Quantification of cyanogenic glycoside content and correlational pest pressure in American elderberry genotypes

Plants have evolved an array of defensive molecules to survive damaging environmental factors. Some plants utilize cyanogenic glycosides that can be rapidly hydrolyzed into highly toxic hydrogen cyanide upon mechanical injury, inducing an unfavorable feeding environment for generalist herbivores in the process termed plant cyanogenesis. Little is known regarding plant cyanogenesis in the rapidly emerging specialty crop American elderberry ( Sambucus nigra subsp. canadensis ). With American elderberry being susceptible to a variety of pests and pathogens, understanding whether cyanogenic glycosides within this species correlate with herbivory and pathogen resistance is crucial for cultivar development. We utilized ultra-high-pressure liquid chromatography coupled to a triple quadrupole tandem mass spectrometer (UHPLC-MS/MS) to evaluate quantitative and qualitative diversity in cyanogenic glycoside content in leaf tissues across a collection of twelve American elderberry genotypes. Total and individual cyanogenic glycoside concentrations were then compared to field performance data to better understand a potential basis for pest and pathogen incidence. Our study revealed that pest pressure is variable among genotypes and that correlations exist between increasing concentrations of both total and individual cyanogenic glycosides within leaves to reduced herbivory and disease damage incidence in field-grown plants. Therefore, leaf cyanogenic glycoside concentration constitutes a potential marker for developing herbivory- and pathogen- resistant American elderberry plants for cultivation. We further report phytochemical evidence that American elderberry produces both aliphatic and aromatic cyanogenic glycosides, which is extremely rare. Additional investigation into the emerging genome sequence of American elderberry provided reinforcing genetic evidence for the presence of both biosynthetic pathways.