Fractions of radiation-processed chitosan induce growth, photosynthesis and secondary metabolism in Java citronella (Cymbopogon winterianus Jowitt)

Abstract Plant growth-promoting activity of radiation-processed chitosan has been widely investigated by several researchers. Taking a step further, different fractions of irradiated chitosan (ICH), separated by column chromatography, were assessed for their effect on growth, physiology, and yield attributes of Java citronella (Cymbopogon winterianus Jowitt), conducting a pot experiment in the net-house conditions. Structural characterization of ICH was carried out using scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) spectroscopy, and Fourier-transform infrared (FT-IR) spectroscopy. Among various fractions, Fraction 2 of irradiated chitosan (ICH-F2) proved the best for almost all the parameters studied including the growth biomarkers, photosynthesis-allied parameters, enzymatic activities, and yield attributes. Interestingly, the ICH-F2 fraction contained a higher amount of carbonyl group as compared to other fractions. Perhaps, this specialty made the ICH-F2 unique and a potent growth promoter. As compared to the control, ICH-F2 enhanced the chlorophyll content (38.6%), and the activities of carbonic anhydrase (27.7%), nitrate reductase (21.5%), and DXR, i.e., deoxy- d -xylulose-5-phosphate reductoisomerase (45.7%). Application of ICH-F2 also enhanced the essential oil (EO) content (35.4%) and EO yield (120.1%) of Java citronella significantly. GC-MS analysis of EO revealed a significant increase in the contents of major aroma-compounds, viz. citronellal (18.4%) and geraniol (20.5%) simultaneous with a concurrent decrease in citronellol (24.6%) and geranyl acetate (19.3%) in comparison to the control.