Chitosan oligomers and triacontanol trigger growth, photosynthesis, enzyme activity, and essential oil content in field-grown lemongrass

Lemongrass is an industrial crop primarily cultivated for its oil, as lemongrass essential oil (LEO) contains several bioactive constituents with pharmaceutical and cosmetic potential. Although recent decades have witnessed an increase in LEO demand, its production remains relatively low. The present study hypothesised that chitosan oligomers (COS) and triacontanol (TRIA) would increase LEO productivity. For this, foliar sprays of COS and TRIA were applied to the field-grown lemongrass plants. While all the COS and TRIA treatments elicited lemongrass growth and development, the optimum effect was observed with the simultaneous application of COS (80 mg L⁻¹) and TRIA (10⁻⁶ M). This treatment increased plant height, tiller numbers, fresh weight, and dry weight by 32.4 %, 29.2 %, 27.9 %, and 68.3 % over the control. Similar upregulation was observed in chlorophyll (19.1 %), carotenoids (18.2 %), and chlorophyll fluorescence (38.9 %), as well as in carbonic anhydrase (20.5 %) and nitrate reductase (18.3 %) activities. The same treatment also increased the total essential oil content (53.7 %), essential oil yield (95.7 %), citral content (41.67 %), and citral yield (107.7 %) compared to the control. Overall, the combined application of COS (80 mg L⁻¹) and TRIA (10⁻⁶ M) proved the most effective for eliciting general lemongrass physiology. This opens new possibilities for their biotechnological application in other related cash crops. Nonetheless, prospective studies could investigate the molecular mechanism of action and whether these elicitors influence the gene expression of metabolic pathways. This would lead to more targeted applications.