Department of Horticulture - Research Articles

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    A practical chemometric approach using UPLC–QTOF/MS tool to investigate three varieties of pumpkin species and in vitro bioactivities.
    (Elsevier Ltd., 2021-06-29) Mashitoa, Florence M.; Shoko, Tinotenda; Slabbert, Retha M.; Shai, Jerry L.; Sultanbawa, Yasmina; Sivakumar, Dharini
    The OPLS-DA, the UPLC–QTOF/MS and chemometric approaches were adopted to discriminate the different varieties belonging to three pumpkin species. Furthermore, this study included a comparison of the phenolic metabolites, antioxidant (DPPH, FRAP and ABTS activity), in vitro α-glucosidase and α-amylase activities, and cell cytotoxicity of the leaves of three varieties of pumpkin species (Cucurbita moschata, C. maxima, and C. pepo). Leaves of all three varieties of pumpkin species contained 23 phenolic metabolites. The OPLS-DA, the UPLC–QTOF/MS and chemometric approach showed that genistin was the candidate biomarker responsible for the separation of butternut squash (C. maxima) from the other two species, while 7-methylquercetin-3-galactoside- 6′′ -rhamnoside-3′′′ -rhamnoside separated the Caserta squash (C. pepo) from the other two pumpkin species. Leaves of Green Hubbard (C. maxima) showed the highest antioxidant capacity (FRAP and ABTS activities), while butternut squash (C. moschata) showed the highest DPPH scavenging activity. Leaf extracts of butternut squash (C. moschata) and Green Hubbard (C. maxima) showed higher inhibition of α-glucosidase activity (IC50 18.22 μg mL 1) and α-amylase (IC50 18.11 μg mL 1) activities respectively, with no cytotoxic effect detected. The phenolic metabolites identified herein for the leaves of each variety of pumpkin species can be potential control markers for further standardisation. Leaves of Green Hubbard (C. maxima) provides functional properties for health benefits.
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    In vitro seed germination and seedling performance of Hibiscus coddii subsp. barnardii.
    (Brazilian Society of Floriculture and Ornamental Plants (SBFPO), 2020-09-16) Du Plessis, Helena Jacoba; Nikolova, Vassileva; Kleynhans, Riana; Egan, Bronwyn Ann
    Hibiscus coddii subsp. barnardii is an endemic South African plant species with ornamental potential. The limited plant availability in nature and restrictions on the collection of living plant material (cuttings) for cultivation purposes, necessitated the development of a protocol for in vitro seed propagation to ensure all year-round ex vitro establishment of plants. The effect of culture medium on seed germination and seedling performance was therefore studied. Various types of sterile seed cultures, namely moist filter paper bridges, five different strengths (¼, ½, ¾, full, 1¼) of PGR-free Murashige and Skoog medium (MS) and solid Gelrite® medium (control) were investigated. High germination percentages (85%-98%) were found in all three seed cultures, although seeds germinated on filter paper, Gelrite® and lower strengths (¼, ½, ¾) of MS medium had shorter mean germination times (1.6-2.8 days) than those germinated on full and 1¼ strengths (3.5-4 days) of MS medium. Furthermore, the growth performance of seedlings varied with the strength of MS medium and was best supported on full strength MS medium, whereas ¼ and ½ strength MS media and Gelrite® cultures were detrimental for seedling growth.
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    Investigation towards propagation and cosmeceutical application of athrixia phylicoides DC.
    (Elsevier B.V., 2017-08-01) Kleynhans, R.; Singh, S.; Kishore, N.; Lall, N.
    Bush tea (Athrixia phylicoides DC.) is a South African indigenous plant with a diverse range of medicinal properties. It is a popular plant, frequently known as Boesmans tee (Afrikaans), Mutshatshaila (Venda), Icholocholo (Zulu) and Mohlahlaishi (Pedi) in different localities (Lehlohonolo et al., 2013). This shrub is found in grasslands, forests, bushveld, rocky and sloping habitats of the eastern parts of South Africa (Lerotholi et al., 2017). This attractive bush plant can be grown in open spaces as a filler and works well as a specimen plant in the garden (Araya et al., 2007). Bush tea can flower throughout the year, with the best flowering time being from March to May and is also reliant on climatic and edaphic factors. The plant requires well-drained soil and full sunlight with enough space for branching.
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    Honeybush (Cyclopia spp.) pollen viability and surface morphology.
    (Elsevier B.V., 2019-11-16) Koen, J.; Slabbert, M.M.; Booyse, M.; Bierman, F.
    Genotypes of Cyclopia, used to produce honeybush tea, are being improved through selective breeding for suitability in large-scale cultivation and consistent flavour/aroma qualities. Though high levels of natural fecundity have been reported in honeybush species, attempts at controlled crosses have hitherto resulted in virtually no seed set. While investigating this problem, it was found that many basic questions regarding the specific reproductive physiology of the genus have not been answered. Studies were undertaken to provide the necessary data about sexual reproduction in honeybush species, in support of existing breeding programmes. This paper presents data concerning pollen viability in relation to flower bud stage, storage and pollen surface morphology of C. longifolia, C. maculata and C. subternata. Pollen anthesis and viability (measured as in vitro pollen germination percentage - PGP1) were linked to visual stages of flower bud development. Pollen samples, dried and stored for 540 days at -18 °C, were tested for PGP at intervals (7, 30, 90, 180, 365, 540 days) during the storage period. While there was an overall decrease in PGP over storage time, four genotypes did not have any significant decrease in PGP over time. The effect of media sucrose content (MSC2) (0 25%) on in vitro PGP of honeybush pollen was tested and differences in response were observed between species. Pollen surface morphology was investigated using FE-SEM microscopy and no consistent differences in shape or surface ornamentation were observed between the species, though differences in grain size were observed.
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    Effect of genotype and harvest season on quality characteristics of cyclopia subternata: Phenolic content and sensory profile.
    (Elsevier B.V., 2020-07-10) Mabizela, G.S.; Muller, M.; De Beer, D.; Van der Rijst, M.; Slabbert, M.M.; Joubert, E.; Bester, C.
    Cultivation of selected Cyclopia species, including C. subternata, is the only viable option to ensure that the current growth trajectory of the honeybush industry is maintained. Gaps in honeybush production knowledge still exist, including the optimum harvest season for production of good quality honeybush, as defined by the phenolic content of the leaves, which is related to bioactivity of extracts, as well as the sensory profile of the herbal tea. The aim of this study was to determine the optimal harvest season for achieving the maximum accumulation of phenolic compounds in the leaves of six genotypes (SGD2, SGD3, SGD6, STB1, SHL2, SKB3) under evaluation by the honeybush breeding programme of the Agricultural Research Council. The major phenolic compounds were quantified by HPLC-DAD. Plants were harvested in summer, autumn, winter and spring. The plant material was also processed to determine whether genotype and harvest season affect the sensory profile of honeybush tea as determined by descriptive sensory analysis. Both genotype and harvest season affected the phenolic content of the leaves and the sensory profile of the herbal tea. Overall, the summer harvest delivered the better product. SGD3 emerged as the genotype with the highest total phenolic content of the leaves (p < 0.05), predominantly due to higher accumulation of the benzophenone, 3- b-D-glucopyranosyl-4-O-b-D-glucopyranosyliriflophenone, and xanthones, mangiferin and isomangiferin. However, herbal tea from SGD3 also had a higher intensity of the negative aroma attribute, ‘hay/dried grass’, although not significantly different from SGD2, SHL2 and STB1 (p 0.05). Considering the positive aroma attributes, STB1 had either the lowest or lower intensities (p < 0.05) of ‘fynbos-floral’, ‘apricot jam’, ‘fruitysweet’ and ‘fynbos-sweet’ than the other genotypes. By identifying summer as optimum harvest time, a foundation is laid for screening of more genotypes to expand the genetic pool and to determine the effect of cultivation practices on quality.
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    Effect of genotype and harvest season on quality characteristics of cyclopia subternata: Phenolic content and sensory profile.
    (Elsevier B.V, 2020-07-10) Mabizela, G.S.; Muller, M.; De Beer, D.; Van der Rijst, M.; Slabbert, M.M.; Joubert, E.
    Cultivation of selected Cyclopia species, including C. subternata, is the only viable option to ensure that the current growth trajectory of the honeybush industry is maintained. Gaps in honeybush production knowledge still exist, including the optimum harvest season for production of good quality honeybush, as defined by the phenolic content of the leaves, which is related to bioactivity of extracts, as well as the sensory profile of the herbal tea. The aim of this study was to determine the optimal harvest season for achieving the maximum accumulation of phenolic compounds in the leaves of six genotypes (SGD2, SGD3, SGD6, STB1, SHL2, SKB3) under evaluation by the honeybush breeding programme of the Agricultural Research Council. The major phenolic compounds were quantified by HPLC-DAD. Plants were harvested in summer, autumn, winter and spring. The plant material was also processed to determine whether genotype and harvest season affect the sensory profile of honeybush tea as determined by descriptive sensory analysis. Both genotype and harvest season affected the phenolic content of the leaves and the sensory profile of the herbal tea. Overall, the summer harvest delivered the better product. SGD3 emerged as the genotype with the highest total phenolic content of the leaves (p < 0.05), predominantly due to higher accumulation of the benzophenone, 3- b-D-glucopyranosyl-4-O-b-D-glucopyranosyliriflophenone, and xanthones, mangiferin and isomangiferin. However, herbal tea from SGD3 also had a higher intensity of the negative aroma attribute, ‘hay/dried grass’, although not significantly different from SGD2, SHL2 and STB1 (p 0.05). Considering the positive aroma attributes, STB1 had either the lowest or lower intensities (p < 0.05) of ‘fynbos-floral’, ‘apricot jam’, ‘fruitysweet’ and ‘fynbos-sweet’ than the other genotypes. By identifying summer as optimum harvest time, a foundation is laid for screening of more genotypes to expand the genetic pool and to determine the effect of cultivation practices on quality.
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    Germination characteristics of dimorphic honeybush (Cyclopia spp.) seed.
    (Elsevier B.V., 2016-04-09) Koen, J.; Slabbert, M.M.; Bester, C.; Bierman, F.
    Cyclopia is a genus of leguminous shrubs endemic to the fynbos biome of South Africa. Cyclopia spp. are used to make honeybush tea for which a high market demand has led to the overharvesting of Cyclopia species in the wild. Consequently, it has become important to study the cultivation requirements of honeybush in order to support farmers with the cultivation of this crop. Honeybush seeds are known to have either physical or combinational dormancy upon maturity, depending on the species. The plants also produce colour-dimorphic (green and brown), mature seeds in the same pod. A study of honeybush (Cyclopia maculata, Cyclopia genistoides and Cyclopia subternata) seed anatomy was carried out using light and dissection microscopy. It is hypothesized that seed physical dormancy is attributable to a relatively thick (3.5 μm) cuticular layer of the integument, a layer of macrosclereid cells, and the presence of a hygroscopically activated hilar valve. There is an absence of other structural openings by which moisture may enter the seed. No consistent structural differences were found amongst the three species or their colour-dimorphic seed. Seeds of the same three honeybush species were divided by colour and their germination response to selected variables (scarification, stratification, seed age and germination temperature) was evaluated. Three dormancy-breaking treatments (wet heat, dry heat and microwave energy) were identified as potential alternatives to conventional sulphuric acid scarification. Highest germination percentage of scarified seed for the three species tested was obtained after 3 weeks of cold stratification at 2 °C and incubated at 15 °C. Brown C. subternata seeds stored for three years gave a significantly higher germination percentage than seed stored for one year only. In non-treated seed, brown seeds had a higher germination percentage than green seeds. In treated seed (i.e. scarified and/or stratified), green seeds had a better germination percentage than brown seeds.
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    Antioxidant enzyme activity, proline accumulation, leaf area and cell membrane stability in water stressed Amaranthus leaves.
    (Elsevier B.V., 2014-08-27) Slabbert, M.M.; Krüger, G.H.J.
    Traditional crops are extremely important for food production in low income, food-deficit countries (LIFDCs) where they continue to bemaintained by socio-cultural preferences and traditional uses. Significant potential exists to improve these crops, one of which is to select for improved productivity during moisture stress conditions. Germplasm of Amaranthus tricolor, Amaranthus hypochondriacus and Amaranthus hybridus were subjected to various screening methods to measure metabolic and physiological changes during water stress. The activities of enzymes involved in the oxygen-scavenging system during abiotic stress conditions (superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR)), free proline production, leaf area (LA), cell membrane stability (CMS), leaf water potential (LWP) and relative water content (RWC) were measured in these three amaranth species during induced water stress. This study showed significant differences in metabolic responses during water deficit of the three species tested. Moisture stress and a decrease in RWC and LWP were first experienced in A. hybridus and A. hypochondriacus, followed by A. tricolor. There was an indirect correlation between leaf water status (RWC and LWP), enzyme activity, proline production and leaf area. The combined effect of GR, APX and SOD could ensure higher levels of regulation of the toxic effect of H2O2 which could be associated with drought tolerance in Amaranthus. Distinct differences in onset of proline accumulation and the amount of accumulated in leaves upon induced water stress was noticed for the three amaranth species tested. Proline accumulation during water stress conditions in amaranth seems to be indirect and could possibly have a protective role apart from osmoregulation during stress conditions. This contention is supported by the decrease in leaf area and high cell membrane stability for two of the species tested. This study forms part of a project aimed at the development of improved traditional crops to contribute to food production and quality for subsistence farmers in areas with low precipitation or variable rainfall patterns.
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    Antioxidant activities of co-encapsulated Natal plum (Carissa macrocarpa) juice inoculated with Ltp. plantarum 75 in different biopolymeric matrices after In vitro digestion.
    (MDPI, 2022-07-16) Seke, Faith; Manhivi, Vimbainashe E.; Guerin, Marie; Shoko, Tinotenda; Akinola, Stephen A.; Garcia, Cyrielle; Remize, Fabienne; Slabbert, Retha M.; Sivakumar, Dharini
    Biopolymeric systems that co-encapsulate probiotics, and bioactive compounds ensure timely delivery in the gastrointestinal tract. Cyanidin 3-sambubioside is the dominant anthocyanin in Natal plum (Carissa macrocarpa). This study aims at the co-encapsulation of Natal plum (Carissa macrocarpa) juice inoculated with Lactiplantibacillus plantarum 75 (Ltp. plantarum 75) by freeze-drying using pea protein isolate, maltodextrin, and psyllium mucilage and evaluating their release in vitro. An encapsulation efficiency of >85% was noted in lactic acid bacteria (LAB) survival and anthocyanin content. Freeze-drying produced pinkish-red powder, rich in polyphenols and LAB (>6 Log CFU mL1) after 14 days of storage. Natal plum juice +maltodextrin + pea protein isolate + psyllium mucilage + Ltp. plantarum 75 (NMPeaPsyB) showed the highest LAB population (6.74 Log CFU mL1) with a survival rate of 81.9%. After digestion, NMPeaPsyB and NMPeaPsy had the highest LAB survival (>50%) at 67.5% and 67.5 0.75%, respectively, and the highest bio accessibility of cyanidin 3-sambubioside in Natal plum juice than the other co-encapsulation with other biopolymers. NMPeaPsy and NMPeaPsyB showed phenolic stability in the gastric phase and controlled release in the intestinal simulated phase. The antioxidant activities had strong correlations with cyanidin 3-sambubioside. The results confirmed that microencapsulation is important for improving stability and allowing for the development of functional foods.
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    A comparison of bioactive metabolites, antinutrients, and bioactivities of African pumpkin leaves (Momordica balsamina L.) cooked by different culinary techniques.
    (MDPI, 2022-03-15) Mashiane, Petunia; Shoko, Tinotenda; Manhivi, Vimbainashe; Slabbert, Retha; Sultanbawa, Yasmina; Sivakumar, Dharini
    Prior to consumption, African pumpkin leaves (Momordica balsamina L.) are generally cooked. In this study, the effects of common household cooking methods (boiling, steaming, microwaving, stir-frying) on bioactive metabolites, carotenoids, antioxidant activity, antinutrients and inhibitory effects on -glucosidase and -amylase activities were examined. A set of 14 bioactive metabolites were identified in raw and cooked African leaves using UPLC-QTOF/MS. The results showed that the four different types of household cooking methods had different effects on the bioactive metabolomics profile of African pumpkin leaves. In comparison to raw leaves and leaves cooked in other methods, the concentrations of six phenolic compounds, rutin, crypto chlorogenic acid (4-caffeoylquinic acid), pseudolaroside A, isorhamnetin 3-O-robinoside, quercetin 3-galactoside, and trans-4-feruloylquinic acid, were highest in stir-fried leaves. Of all household cooking methods tested, stir-frying increased the content of lutein, -carotene, and zeaxanthin by 60.00%, 146.15%, and 123.51%, respectively. Moreover, stir-frying African pumpkin leaves increased the antioxidant activity (DPPH and ABTS) and the inhibition of -glucosidase and -amylase. Compared to all four methods of household cooking, stir-frying reduced the antinutritive compounds compared to raw leaves. This work provides useful information to the consumers on the selection of suitable cooking methods for African pumpkin leaves.
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    Changes in antinutrients, phenolics, antioxidant activities and in vitro a-glucosidase inhibitory activity in pumpkin leaves (Cucurbita moschata) during different domestic cooking methods.
    (Springer, 2021-06-07) Mashitoa, Florence M.; Manhivi, Vimbainashe; Slabber, Retha M.; Shai, Jerry L.; Sivakumar, Dharini
    Pumpkin leaves (Cucurbita moschata) were subjected to different household cooking methods (boiling, microwaving, steaming, and stir-frying) to evaluate their effect on antinutrients, phenolic compounds, antioxidant properties (ABTS, and DPPH) and in vitro a-glucosidase activity. All cooking methods studied significantly reduced the antinutrients and antioxidant activities, whilst phenolic compounds p-coumaric and ferulic acids significantly increased. The cooking methods reduced the oxalates by more than 50%, tannins by 47% and phytates by 79.22%. Steaming and boiling resulted in highest concentrations of p-coumaric (195.40 mg kg-1) and ferulic acids (103.90 mg kg-1) compared to other methods. Overall, boiled leaves retained the highest total phenolic compounds, whilst steamed leaves retained the highest antioxidant capacity. Raw pumpkin leaf extracts showed higher in vitro a-glucosidase inhibitory effects than the cooked leaves. Thus, cooking affected the inhibitory effect of in vitro a-glucosidase activity.
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    Seed germination and vegetative propagation of Helichrysumod oratissimum
    (Elsevier B.V., 2023-08-23) Makena, Ivy Masefako; Matsiliza-Mlathi, Babalwa; Kleynhans, Riana
    Helichrysum odoratissimum is a popular indigenous herb of South Africa, well known for its aromaticity. It offers potential as a source of extracts for the development of cosmeceutical products as it has been reported to be a natural antibiotic, and has antifungal, antimicrobial, antioxidant and antiviral properties. In order to be commercialized, a sustainable production system is required to ensure a consistent supply of good quality material. Therefore, the production of H. odoratissimum by seed and stem cutting was evaluated. The interactive effect of different seed priming methods and temperature levels were investigated on germination indices of H. odoratissimum seeds. A randomized complete block design with three replicates was used to evaluate the effect of season, cutting position, rooting hormone and growth media on survival percentage, number of buds, number of leaves, rooting percentage, number of roots per cutting and root length of H.odoratissimum stem cuttings. Data for both aspects was analysed using ANOVA and means with significant differences were separated with a t-test at 5% level of significance. Smoke treated seeds incubated at 20 °Chad a significantly higher germination percentage (91,7%), mean germination rate (0.59) and coefficient velocity of germination (59.5) compared to most other treatments. Almost all factors tested in vegetative propagation significantly affected parameters measured. Apical cuttings taken during autumn resulted in significantly higher survival (78.5) and rooting percentages (71.1%) compared to other seasons. Cuttings planted in a perlite, vermiculite and sand mixture during autumn significantly outperformed all other season/media combinations with regards to rooting percentage (75%). PGR application improved the number of roots obtained significantly in autumn and winter, but not in summer and spring, compared to the control. It was therefore concluded that, for higher seed germination H. odoratissimum seeds must be primed with smoke water and incubated at 1520 °C and cuttings may be taken autumn for higher rooting and survival rates as well as improved root length. A PGR application can be beneficial depending on the type of medium used.
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    Rooting and survival of Lobostemon fruticosus (L) H. Buek stemcuttings as affected by season, media and cutting position.
    (Elsevier B.V., 2018-09-07) Swarts, A.; Matsiliza-Mlathi, B.; Kleynhans, R.
    The eight-day healing bush (Lobostemon fruticosus) belongs to the Boraginaceae family and is one of the oldest medicinal plants used in the Cape by Khoisan and early settlers. The natural populations of L. fruticosus are being destroyed by veld fires and overharvesting, leading to a need for propagation of plant material especially for commercial use. The objective of the study was to investigate the effect of season, plant growth regulator, growth media and cutting position on survival and rooting of L. fruticosus. A randomised complete block design was used with 2 block replications per season and 10 cuttings as an experimental unit. Treatments included four media, three plant growth regulator treatments and two cutting positions. Improved survival and better root quality was observed in cuttings planted in autumn (survival percentage 85.6% and root score 4.3) compared to spring (survival percentage 50.1% and root score 2.3). In autumn, cuttings planted in peat (91.25%) had the best survival percentage, however, only differed significantly from those planted in bark (77.5%), while in spring, cuttings planted in bark (68.33%) had significantly higher survival percentage compared to all other media {peat (52.92%); peat Pol (51.67%) and sand Pol (27.5%). Survival percentage was significantly higher in heel cutting planted in both bark (85.83%) and peat (78.33%) as compared to apical cuttings planted in the same growth media (bark 60% and peat 65.83%). While cuttings planted in peat consistently outperformed most other season- media treatment combinations in autumn an increase in rooting percentage, root length and root quality recorded in cuttings planted in bark during spring. Increased budding was recorded in cuttings planted in spring, except for cuttings planted in the sand Pol media. Survival percentage, rooting percentage, root quality and budding leaves significantly increased in heel cuttings {survival percentage (61.46%); rooting percentage (41.88%); root score (3.25) and budding leaves (58.96%)} planted in spring as compared to apical cuttings {survival percentage (38.75%); rooting percentage (17.08%); root score (1.34) and budding leaves (38.54%)} of the same season. Rooting percentage (66.25%), root length (57.76mm), root score (4.99) and budding leaf percentage were significantly higher in heel cuttings planted in bark as compared to apical cuttings. Application of PGR's produced a significantly better rooting percentage {Dip 'N Grow® (52.66%) and Seradix B® No. 2 (47.81%), significantly longer roots {Seradix B® No. 2 (36.23 mm) and Dip 'N Grow® (35.34 mm)} and a significantly better root quality score {Seradix B® No. 2 (3.64); Dip 'N Grow® (3.62)} compared to the control. Based on the current findings it is therefore recommended that, L. fruticosus stem cuttings can be propagated successfully using heel cutting type, Seradix B® No. 2 or Dip ‘N Grow® as growth regulator application and, coco-peat as growth media if propagating during autumn or bark if propagating during spring.