Chitosan Oligosaccharides Promote the Content of Polyphenols in Greek Oregano (Origanum vulgare ssp. hirtum)

Greek oregano is commonly used as a spice and in traditional medicine in Eurasia. The plant is rich in secondary metabolites, such as volatile organic compounds (VOC) and polyphenols. Chitosan oligosaccharides (COS) are used as a plant elicitor. The objectives of this study were to determine the effects of COS on the growth and content of secondary metabolites in Greek oregano. Four COS treatments (50, 200, 500, and 1000 ppm) were used in a field experiment. The 200 and 500 ppm COS treatments promoted plant height growth, whereas 50 and 200 ppm COS upregulated the content of polyphenols significantly (38 and 29%, respectively). The COS treatments induced H2O2 generation in Greek oregano leaves; thus, the effect of H2O2 treatment was studied to investigate the possible role of H2O2 in growth and polyphenol production. A low concentration of H2O2 also promoted plant height growth, but only tendencies to higher polyphenol content were seen.