Due to the rising demand for essential oil in the world market, peppermint has gained an important status among aromatic and medicinal plants. It becomes imperative to optimize its performance in terms of the growth, physiological functioning and biosynthesis of specialized metabolites. A factorial randomized pot experiment was performed using three peppermint cultivars (Kukrail, Pranjal and Tushar) and five levels of leaf-applied nitrogen (N), viz. 0 (control), 0.5, 1.0, 1.5 and 2%. The phenological features, biochemical parameters, viability of root cells, stomatal and trichome behavior were assessed at 100 days after transplanting (DAT). The yield-related parameters, viz., herbage yield, essential oil content, menthol content and yield were studied at 120 DAT. The results revealed that increasing the N doses up to 1.5% enhanced all the studied parameters of peppermint, which thereafter (at the dose above 1.5% N) decreased. The variation pattern of the studied parameters was “low-high-low”. Cultivar Kukrail surpassed the two other cultivars Tushar and Pranjal. Among the foliar sprays, the application of 1.5% N increased chlorophyll content and net photosynthetic rate in all three cultivars. Moreover, the essential oil (EO), EO yield and menthol yield of the plant were also increased linearly in all three cultivars as compared with their control plants. Nitrogen application enhanced the trichome size and density of the plants, as revealed through scanning electron microscopy. Furthermore, from the GC-MS studies, the EO content in the studied cultivars increased, particularly in the case of menthol, with the N application. It may be concluded that two sprays of N (1.5%) at appropriate growth stages could be beneficial for improving morphological, physio biochemical and yield attributes of peppermint.

Bistorta amplexicaulis (D.Don) Greene from the family Polygonaceae is an important medicinal plant species. The growing therapeutic use of B. amplexicaulis has led to its population depletion thus requiring its conservation. Herein, an efficient, reproducible and reliable propagation protocol system was established for B. amplexicaulis using nodal segments as explant. Various culture media were tested for the assessment of growth and development of this plant species. On the shoot proliferation and rhizogenesis of regenerated B. amplexicaulis plantlets, the effects of several plant growth regulators (PGRs) were assessed. Direct organogenesis from nodal segments was achieved by culturing the nodal explants on Murashige and Skoog medium supplemented with 2.0 mg·L ⁻¹ 6‐benzylaminopurine (BAP). Shoot multiplication was widely affected by the kind and concentration of PGRs, and the subculturing of in vitro regenerated shootlets on fresh medium. After incubation for 4 weeks at optimum BAP concentration, cultures were transferred to secondary medium with BAP (optimized concentration) supplemented with different auxins (indole acetic acid, indole butyric acid, and naphthalene acetic acid [NAA]). Murashige and Skoog medium enriched with 2.0 mg·L ⁻¹ BAP showed the highest shoot induction response (83% ± 3.61%) with mean shoot number (4.67 ± 1.45) and shoot length of 4.33 ± 1.45 cm. Growth medium fortified with 1.0 mg·L ⁻¹ α ‐ NAA exhibited maximum rhizogenesis with 4.33 ± 0.88 roots and average root length as 5.50 ± 0.76 cm from regenerated B. amplexicaulis shoots. Acclimatized plants of B. amplexicaulis showed 90% survival. The projected protocol may serve as a treasured tool for the rapid and large‐scale multiplication of elite B. amplexicaulis and for germplasm conservation to ensure continuous supply of this plant amid the increasing demand.