Morphological characteristics and chemical composition of s Skullcap (Scutellaria lateriflora L.) and Burdock (Arctium lappa L.) cultivated under different conditions

Abstract

Burdock (Arctium lappa L.) and American skullcap (Scutellaria lateriflora L.) are medicinal plants that are highly rich in phytochemicals which contribute towards their therapeutic values. They also possess culinary values as herbal tea. The roots of Burdock are consumed as salad in Europe and Asian continents which are the regions of its origin. Currently, the plant materials of these plants are imported for their medicinal purposes by herbal practitioners and pharmaceutical industries in different countries of the world, including South Africa. However, the cultivation of these plants is lacking in South Africa and Africa as a whole. To achieve consistent supply of quality products and eliminate batch-to-batch variability of plant materials to meet up with the demand. A preliminary study on yield and phytochemical constituents of Arctium lappa L. as influenced by potassium and phosphorous fertilizer application and two different factorial experiments were conducted for Burdock on Takinogawa long cultivar with eight treatments (T1=N423P210K315, T2=N423P280k315, T3=N635P210K315, T4=N635P280K315, T5=N846P210K315, T6=N846P280K315, T7=N1058P210K315 and T8=N1058P280K315 Kg/ha) and five collection times laid out in a completely randomized design, replicated five times under 40% shade net in pot and field experiments. Fertilizer treatments were split into two equal doses at seedling stage and four weeks after transplanting. Data on morphological characteristics and yield were collected and analysed using SAS software. There was a significant (P<0.05) difference across fertilizer treatments on morphological characteristics and time of collection for both pot and field experiments. Significant differences (P<0.05) were also recorded on the yield parameters investigated. Treatment (N635P210 K315 Kg/ha) significantly outperformed the other treatments in the pot experiment. While for the field experiment, treatment (N846P280K315Kg/ha) significantly outperformed the other treatments. Furthermore, phytochemical constituents, antioxidant and anti-inflammatory activities of aqueous and methanol leaf and root extracts of burdock as influenced by fertilizer treatments were assessed. Result of phytochemical screening were fairly rich indicating a positive test for phenols, flavonoids, tannins, saponins and glycosides. Significant differences (p<0.05) were observed on total phenolic content (TPC), total flavonoids content (TFC) and condense tannins (PAC) on both aqueous and methanol leaf and root extracts in both pot and field studies. The nutritional constituents of the burdock root and leaf samples in both pot and field experiments were significant (P<0.05) except for root lipid content for pot experiment and leaf ash content for field experiment which were not significant (P>0.05). For antioxidant activities, 2,2-diphyl-1-picrythydraxyl, Nitric oxide and hydrogen peroxide were significant (p<0.05) for aqueous and methanol leaf and root extracts for pot and field experiments among treatment combinations. Overall, scavenging activity for treatment combinations with a lower level of phosphorous (P210 Kg/ha) recorded a lower IC50 values compared to those with higher level of phosphorous (P280 Kg/ha). Furthermore, anti-inflammatory activity for aqueous and methanol dried root and leaf extracts for pot and field experiments demonstrated significant differences (p<0.05) among treatment combinations. GC-MS analysis of essential oil for burdock root validated a variation in chemical composition among the different treatment combinations. Interestingly, the greatest variation was demonstrated by T7 with a total of 20 compounds identified; followed by T3 with 19 compounds, T4, T5, T6 and T8 with 14compounds while T1 and T2 had 13 compounds. Similarly, a factorial pot experiment was conducted for S. lateriflora with the same procedure and application, but with different treatments (T1=N350P213K213, T2=N350P320K213, T3=N525P213K213, T4=N525P320K213, T5=N700P213K213, T6=N700P320K213, T7=N800P213K213 and T8=N800P230K213 Kg/ha). Fertilizer treatments and time of collection had a significant (p<0.05) effect on the vegetative growth parameters investigated. Significant (p<0.05) effect was also recorded on biomass yield and total flavonoid contents across the different phenological stages. Fertilizer range (N525-N700 with P213-P320 and K213Kg/ha) had the highest influence on growth and yield attributes. Furthermore, phytochemical constituents, antioxidant, and anti-inflammatory activities of aqueous and methanol leaf extracts of American skullcap as influenced by fertilizer treatments were assessed. The results of phytochemical screening were quite rich at a varying degree, demonstrating the presence of flavonoids, tannins, saponins, phenols, alkaloids, terpenoids and steroids. The highest concentration of total phenolic content was recorded at the post flowering stage (41.65%) followed by the pre-flowering stage (33.83%) and the least at flowering stage (24.52%). Also, total flavonoid content recorded the highest concentration at post flowering stage (38.2%), followed by pre-flowering stage (34.2%) and the least at flowering stage (27.6%). However, for condense tannins, the highest concentration was recorded at the pre-flowering stage (38.5%) followed by the post flowering stage (31.2%) and the least at the flowering stage (30.3%). Also, the nutritional constituents of the leaves were significant (P<0.05). The antioxidant and anti-inflammatory activities exhibited in aqueous, and methanol dried leaf extracts had significant (p<0.05) scavenging and anti-inflammatory activities demonstrated by the IC50 values. T5 had the lowest IC50 values for all the antioxidant assays. However, T4 recorded the most ideal anti-inflammatory activity with IC50 value (352.8 μg/ml) for aqueous extract and T7 (834.1 μg/ml) for methanol extract. Overall, treatments with lower supplementary phosphorous (P1=213kg/ha) recorded a higher concentration of total phenolic, flavonoids and condense tannins, ash, and lipid contents than those with higher supplementary phosphorous (P2=320kg/ha). For carbohydrate content, treatments with high supplementary phosphorus had a higher yield response than those with lower supplementary phosphorous.