Phosphate concentrations and methionine application affect quantitative and qualitative traits of valerian (Valeriana officinalis L.) under hydroponic conditions

Abstract

Abstract In addition to absorbing water and nutrients, the medicinal plant roots are sometimes responsible for the secondary metabolite production and/or accumulation. Root extension is, therefore, economically important in these plants. Here we used a hydroponic system to investigate the effects of exogenous methionine (Met) and phosphate (PO4) concentration on the biomass production and quality of valerian (Valeriana officinalis L.) root. The plants were grown in a cocopeat-perlite mixture and irrigated with nutrient solutions differed mainly in phosphate concentration (900, 1200, and 1500 μM) for four months. The valerian plants were exposed five times to 400 μM methionine either as foliar or root applications. Elevated phosphate concentration had a negative impact on yield and quality of valerian root, showing a 32 % reduction in root dry weight at 1500 compared with 900 μM phosphate. The maximum accumulation of essential oil (29 μL plant−1) and valerenic acid (11 mg plant−1) were also recorded at the lowest phosphate concentration (900 μM) coincided with the highest Zn absorption by the plants. Irrespective of the phosphate concentration, using Met, particularly in root application improved the measured plant traits. Met supplementation at the lowest phosphate concentration caused a 1.3-fold and 1.6-fold increase in the yield of the essential oil and valerenic acid, respectively. Overall, these findings indicate that an exogenous supply of Met at a relatively low phosphate concentration can considerably increase the yield and quality of valerian roots under hydroponic conditions.