
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