FOLIAR APPLICATION OF DEPOLYMERISED CHITOSAN ENHANCES THE GROWTH AND CONTENT OF POLYPHENOLS AND L-ASCORBIC ACID IN Eucomis autumnalis, AN ORNAMENTAL AND MEDICINAL PLANT

Chitosan and its derivatives are promising plant biostimulants with potentially broad applications in agriculture and horticulture. In this study, we determined the effect of the application method and dose of depolymerised chitosan on morphological characteristics and metabolite levels in Eucomis autumnalis, a medicinal and ornamental plant. Depolymerised chitosan (molecular weight ~154,500 g/mol, number average molecular weight ~22,800 g/mol and degree of deacetylation ~85%) was used at 50 and 100 mg/l by drenching plants or spraying. In general, depolymerised chitosan increased the length of plant leaves and roots, especially at the dose of 100 mg/l, and also increased the fresh weight of leaves, bulbs and roots, with a more potent effect found when depolymerised chitosan was applied as a foliar spray. In addition, spraying the plants with chitosan solution at 50 and 100 mg/l caused a significant increase in the total chlorophyll content, by 55.4% and 42.0%, respectively, and the total polyphenol content, by 77.7% and 59.0%, respectively, compared with the control. On the other hand, the biosynthesis of carotenoids was most favourably affected by the application of 100 mg/l depolymerised chitosan by drenching and 50 mg/l depolymerised chitosan by spraying. Foliar application of depolymerised chitosan led to an increase in leaf L-ascorbic acid content by an average of 36.4%, regardless of the dose. The results suggest that depolymerised chitosan applied as a foliar spray promoted the growth of E. autumnalis and contributed to increased biosynthesis of polyphenols, which may be a future means of obtaining metabolites in this species.