Priming of antimicrobial phenolics during induced resistance response towards Pectobacterium carotovorum in the ornamental monocot calla lily

Calla lilies are herbaceous monocotyledonous plants that are highly sensitive to Pectobacterium carotovorum, the causal agent of soft-rot disease. Results demonstrate that, in response to elicitation using plant defense activators, the calla lily produces elevated levels of antimicrobial phenolics and that these compounds contribute to increased resistance against P. carotovorum, as shown by reduced bacterial proliferation in elicited leaves. The polyphenolic nature of the induced compounds was supported by autofluorescence, absorbance spectra, and reaction with Folin-Ciocalteu reagent. Two plant defense activators, Bion and methyl jasmonate, differed in both their capacity to induce accumulation of polyphenols and their resistance against the pathogen. Methyl jasmonate elicitation brought about higher accumulation of free phenolics relative to Bion, suggesting priming of bioactive polyphenols as a principal factor in the calla lily defense against P. carotovorum. To further characterize the nature of induced compounds, two major compounds were collected and identified as swertisin and isovitexin by mass and nuclear magnetic resonance spectroscopies.