Induced biosynthesis of bioactive secondary metabolites constitutes one of the mechanisms of plant basal innate immunity to
fungal infection. Metabolic changes were studied in rhizomes of Zingiber zerumbet, a wild congener of ginger, after
infection with soft rot-causative necrotrophic phytopathogen, Pythium myriotylum, by gas chromatography-mass spectrometry (GC-MS) analysis.
Infection triggered a considerable alteration in the relative content of
zerumbone and α-
caryophyllene (
humulene) with enhancement in
zerumbone content (81.59%) and that of α-
caryophyllene (11.91%) compared to 9.97 and 1.11%, respectively, in uninfected rhizomes. While
zerumbone is the principal secondary metabolite in Z. zerumbet, α-
caryophyllene is its immediate precursor. Principal component analysis (PCA) identified the correlations between metabolite changes in Z. zerumbet rhizomes and P. myriotylum
infection. Radial diffusion assay with
zerumbone indicated a concentration-dependent P. myriotylum growth inhibition with 93.75% inhibition observed at 700 μg and 50% maximal effective concentration (EC50) value of 206 μg. Scanning electron microscopy (SEM) analysis revealed that the mechanistic basis of
zerumbone's antagonistic action on P. myriotylum growth involved the induction of aberrant morphology including severe hyphal
deformities and membrane disruption. Results are discussed highlighting the critical role played by
sesquiterpenoid zerumbone in affording resistance in Z. zerumbet and could expedite the development of appropriate strategies for biocontrol of Pythium spp., thus reducing the usage of broad-spectrum fungicides.