Abstract
Competition for water between agricultural and non-agricultural economic sectors hampers agricultural production, especially in water-scarce regions. Understanding crop responses in terms of yield and quality to irrigation is an important factor in designing appropriate irrigation management for optimal crop production and quality. Pelargonium sidoides DC., often harvested from the wild, is in high demand in the informal market and for commercial formulations. Agricultural production of high-quality materials through cultivation can help reduce pressure on its wild populations. This study aimed at determining the effects of water and nitrogen on P. sidoides yield and metabolite production. The irrigation treatments applied were 30%, 50%, and 70% of an allowable depletion level (ADL), while the nitrogen (N) levels were 0 (control), 50, 100, and 150 kg ha−1. The 30% ADL resulted in a significantly higher biomass and root yield. Nitrogen at 50 and 100 kg ha−1 resulted in a significantly higher biomass yield, compared to the N control. An increase in sugars and citrate cycle components was observed for the well-watered 30% ADL treatment, whereas water-stressed (50% and 70% ADL) treatments increased alanine, aspartate, and glutamate metabolism, increasing levels of asparagine, 4-aminobutyrate, and arginine. The treatments had no significant effect on the root content of esculin, scopoletin, and umckalin. Water stress induced metabolite synthesis to mitigate the stress condition, whereas under no water stress primary metabolites were synthesized. Moreover, cultivation of P. sidoides as a conservation strategy can increase yield without affecting its bioactivity, while providing sustenance for the rural communities.
Highlights
Agriculture is the major user of water resources in many regions of the world
The fresh biomass yield of P. sidoides was significantly increased with the application of N (50–100 kg ha−1 ) and sufficient water application (30% allowable depletion level (ADL))
The study further showed that irrigation could increase the root yield of P. sidoides significantly, while N levels did not have a significant effect on root yield, an increase in total biomass was observed
Summary
Agriculture is the major user of water resources in many regions of the world. In a drought-prone country such as South Africa, allocation of water resources to other economic sectors due to competition for use may impose restrictions on agriculture, unless innovative irrigation management aimed at saving water while maximizing productivity, is introduced [2]. Metabolites 2020, 10, 219 lack or excess of water is a prerequisite for the development of appropriate irrigation management guidelines for optimal production [3]. The yield and composition of secondary metabolites in medicinal plants are influenced by geographical and environmental factors [5]. Secondary metabolites are associated with increased survival, either by coping with unfavourable environmental conditions or by regulating some metabolic processes [6]. Metabolomics comprises the detection of metabolites present within a biological system under specific conditions, providing a phenotypic assessment of the system [7]
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