Optimizing Hydroponic Nutrient Solutions for Enhanced Growth, Root Biomass and Essential Oil Yield in the Endemic Medicinal Herb (Plectranthus vettiveroides)

Abstract

Plectranthus vettiveroides is a valuable medicinal and aromatic plant native to the Western Ghats, known for its essential oil extracted from roots. Its natural populations are vanishing due to habitat distraction. The present study explores hydroponic cultivation as a sustainable alternative and it was conducted at the Saraswathy Thangavelu Extension Centre, Jawaharlal Nehru Tropical Botanic Garden and Research Institute, Puthenthope, Thiruvananthapuram, Kerala, India, between January 2023 and May 2023. Apical shoot cuttings of P. vettiveroides with ~15cm length having four nodes with apical buds and a minimum of two fully expanded juvenile leaves were harvested from 75-day-old field-grown plants and they were hydroponically grown for 70 days in six different nutrient solutions—Hoagland, Cooper, Hewitt, Steiner, Knoop, and a control with distilled water—under ambient greenhouse conditions. Among the tested media, Hoagland solution supported the most vigorous shoot growth, including increased leaf number and branching. Cooper medium showed a notable effect on pigment synthesis, yielding the highest levels of chlorophyll and carotenoids. Early and enhanced root formation was observed in Hoagland and Hewitt media, although prolonged exposure to static conditions led to excessive root elongation and tip browning. Overall, morphological assessments indicated that plants grown in nutrient-rich media exhibited superior growth and biomass accumulation compared to the control. Additionally, a strong positive correlation was observed between root biomass, photosynthetic pigment concentration, and essential oil yield, emphasizing the role of nutrient availability in regulating key physiological traits. Hydroponic cultivation with optimized nutrient media significantly enhances the growth and essential oil production. This method offers a sustainable strategy for large-scale production of root biomass and essential oils, contributing to the conservation of wild populations.