Structural re-arrangement of depolymerized sodium alginate enriches peltate glandular trichomes and essential oil production of spearmint

•The present study is the first report in scientific literature regarding effect of irradiated sodium alginate on Mentha spicata L. showing:•Structural-rearrangement was observed using UV–vis and FT-IR spectroscopy.•Increase in the density of peltate glandular trichomes.•Augmentation of growth, physiology and yield of the plant.•Essential oil content and yield was accentuated by 36.0% and 122.6% respectively.•Carvone content was incremented by 18.7% however, limonene content decreased by 15.7%.•An eco-friendly and economical agronomical approach to enhance overall yield of plants like spearmint. Over the past decade, radiation-degraded polysaccharides have been used as regulators of growth and development in several crop plants. In quest of the possible reasons of previously established growth-promotion activity of irradiated sodium alginate (ISA), structural parameters of irradiated and un-irradiated sodium alginate were analysed using Ultraviolet-visible spectroscopy (UV–vis) and Fourier Transform Infrared spectroscopic (FT–IR) studies to develop an understanding of structure-property relationship. Using foliar application, response to graded concentrations of ISA was tested in terms of yield and quality attributes of spearmint (Mentha spicata L.). Among different concentrations of ISA [0 (control), 40, 80, 120 and 160mgL−1], 80mgL−1 proved to be the optimum foliar-spray treatment for most of the parameters studied including peltate glandular-trichomes density, which was increased from 20 to 44mm−2. Measurements made at 150days after planting revealed that foliar application of ISA at 80mgL−1 increased the content and yield of spearmint essential oil (EO) by 36.0 and 122.6%, respectively, in comparison to the control. Compared to the control, gas chromatography mass spectrometry (GC–MS) analysis revealed an increase of 18.7% in the carvone content and a decrease of 15.7% in limonene content of the spearmint EO.