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Article

Moringa oleifera Lam. Seed Extracts Improve the Growth, Essential Minerals, and Phytochemical Constituents of Lessertia frutescens L.

by
Nana Millicent Duduzile Buthelezi
1,*,
Nontuthuko Rosemary Ntuli
2,
Liziwe Lizbeth Mugivhisa
1 and
Sechene Stanley Gololo
3
1
Department of Biology and Environmental Sciences, Sefako Makgatho Health Sciences University, Medunsa, P.O. Box 235, Ga-Rankuwa 0204, North West, South Africa
2
Department of Botany, University of Zululand, Private Bag X1001, KwaDlangezwa 3886, KwaZulu-Natal, South Africa
3
Department of Biochemistry and Biotechnology, Sefako Makgatho Health Sciences University, Medunsa, P.O. Box 235, Ga-Rankuwa 0204, North West, South Africa
*
Author to whom correspondence should be addressed.
Horticulturae 2023, 9(8), 886; https://doi.org/10.3390/horticulturae9080886
Submission received: 23 June 2023 / Revised: 30 July 2023 / Accepted: 31 July 2023 / Published: 4 August 2023
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Abstract

:
The exploring of biostimulant sources is important for sustainable agriculture. Although all parts of the moringa plant (Moringa oleifera Lam.) are rich in phytohormones and phytochemicals which may be utilised as a potential plant growth enhancer, most attention has been placed on its leaves as a possible biostimulant for enhancing productivity of plants. Little has been reported on moringa seed extract (MSE) as a growth enhancer on medicinal plants. Thus, this study investigated the efficacy of MSE doses (water spray as control, MSE at 2, 4, 6 and 8%) on growth attributes, mineral content and phytochemical compositions of cancer bush plants (Lessertia frutescens L.) grown during the winter–spring and spring–summer seasons of 2021. A gradual increase in growth characteristics, chlorophyll content, phenols and flavonoid contents was recorded in all concentrations of MSE-treated plants compared with controls. Furthermore, all levels of MSE effectively enhanced the concentrations of macronutrients such as calcium, magnesium, phosphorus, nitrogen and potassium as well as micronutrients comprising copper, zinc, iron, manganese and sodium of cancer bush plants relative to untreated plants. Both 6 and 8% MSE concentrations showed high productivity, minerals and phytochemical constituents in cancer bush plants in comparison with 2 and 4% MSE treatments. Overall, the findings of this study demonstrated that, even at low concentrations, MSE can be successfully applied as a biostimulant to improve the growth and biochemical attributes of cancer bush plants.

1. Introduction

Cancer bush (Lessertia frutescens L.) is rich in health-promoting compounds, including antioxidants, amino acids and pinitol [1]. The biological activity of the cancer bush may be due to the presence of L-asparagine, L-canavanine, L-arginine and γ-aminobutyric acid [2]. These phytochemicals could be responsible for the various pharmacological activities, for instance, antiviral, antioxidant, antitumoral, antimicrobial and anti-allergic properties present in the cancer bush [1]. Cancer bush, which has been long utilized in traditional medicine, is commonly employed for treating diverse illnesses, including cardiovascular diseases, cancer, asthma and fever [1,2]. Moreover, cancer bush plays an important role in alleviating health challenges such as malnutrition associated with poverty-stricken communities [3]. Nevertheless, the production of cancer bush is mainly restricted by abiotic factors such as climate change.
Abiotic stresses restraining the cultivation of cancer bush worldwide include soil fertility decline, extreme temperatures, drought, floods and salinity [3,4]. For decades, the use of synthetic fertilizers has been a common practice to enhance crop yield [5]. However, the constant application of chemical fertilisers can acidify the soil as well as leading plant tissues to regularly absorb and accumulate heavy metals, which consequently decreases the nutritional quality of crops [6]. Excessive use of nitrogenous fertilizers degrades water quality through leaching and contamination of ground or surface water, thus disrupting aquatic ecosystems [7]. Additionally, it may have an impact on the increase in troposphere ozone, greater quantities of greenhouse gases that cause climate change, as well as the deterioration of the protective ozone layer in the stratosphere, and is associated with acid rain, among other problematic factors [8]. Ultimately, human beings are also affected by excessive fertilization as harmful components enter the food chain via bioaccumulation [7]. Hence, exploring natural sources of biostimulants for improving the growth of plants could be an alternative technique for promoting sustainable agriculture [9].
Biostimulants are natural growth regulators that promote crop quality traits through improved nutrition efficiency, rhizospheric activities and tolerance to harsh environmental conditions [10]. Moringa (Moringa oleifera Lam.) is rich in plant-growth-enhancing compounds including phytohormones, namely cytokinin, auxins and gibberellins, antioxidants, minerals and nutrients [11,12]. This makes moringa a potential source of biostimulants to enhance plant metabolism and thus promoting resistance to unfavourable environmental conditions [12]. In addition, the presence of essential minerals including potassium (K), phosphorus (P), nitrogen (N) and magnesium (Mg) in moringa plants (aerial parts) may possibly be another method of supplying plants with nutrients, therefore reducing the use of chemical fertilizers [13]. Consequently, moringa can be used as a stimulant to promote growth and quality attributes of various plants. Although limited previous studies have demonstrated that extracts made from moringa leaves improved the yield of various plants [9,10,11,12], the growth-enhancing properties of moringa seeds remain under-explored to date. This study evaluated the influence of moringa seed extracts (MSE) on growth and chemical attributes of cancer bush.

2. Materials and Methods

2.1. Experimental Site

This experiment was carried out and repeated twice successively under the same experimental setup as our previous study [14]. The experiment was conducted in the tunnel (4 m high, 8 m long and 4 m wide) covered with a green photo-selective coloured net (40% shading) at Sefako Makgatho Health Sciences University (SMU), South Africa (latitude: 25°37′8″ S, longitude: 28°1′22″ E and elevation: 1276 m above sea level) during winter–spring and spring–summer seasons of 2021 [14]. The average temperature and relative humidity in the tunnel were 21.08 °C and 43.01%, respectively, during the study.

2.2. Plant Materials

The cancer bush seedlings were purchased from Plant & Palm Kwekery nursery at Akasia, Pretoria, South Africa (latitude: 25°39′50.6″ S, longitude: 28°08′01.1″ E and elevation: 1300 m above sea level). The seedlings were then kept in the tunnel at SMU and watered three times a day with an average of 200 mL tap water per plant for a week. Subsequently, healthy seedlings were transplanted into plastic terracotta pots (40 cm in diameter and 50 cm depth), containing 5 kg of culterra potting soil per pot.
The culterra potting soil was purchased from Builders Express, Pretoria, South Africa (latitude: 25°40′28.49″ S, longitude: 28°6′31.22″ E and elevation: 1305 m above sea level). The culterra potting soil was made from raw organic materials such as COCO peat, forest products and water retentive agents. Culterra potting soil also contained general 2:3:2 (22), lawn 8:1:5 (25), LAN (28%), ammonium sulphate (21%), vita flora 5:1:5 (33) SRN and vital flora 3:1:5 (26) SRN per 30 kg of soil.

2.3. Moringa Seed Extract (MSE) Preparation and Treatments

Moringa seeds were purchased from Afrinest Moringa Farm in Tzaneen, Limpopo, South Africa (latitude: 23°49′15.3″ S, longitude: 30°10′08.7″ E and elevation: 719 m above sea level). The seeds were crushed into a fine powder with a pestle and mortar and were extracted as per our previous study [14] and according to Taha et al. [10], with minor alterations. Each sample of 100 g of powdered seeds was mixed with 1 L 80% aqueous ethanol using a vortex mixer (E-VM-A analogue vortex mixer, United Scientific, Johannesburg, South Africa) for 30 s. Subsequently, the mixture was kept at room temperature for 6 h with constant stirring and then left overnight. Then, the mixture was centrifuged (laboratory centrifuge-TD4C, Hermle Labortechnik, Berlin, Germany) at 4000× g for 30 min and filtered through Miracloth®. Afterwards, the supernatant was mixed with distilled water (v/v) to attain the desired concentrations of 2, 4, 6 and 8% MSE to use as a foliar spray. The extract was then immediately applied or stored in the refrigerator at −20 °C for further use. In order to guarantee the effective absorption of MSE into the leaf tissue, 0.1% (v/v) Tween-20 was added to the foliar spray as a surfactant, whereas the control plants were subjected to a spray of tap water mixed with the identical surfactant at the exact moment of the MSE treatment. The chemical compositions of MSE that were analysed during our previous study [14], including the antioxidant activity determined during the current study, are presented in Table 1.

2.4. Experimental Design and Plant Management

Both trials were carried out using a randomised complete block design (RCBD). Plant spacing was 40 cm with rows 50 cm apart [15]. Pots were set for MSE foliar spray treatment (2, 4, 6 and 8%). Plants not sprayed with MSE were used as controls. The four MSE treatments and controls were replicated 10 times, which was equivalent to 50 pots per experiment. Cancer bush plants were sprayed with MSE once a week after transplanting and at 7-day intervals during the 10 weeks of the experiment. Cancer bush plants were irrigated with an average of 3 L of tap water/plant/day during the experiment. Plants were vertically trellised using a baler twine two weeks after transplanting to support the main stem [14].

2.5. Plant Growth and Biomass Yield Measurement

Plant height was measured at harvest (10 weeks after transplanting) using a measuring tape [9]. Stem diameter was measured with vernier callipers (KG 15, Guilin Guanglu, Macau, China) and results were expressed in millimetres (mm) [16]. At the termination of the experiment (10 weeks after transplanting), biomass, fresh and dry weight of the shoots and roots were weighed with a Mettler Toledo digital balance (±0.01 g) (ME3002T, Labotec (PTY) Ltd., Johannesburg, South Africa) and dried with a laboratory oven (UTD-1295, LabTech, Johannesburg, South Africa) at 50 °C to constant weight to determine shoot and root dry weight [10,17]. Biomass yield was also measured after harvest [14,18].

2.6. Chlorophyll Content

A chlorophyll meter (SPAD-502, NARICHTM, Cape Town, South Africa) was used to measure the chlorophyll content of the freshly enlarged leaf. The measurements were made in accordance with the cancer bush plant’s growth phases, specifically the seedling (2 weeks after transplanting), vegetative (5 weeks after transplanting) and reproductive stage (9 weeks after transplanting). The leaf chlorophyll content of five plants per replicate/treatment was measured and their average values were utilized to provide the SPAD values [10].

2.7. Inorganic Nutrient Contents

Inorganic nutrients such as macronutrients, for instance, Mg, K, P, N and calcium (Ca) and micronutrients including sodium (Na), manganese (Mn), zinc (Zn), iron (Fe) and copper (Cu) of cancer bush shoots were analysed according to Ucar et al. [19]. Plant shoots were oven-dried at 65 °C for 48 h until a consistent weight was attained [19]. Then, 0.5 g of ground sample was processed for nutrient content using the sulfuric and perchloric acid method [18]. Plant N concentration was measured using the Kjeldahl Analyzer (KJA-9830, Bioevopeak, Shandong, China) according to Black et al. [20]. The P concentration was calorimetrically determined at 882 nm with a spectrophotometer (UV-1700, Shimadzu, Johannesburg, South Africa) as per the method of Murphy and Riley [21]. The K, Mg, Ca, Mn, Cu, Fe and Zn contents were evaluated with an optical emission spectrometry (Optima 2000 DV, Perkin Elmer, Johannesburg, South Africa) [20,21].

2.8. Ascorbic Acid

A method reported by Taha et al. [10] was used to measure the ascorbic acid (AA) concentrations in cancer bush plants, with some minor changes. A 1 g sample of matured leaf of cancer bush was extracted using 10 mL of 6% (w/v) trichloroacetic acid. The extract was then diluted with 2 mL of 2% (w/v) dinitrophenylhydrazine and then one drop of 10% (w/v) thiourea in 70% (v/v) ethanol was added. Afterwards, the supernatant was placed in a water bath for 15 min and then left to cool at ambient temperature for 2 h. Subsequently, 5 mL of 80% (v/v) sulfuric acid was added. The absorbance of samples was recorded at 530 nm with an ultra-violet-to-visible spectrophotometer (UV-1700, Shimadzu, Milan, Italy) under dim light. The AA concentration was calculated from a standard curve plotted using known concentrations of AA and expressed as mg g−1 fresh weight.

2.9. Total Phenolic Content

Total phenolic content (TPC) was measured according to the method of Hertog et al. [22], with minor modifications. Samples of 1 g powdered plant material were mixed with 10 mL 99.8% (v/v) methanol and vortexed for 30 s. Subsequently, the mixture was shaken (Orbital shaker 261, Labotec (PTY) LTD, Durban, South Africa) overnight at ambient temperature. Afterwards, the mixture was centrifuged and then filtered through Miracloth® and rinsed with 10 mL of solvent until no colour released. Subsequently, 10 mL portion of acidified (2 M hydrochloric acid) 60% aqueous methanol was added to samples and placed in a thermostatic water bath (HHW 21.600ALL, Labtron, Camberley, UK) at 90 °C for 90 min. After cooling at room temperature, the mixture was filtered through a Miracloth®. The TPC was determined based on the method of Ali et al. [18]. The diluted plant extracts (0.5 mL of 1:10 g mL−1) were combined with Folin–Ciocalteu reagent (5 mL, 1:10 diluted with distilled water) and aqueous sodium carbonate (4 mL, 1 M). The TPC was spectrophotometrically recorded at 765 nm. Gallic acid equivalent (GAE) was used as a standard and the TPC was expressed as mg GAE mg−1 of sample dry weight.

2.10. Total Flavonoid Content

Total flavonoid content (TFC) was assessed using a known methanolic extract used for the quantification of TPC based on a method of Anjum et al. [23], with minor adjustments. Briefly, a 0.5 mL sample extract was mixed with 2 mL of deionized water followed by 150 µL of sodium nitrite. The samples were then set aside for about 5 min. Afterwards, 150 µL of aluminium chloride was added in 1 mL of 1 M sodium hydroxide. Then, its absorbance was measured at 510 nm. The TFC was calculated using a calibration curve technique using quercetin as the standard and expressed as mg quercetin g−1 of sample dry weight.

2.11. Statistical Analysis

The collected data were subjected to analysis of variance (ANOVA) using GenStat statistical software GenStat®, 18.1 edition, VSN International, UK. Means of significant effects were separated using Fisher’s protected least significant differences at a 5% significance level.

3. Results and Discussion

3.1. Plant Growth Attributes

Plant growth attributes were affected by the use of MSE. The application of MSE at all concentrations significantly (p < 0.05) enhanced plant height, stem diameter, shoot dry weight, root dry weight and biomass yield compared to untreated plants (Table 2). These growth characteristics were progressively enhanced with increasing concentrations of MSE foliar application. Cancer bush plants spayed with MSE had significantly (p < 0.05) increased plant hight, stem diameter and shoot dry weight of up to 61.03 cm, 35.37 mm and 21.91 g, respectively, at 8% MSE application compared to corresponding controls (38.95 cm, 20.03 mm and 14.95 g, respectively). Although root dry weight and biomass yield were not significant among all treatments, they were effectively (p < 0.05) increased by foliar application of MSE up to 6.48 g and 801.10 g at 8% level compared to corresponding controls (3.74 g and 592.40 g, respectively). Overall, our findings demonstrated that foliar application of MSE even at low concentrations effectively improved plant growth of cancer bush. This could be due to the presence of essential minerals, antioxidants, phytohormones and other essential nutrients in MSE (Table 1). Similar results were reported by Abdel-Rahman and Abdel-Kader [24] who observed that 2.5% and 5% moringa leaf extract (MLE) effectively increased vegetative growth traits such as plant height, number of branches/plant and plant dry weight of fennel (Foeniculum vulgare Mill.). Similarly, Khan et al. [9] reported that 3% MLE improved growth and yield parameters of wheat crop (Triticum aestivum L.).
The presence of phytohormones makes MSE a vigorous plant growth biostimulant [14]. Cytokinins (CKs) are one of the most important phytohormones in plants. They are significant for several aspects of plant growth and development as well as embryogenesis, preservation of root and shoot meristems and vascular development [9]. They also modulate root elongation, lateral root number, nodule formation and apical dominance and have anti-senescence potential and protective effects in plants [17]. Thus, the enhanced plant growth observed in this study could be due to the phytohormones, for instance, CKs and Indole-3-acetic acid (IAA) in MSE, which are vital signalling molecules for regulating plant growth and development. Auxins, mainly IAA (Table 1) are an important stimulant of plant growth and development, promoting cell division, elongation and differentiation, embryonic development, root and stem tropisms, apical dominance and transition to flowering [25]. Other phytohormones present in MSE (Table 1) include gibberellins (GAs), which promote cell elongation and division and the development of transition phases [26]. They trigger seed development processes including seed germination, release of seed dormancy and adult and juvenile growth phases [25,26]. Moreover, MSE essential minerals such as Ca, P, Cu and Mg (Table 1), make it an effective natural plant growth stimulant. In addition, our findings are also similar to Rashid et al. [27] who demonstrated that the application of 3% MLE effectively improved plant growth and yield of quinoa plants (Chenopodium quinoa Willd.) due to the phytohormones and nutrients present in MLE.

3.2. Chlorophyll Content

The chlorophyll content of cancer bush plants was affected (p < 0.05) by MSE treatment (Table 2). Chlorophyll content of plants gradually (p < 0.05) increased with increasing doses of MSE. However, the impact of MSE differed based on the growth phases of cancer bush plants. Table 2 shows that plants treated with MSE were greener compared to corresponding controls. According to the growth stages of plants, chlorophyll content of young leaves (seedlings) was enhanced in cancer bush plants sprayed with MSE compared to untreated plants. At 8% MSE foliar application, cancer bush plants had higher chlorophyll content (45.88) compared to control (37.74). Nevertheless, there was a progressive reduction in chlorophyll content at vegetative and reproductive stages which could be attributed to the occurrence of leaf senescence in the chloroplast as chlorophyll is degraded and photosynthesis declines [28]. Table 2 also shows that the chlorophyll content of plants at vegetative and reproductive stages significantly (p < 0.05) increased with increasing concentrations of MSE compared to corresponding controls. The increase in chlorophyll content at vegetative and reproductive stages was up to 42.98 and 41.03, respectively, at 8% MSE application compared to corresponding controls (36.16 and 35.20, respectively). These results could be due to the enhanced nutrient uptake and assimilation that amino acids may incur, which stimulate chlorophyll biosynthesis in biostimulant-treated plants in comparison to the control ones [29].
Furthermore, the application of MSE inhibits premature leaf senescence and chlorophyll deterioration which may promote the biosynthesis of chlorophyll contents, thus enhancing photosynthesis in plants [30]. Furthermore, Table 1 shows that MSE is rich in essential minerals such as Mg and Zn. Mg is an essential element found in chlorophyll pigments within the light-absorbing structure of chloroplasts; thus, it plays a crucial role in the process of photosynthetic carbon dioxide absorption [24]. Zinc plays a vital role in various enzymes that facilitate numerous metabolic reactions in plants [24,31]. The role of this element is important in protecting plants from diseases, promoting photosynthesis, maintaining the integrity of cell membranes, synthesizing proteins, forming pollen and increasing the levels of antioxidant enzymes and chlorophyll in plant tissues [31]. The current study corroborates the results of Ali et al. [18], who stated that various levels of MLE effectively increased chlorophyll content of rose geranium plants (Pelargonium graveolens L.) in comparison to controls. Yaseen and Takacs-Hajos [32] stated that the chlorophyll content of lettuce (Lactuca sativa L.) was increased by 6% MLE application compared to untreated plants.

3.3. Inorganic Nutrient Contents

Foliar application of MSE at all levels effectively (p < 0.05) improved inorganic nutrient concentration of cancer bush plants in comparison to plants that had not been treated (Table 3). It was seen that the content of leaf macronutrients such as Ca, Mg, N, P and K, as well as micronutrients including Zn, Fe, Cu, Mn and Na, were significantly (p < 0.05) higher in plants sprayed with MSE as compared with control. Our findings demonstrated that even at low concentrations the application of MSE gradually increased leaf nutrients of cancer bush plants in comparison to control plants. Table 3 shows that higher nutrient contents were obtained at 4, 6 and 8% MSE application compared to corresponding controls. In addition, 2% MSE treatment also increased nutrient concentrations of cancer bush plants compared to controls. This could be due to the phytohormones such as CKs, GAs and IAA and nutrients including vitamins, minerals and antioxidants present in MSE (Table 1) which assist in maintaining a balance in enzyme activation, osmoregulation and the rate of photosynthesis [28]. Enhanced photosynthesis promotes the vegetative growth and productivity of plants [28,32]. This further supports our findings in Table 2, where the application of MSE improved plant growth attributes compared to untreated plants. Furthermore, the increased nutrient content observed in our study could be associated with the fact that MSE enhances diversion of assimilates from the leaf to the seed, making it a valuable supplier of minerals, antioxidants, and various secondary compounds; consequently, it can effectively sustain the mineral levels within plant tissue [27]. Our findings are similar to Hoque et al. [33], Sardar et al. [34] and Rashid et al. [27], who noted that the application of 10, 20 and 20% MLE improved leaf nutrient composition such as Zn, Na, Mg, Ca, N, P and K in brinjal (Solanum melongena L.), stevia (Stevia rebaudiana Bertoni) and quinoa plants and seeds compared to untreated plants.

3.4. Ascorbic Acid

Ascorbic acid (AA) contents of cancer bush plants were gradually (p < 0.05) increased with increasing concentrations of MSE treatment compared to controls (Figure 1). Although AA contents of plants treated with low doses (2 and 4%) of MSE were not significant from each other (3.92 and 4.45 mg/g FW, respectively), they were higher (p < 0.05) compared to controls (2.01 mg/g FW). Similarly, AA concentrations of plants treated with high levels (6 and 8%) of MSE were statistically not different from each other (6.79 and 7.15 mg/g FW, respectively); however, they were significantly (p < 0.05) higher than low doses of MSE and controls (Figure 1). Our findings demonstrated that the application of MSE even at low doses effectively increased AA contents of cancer bush plants in comparison to untreated plants. This increase in AA of cancer bush plants treated with MSE could possibly be related to the vitamins, antioxidants and secondary metabolites found in the extract of moringa seeds [30]. Moreover, Table 1 shows that MSE contains significant amounts of antioxidants, which may have helped to increase the phytochemical attributes in cancer bush leaves [32]. Considering that MSE is rich in vitamin C (Table 1), its foliar spraying treatment increased the endogenous vitamin C or AA levels in cancer bush plants [24]. Nasir et al. [35], Yaseen and Takacs-Hajos [32] stated that the application of 3 and 6% MLE effectively improved phytochemical composition including AA of mandarin fruit (Citrus nobilis Lour × C. deliciosa Tenora) and lettuce compared to the respective controls.

3.5. Total Phenolic Content

Total phenolic content (TPC) of cancer bush plants gradually (p < 0.05) increased with increasing concentrations of MSE treatment in relation to untreated plants. Higher TPC of plants was obtained at 8% (6.89 mg GAE g−1), followed by 6% (6.03 mg GAE g−1 DW), 4% (4.92 mg GAE g−1 DW) and 2% (4.09 mg GAE g−1 DW) MSE application. Untreated cancer bush plants had the lowest TPC of 2.93 mg GAE g−1 DW. These findings demonstrated that all MSE concentrations effectively increased the TPC of cancer bush in comparison to untreated plants. The increase in TPC in MSE-treated plants can be attributed to significant contents of phytohormones and nutrients such as vitamins and minerals in moringa seeds [36]. Moreover, the significant amount of minerals and vitamins present in moringa seeds may directly or indirectly affect the metabolic processes in such a way that it improved the internal TPC in cancer bush leaves [30,34]. Consequently, these attributes help MSE to serve as a growth regulator and a natural antioxidant [27]. Our findings are in agreement with Nasir et al. [35] and Sardar et al. [34], who reported that 3, 10, 20 and 30% MLE application effectively increased the TPC of mandarin fruit and stevia compared to untreated plants. Furthermore, the increased TPC in cancer bush plants treated with MSE could be attributed to high contents of AA in plants (Figure 1). Ascorbic acid acts as a vital redox buffer and a cofactor for enzymes involved in regulating hormone biosynthesis, photosynthesis and the production of other antioxidants such as phenolic compounds [37]. AA also controls cell division and growth and signal transduction [10,37]. This further supports our findings, where MSE application increased AA (Figure 1), thus consequently increasing TPC (Figure 2) and chlorophyll content and growth attributes (Table 2) of cancer bush plants compared to untreated plants.

3.6. Total Flavonoid Content

Similar to the trend of AA (Figure 1), total flavonoid content (TFC) progressively (p < 0.05) increased with increasing MSE application relative to the controls (Figure 3). The higher contents of TFC were observed at 8% (3.52 mg quercetin g−1 DW) and 6% (3.33 mg quercetin g−1 DW) followed by 4% (2.41 mg quercetin g−1 DW) and 2% (2.01 mg quercetin g−1 DW) MSE treatments, respectively. Untreated plants had the lowest TFC of 1.31 mg quercetin g−1 DW. Therefore, the application of MSE as a biostimulant was successful in enhancing TFC of cancer bush plants relative to control. The results observed in the current study are in agreement with Sardar et al. [34], who stated that 10, 20 and 30% MLE effectively increased the TFC of stevia plants compared to untreated plants due to the flavonoids such as quercetin and kaempferol in MLE. The increase in TFC in cancer bush plants treated with MSE could be attributed to several components of moringa seeds including phytohormones, amino acids, antioxidants and crucial nutrient elements that promote the increase in secondary metabolites including TFC [27]. This further supports our findings as the foliar application of MSE effectively increased metabolites such as AA (Figure 1) and TFC (Figure 2), consequently increasing TFC (Figure 3) in cancer bush plants compared to untreated plants. Furthermore, plant phenolic compounds have a variety of functions in plants, including those of antioxidants, structural polymers (lignin), attractants (carotenoids and flavonoids), ultraviolet screens (flavonoids), signalling molecules (salicylic acid and flavonoids), and defence response chemicals (tannins and phytoalexins) which might have possibly increased TFC in cancer bush treated with MSE relative to untreated plants.

4. Conclusions

In conclusion, MSE can be an effective biostimulant due to the presence of osmoprotectants including total free amino acids, free proline and soluble sugars, essential minerals, particularly Ca, Mg, P, Cu and S, antioxidants, mainly vitamins B, C and E, and phytohormones (CKs, GAs and IAA) to improve growth and biochemical compositions of cancer bush. Even at low concentrations, MSE effectively improved plant growth attributes, mineral contents and phytochemical compounds of cancer bush plants. High concentrations of MSE (6 and 8%) yielded better results of plant quality attributes compared to low doses (2 and 4%). Overall, both high and low concentrations of MSE improved growth characteristics, mineral contents and phytochemical composition of cancer bush plants. Therefore, MSE can be applied as an alternative and eco-friendly plant growth stimulant to promote the productivity of medicinal plants. Future studies should examine the biostimulant potential of various plant parts such as roots and twigs of plants such as moringa to enhance plant growth and productivity.

Author Contributions

Conceptualization, N.M.D.B.; methodology, N.M.D.B.; software, N.M.D.B.; validation, N.M.D.B.; formal analysis, N.M.D.B.; investigation, N.M.D.B.; resources, N.M.D.B.; data curation, N.M.D.B.; writing—original draft preparation, N.M.D.B.; writing—review and editing, N.M.D.B., N.R.N., S.S.G. and L.L.M.; visualization, N.M.D.B.; supervision, S.S.G. and L.L.M.; project administration, N.M.D.B.; funding acquisition, N.M.D.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All data are available in the manuscript file.

Conflicts of Interest

The authors declare no conflict of interest.

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Horticulturae 09 00886 g001
Figure 1. Ascorbic acid content of L. frutescens in response to foliar application of M. oleifera seed extract (MSE). Bars (means ± SE, n = 3) with different letters show statistically significant difference at p < 0.05 between MSE concentrations.
Figure 1. Ascorbic acid content of L. frutescens in response to foliar application of M. oleifera seed extract (MSE). Bars (means ± SE, n = 3) with different letters show statistically significant difference at p < 0.05 between MSE concentrations.
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Horticulturae 09 00886 g002
Figure 2. Total phenolic concentration of L. frutescens in response to foliar application of M. oleifera seed extract (MSE). Bars (means ± SE, n = 3) with different letters show statistically significant difference at p < 0.05 between MSE concentrations.
Figure 2. Total phenolic concentration of L. frutescens in response to foliar application of M. oleifera seed extract (MSE). Bars (means ± SE, n = 3) with different letters show statistically significant difference at p < 0.05 between MSE concentrations.
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Horticulturae 09 00886 g003
Figure 3. Total flavonoid concentration of L. frutescens in response to foliar application of M. oleifera seed extract (MSE). Bars (means ± SE, n = 3) with different letters show statistically significant difference at p < 0.05 between MSE concentrations.
Figure 3. Total flavonoid concentration of L. frutescens in response to foliar application of M. oleifera seed extract (MSE). Bars (means ± SE, n = 3) with different letters show statistically significant difference at p < 0.05 between MSE concentrations.
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Table 1. Chemical properties of moringa (Moringa oleifera Lam.) seed extract (MSE; on a dry weight basis).
Table 1. Chemical properties of moringa (Moringa oleifera Lam.) seed extract (MSE; on a dry weight basis).
ComponentUnitValue
Proteing 100 g−130.44 ± 1.11
Total free amino acids 28.11 ± 0.56
Free proline 0.25 ± 0.03
Soluble sugars 10.11 ± 0.37
Vitamin B1mg 100 g−10.12 ± 0.04
Vitamin B2 0.04 ± 0.01
Vitamin B3 0.12 ± 0.04
Vitamin C 2.92 ± 0.16
Vitamin E 490.35 ± 5.47
Calcium (Ca) 35.08 ± 0.13
Magnesium (Mg) 509.12 ± 0.64
Phosphorus (P) 59.96 ± 0.27
Copper (Cu) 4.19 ± 0.59
Sulphur (S) 0.02 ± 0.00
DPPH (antioxidant activity)
Cytokinins (CKs)		%
µg g−1		70.28 ± 0.66
0.94 ± 0.04
Gibberellins (GAs)
Indol acetic acid (IAA)		 0.85 ± 0.01
0.72 ± 0.11
Values are the mean ± SE, n = 3. DPPH; 2,2-diphenyl-1-picryl-hydrazyl-hydrate.
Table 2. Effect of foliar application of M. oleifera seed extract on growth related attributes of L. frutescens.
Table 2. Effect of foliar application of M. oleifera seed extract on growth related attributes of L. frutescens.
MSE (%) Plant Height (cm)Stem Diameter (mm)Shoot Dry Weight (g)Root Dry Weight (g)Biomass Yield/Plant (g)Chl Content (SPAD Value) Seedling StageChl Content (SPAD Value) Vegetative StageChl Content (SPAD Value) Reproductive Stage
Control38.95 ± 0.74 a20.03 ± 0.73 a14.98 ± 0.39 a3.74 ± 0.15 a592.42 ± 39.21 a37.74 ± 2.98 a36.16 ± 0.48 a37.10 ± 0.61 a
250.22 ± 0.57 b20.05 ± 1.09 b20.40 ± 0.56 bc5.10 ± 0.59 ab720.27 ± 23.54 b40.18 ± 1.07 ab38.95 ± 0.94 b39.40 ± 0.48 b
451.22 ± 0.46 b25.05 ± 0.54 b19.99 ± 0.62 b5.71 ± 0.81 b738.71 ± 39.04 b41.08 ± 0.69 abc40.05 ± 0.90 bc40.03 ± 0.70 b
660.22 ± 0.67 c30.01 ± 0.74 c21.40 ± 0.26 bc6.43 ± 0.87 b789.16 ± 11.42 b44.96 ± 2.06 bc42.45 ± 0.91 cd42.13 ± 0.59 c
861.03 ± 1.04 c35.37 ± 1.20 d21.91 ± 0.15 c6.48 ± 0.27 b801.08 ± 14.72 b45.88 ± 1.75 c42.98 ± 0.57 d43.93 ± 0.71 d
LSD = 1.762
p < 0.001		LSD = 2.659
p < 0.001		LSD = 1.541
p < 0.001		LSD = 1.565
p = 0.019		LSD = 88.30
p = 0.004		LSD = 5.522
p = 0.044		LSD = 2.512
p = 0.001		LSD = 1.787
p < 0.001
MSE, moringa seed extract; Chl, Chlorophyll. Means sharing different letter(s) in a column are statistically significant according to Fisher’s least significant difference (LSD) test at p < 0.05, (mean values ± SE, n = 3).
Table 3. Effect of M. oleifera seed extract on mineral contents of L. frutescens leaves.
Table 3. Effect of M. oleifera seed extract on mineral contents of L. frutescens leaves.
MacronutrientsNPKMgCa
MSE (%)(mg/g DW)
Control 33.34 ± 0.46 a5.91 ± 0.58 a10.81 ± 0.52 a4.56 ± 0.62 a30.08 ± 0.58 a
239.44 ± 1.30 b6.94 ± 0.57 ab15.24 ± 0.61 b6.10 ± 0.49 b40.26 ± 0.46 b
444.12 ± 0.99 c7.42 ± 0.69 bc20.25 ± 1.04 c6.68 ± 0.36 bc42.95 ± 0.61 c
648.01 ± 1.06 d8.30 ± 0.42 bc20.94 ± 0.56 c7.12 ± 0.48 cd54.99 ± 0.49 d
848.92 ± 2.05 d8.45 ± 1.28 c25.54 ± 0.49 d7.78 ± 0.29 d55.69 ± 0.48 d
LSD = 3.706LSD = 1.486LSD = 1.808LSD = 0.978LSD = 1.437
p < 0.001p = 0.023p < 0.001p < 0.001p < 0.001
MicronutrientsFeZnCuMnNa
MSE(mg/g DW)
Control 1.19 ± 0.17 a1.18 ± 0.05 a0.77 ± 0.10 a0.92 ± 0.13 a3.40 ± 0.30 a
21.94 ± 0.19 b2.01 ± 0.15 b2.09 ± 0.21 b1.52 ± 0.25 b6.44 ± 0.32 b
42.25 ± 0.41 b2.41 ± 0.10 c2.20 ± 0.11 b2.09 ± 0.06 c6.80 ± 0.11 b
62.52 ± 0.49 bc2.73 ± 0.19 c2.41 ± 0.12 bc2.30 ± 0.14 c7.99 ± 0.23 c
82.94 ± 0.36 c2.75 ± 0.20 c2.69 ± 0.17 c2.39 ± 0.21 c8.01 ± 0.64 c
LSD = 0.615LSD = 0.387LSD = 0.473LSD = 0.558LSD = 1.043
p = 0.002p < 0.001p < 0.001p = 0.001 p < 0.001
MSE, moringa seed extract. Nitrogen, N; phosphorus, P; Potassium, K; Magnesium, Mg; Calcium, Ca; iron, Fe; zinc, Zn; copper, Cu; manganese, Mn; sodium, Na. Means sharing different letter(s) in a column are statistically significant according to Fisher’s least significant difference (LSD) test at p < 0.05, (mean values ± SE, n = 3).
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Buthelezi, N.M.D.; Ntuli, N.R.; Mugivhisa, L.L.; Gololo, S.S. Moringa oleifera Lam. Seed Extracts Improve the Growth, Essential Minerals, and Phytochemical Constituents of Lessertia frutescens L. Horticulturae 2023, 9, 886. https://doi.org/10.3390/horticulturae9080886

AMA Style

Buthelezi NMD, Ntuli NR, Mugivhisa LL, Gololo SS. Moringa oleifera Lam. Seed Extracts Improve the Growth, Essential Minerals, and Phytochemical Constituents of Lessertia frutescens L. Horticulturae. 2023; 9(8):886. https://doi.org/10.3390/horticulturae9080886

Chicago/Turabian Style

Buthelezi, Nana Millicent Duduzile, Nontuthuko Rosemary Ntuli, Liziwe Lizbeth Mugivhisa, and Sechene Stanley Gololo. 2023. "Moringa oleifera Lam. Seed Extracts Improve the Growth, Essential Minerals, and Phytochemical Constituents of Lessertia frutescens L." Horticulturae 9, no. 8: 886. https://doi.org/10.3390/horticulturae9080886

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