Growth performance and changes in the leaf metabolite profile of Moringa oleifera Lam. cultivars grown in an open hydroponic system and harvested at different Frequencies

Abstract

Moringa oleifera Lam. is an important plant species with various uses and applications, being cultivated across the world, with most of the production in Africa and Asia. Among other uses, moringa tree is useful for human and animal nutrition, health, cosmetics, biogas and water purification. The tree is associated with important biological activities, due to presence of various flavonoids, flavonol glycosides, glucosinolates, isothiocynates, phenolic acids, terpenes, sterols, and alkaloids compounds. However, the composition and concentration of bioactive compounds in plants, could be affected by factors such as the growing environment, harvesting practices, climatic factors, etc. The aim of this study was therefore to determine changes in the leaf metabolite profile of three M. oleifera genotypes, namely PKM-1, Indian conventional hybrid and Malawi hybrid due to cultivation systems, harvesting frequencies, harvesting time, seasonal changes and genotypes. Trees of these cultivars were grown in an open hydroponic structure and in the field and leaf material were collected throughout the growing season from October to May. Proton nuclear magnetic resonance (1H-NMR) was used for data acquisition, and multivariate data analysis by means of principal component analysis (PCA), partial least square discriminatory analysis (PLS-DA), and orthogonal partial least square discriminatory analysis (OPLS-DA) were applied to determine the changes in the leaf metabolite profile, and also to identify the spectral features contributing to the separation of samples. Targeted metabolite analysis was used to match the NMR peaks of the compounds with the NMR chemical shifts of the contribution plot. The difference in concentration of the compounds were statistically determined comparing the concentrations of the compounds in the different samples. The results showed differences in the leaf metabolite profile due to effect of cultivation systems, harvesting frequencies, harvesting time, genotypes, and changes in growing seasons. Among the compounds that were affected, were chlorogenic acid, ferulic acid, vanillic acid, wogonin, niazirin, esculetin and gamma-Aminobutyric acid. All these compounds showed an increase in concentration under “low” and “intermediate” harvesting frequencies as compared to “high” harvesting frequency. The concentration level of these targeted compounds was also affected by cultivation system, harvesting time, and by genotypes. These results provide insight into the effect of harvesting frequencies, harvesting time, cultivation system and genotypes on the metabolite profile and associated medicinal activity of M. oleifera leaf materials.