Employing depolymerised sodium alginate, triacontanol and 28-homobrassinolide in enhancing physiological activities, production of essential oil and active components in Mentha arvensis L

- Irradiated sodium alginates (ISA) enhanced plant growth promoting activities.
- Foliar spray of ISA, TRIA and HBR improved growth, yield and quality of mint.
- Combined treatment (100 ppm ISA + 10−6 M TRIA + 10−7 M HBR) proved to be the best.
- Combined treatment gave maximum content (43.9%) and yield (121.7%) of essential oil.

There is immense need of enhancing the content and yield of active constituents of medicinally important plants in view of their massive demand worldwide. Various phytohormones have proved effective in this regard. Gamma-rays irradiated sodium alginate (ISA), triacontanol (TRIA) and 28-homobrassinolide (HBR) have also proven as potent plant growth promoting substances for a number of agricultural and horticultural crops. Considering the medicinal importance, a pot experiment was conducted to explore the individual as well as combined effect of best foliar doses of ISA, TRIA and HBR on growth, yield and quality of mint (Mentha arvensis L.). The spray of ISA, TRIA and HBR, applied alone on plants, was positively effective. However, the effect of their combined application was much pronounced as compared to that of their individual application; it improved most of the plant growth attributes, physiological and biochemical parameters, herbage yield and the content and yield of active constituents of mint significantly studied at 100 and 120 DAP. Of the seven spray-treatments [(i) Control, (ii) 100 ppm ISA, (iii) 10−6 M TRIA, (iv) 10−7 M HBR, (v) 100 ppm ISA + 10−6 M TRIA, (vi) 100 ppm ISA + 10−7 M HBR, (vii) 100 ppm ISA + 10−6 M TRIA + 10−7 M HBR], 100 ppm ISA + 10−6 M TRIA + 10−7 M HBR proved to be the best. The combined application resulted in the highest content and yield of essential oil (EO) over the control by 42.1 and 43.9% and 114.0 and 121.7% at 100 and 120 DAP, respectively. This combined treatment of plant growth regulators (PGRs) also proved the best, increasing the content of menthol, l-menthone, isomenthone and menthyl acetate by 7.5 and 6.2%, 31.8 and 32.1%, 25.8 and 21.7%, and 40.1 and 37.2%, respectively, over the respective control at 100 and 120 DAP. As compared to the control, it increased the per plant yields of menthol, l-menthone, isomenthone and menthyl acetate by 129.9 and 135.5%, 190.0 and 194.4%, 162.5 and 164.3%, and by 225.0 and 187.5% at 100 and 120 DAP, respectively.