Effect of oligomeric sodium alginate and chitosan on Growth Attributes, Physiology and Essential Oil Composition in Mentha arvensis L. in Northern Himalayas

Mentha is a genus of plants in the family Lamiaceae. It is estimated that 13 to 18 species exist. The oil derived from Mentha is of great economical use. Natural occurring marine polysaccharides such as sodium alginate, chitosan, carrageenan after undergoing depolymerisation by different techniques have shown positive influence on growth, morphological and yield attributes of plants. In this study, the gamma-degraded polysaccharides like sodium alginate and chitosan have been applied to check the effect on growth, physiological and essential oil composition. A pot experiment was conducted to evaluate the influence of different doses of irradiated sodium alginate (ISA) and chitosan on the growth, physiological and biochemical attributes as well as essential oil composition in Mentha arvensis L. A single dose of ISA was used (80 mg L⁻¹) in combination with six doses of irradiated chitosan (20, 40, 60, 80, 100, 120 mg L⁻¹). It was found from the results that the treatment T4 (ISA₈₀+ IC₈₀) proved to be optimum and enhanced most of the growth parameters. The plant height was recorded higher by 16.88%, fresh weight increase by 41.62%, and dry weight by 31.74% over the control, at the treatment T4 (ISA₈₀+ IC₈₀) respectively. Similar trend was noticed while analysing the physiological and biochemical parameters where the total chlorophyll content and carotenoid content was increased by 40.25% and 37.30%. The carbonic anhydrase (CA) activity increased by 16.26 %.Total nitrogen (N) content showed the maximum increase by 27.60% P content by 14.34% and K content by almost 5.01% over the control plants. The combined treatment (ISA₈₀+ IC₈₀) enhanced the oil yield (as revealed by the Gas Chromatography GC/GC-MS (Mass Spectroscopy) analysis) by 2.89% in menthol content, 39.74% in menthol content, Lmenthone content by 80.05%, L-menthone yield by 319.28%, isomenthone content by 31.73%, menthylacetate content by 36.32%, menthylacetate yield by 200% over the control in M. arvensis L.