Chapter 2: Literature review
2.5. Overview of medicinal plants used in the current study
Eight different medicinal plant species were selected for testing of nematicidal properties and non-phytotoxicity effects. The selected plants are used mainly to treat various diseases by local people in South Africa and Africa as a continent.
Table 2.3. Information on the selected plant species used in the current study.
Common name Scientific name Family Plant part used
Voucher specimens
Pumpkin Cucurbita maxima Cucurbitaceae Seeds -
Bitter almond Prunus africana Rosaceae Leaf NU0090935
Rabassam Pelargonium sidoides Geraniaceae Tuberous roots
NU0088178
Forest croton Croton sylvaticus Euphorbiaceae Leaf NU0090934
Bitter apple Solanum aculeastrum Solanaceae Leaf NU0090937
36 Star-flowered
bitter-tea
Vernonia colorata Asteraceae Leaf NU0088180
Karee Searsia lancea Anacardiaceae Leaf NU0088179
Blue Squill Merwilla plumbea Hyacinthaceae Bulb NU0090936
Figure 2.3. Merwilla plumbea (Lindl.) Speta was previously known as Scilla natalensis Planch.
(https://species.wikimedia.org/wiki/Merwilla_plumbea).
Merwilla plumbea (Lindl.) Speta, commonly known as blue squill, belongs to the family Hyacinthaceae. Its bulbs are used as medicine in South Africa, mainly in KwaZulu-Natal province (Sparg et al., 2002). The warmed bulb is used externally as an ointment for wound healing, treatment of sprains, fractures, boils, and sores, and to draw abscesses. However, the plant is reported to be highly toxic to mammals (Sparg et al., 2002). The nematicidal properties of M. plumbea are known in nematodes that parasitize humans (Sparg et al., 2002). However, their mode of action and degree of phytotoxicity is still largely unknown.
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Figure 2.5. Cucurbita maxima (Pumpkin) fruits and seeds (https://www.diet- health.info/en/recipes/ingredients/in/dg9392-hokkaido-pumpkin).
Pumpkin (Cucurbita maxima) is a cucurbit that is cultivated chiefly for both human and animal consumption. The plant evolved from the European and American continents. However, today it is widely grown in Asia and Africa (Nishimura et al., 2014). In South Africa, only the fleshy part of the fruit is consumed, whereas seeds are also consumed in the eastern part of Africa. The seed extracts contain vitamins, linoleic acid, oleic acid, and microelements (Nishimura et al., 2014). Seeds of Cucurbita spp. are extensively exploited and have been shown to have a significant effect on controlling animal and human nematodes and other ailments, for example, urinal tract disorders (Salehi et al., 2019a). However, there is no documented report on its impact on plant-parasitic nematodes.
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Figure 2.6. Croton sylvaticus (http://pza.sanbi.org/croton-sylvaticus).
Croton sylvaticus is commonly known as “forest fever-berry” and belongs to the family Euphorbiaceae. Its leaves, bark and roots are utilized to treat ailments such as abdominal pains, boils, fever, inflammation, malaria, rheumatism, swellings, and tuberculosis, as well as for ethnoveterinary medicine (Naidoo, 2008; Maroyi, 2017). Furthermore, Maroyi (2017) highlighted the full range of phytochemical properties of C. sylvaticus, revealing the presence of alkaloids, flavonoids, lignin, sterols, and tannins. Furthermore, the species exhibits pharmacological activities such as antibacterial, antifungal, anti-inflammatory, antioxidant, larvicidal, and well-documented effects on the central nervous system. However, there is no documented literature stating evidence of the nematicidal properties of this species.
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Figure 2.7. Prunus africana (https://www.infonet- biovision.org/PlantHealth/MedicinalPlants/Prunus-africana).
Prunus africana belongs to the Rosaceae family, and the species is commonly known as African almond. In 2006, P. africana was assessed and listed as vulnerable on the Red List of South African Plants (Sanbi: http://redlist.sanbi.org/species.php?species=3457-1). Therefore, this species is under protection in KwaZulu-Natal. The bark is overexploited on a large scale due to its medicinal attributes. In South Africa, the bark is used to treat chest pains, whereas in Europe, the bark extracts have become famous for the treatment of benign prostate hypertrophy. The species is also reported to contain lethal and magical properties (Nonjinge, 2006).
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Figure 2.8. Solanum aculeastrum (http://www.ngkenya.com/flora/solanum_aculeastrum.html).
Solanum aculeastrum belongs to the family Solanaceae and is commonly known as goat bitter- apple. The highly bitter fruit of S. aculeastrum is utilized as medicine (fresh, boiled, or burnt) for pain relief in humans and used to treat ringworm in domestic animals (Welman, 2004). The fruits, both mature and immature, contain the poisonous alkaloid solanine (Welman, 2004).
However, there is no documented literature providing evidence of the nematicidal properties of the species.
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Figure 2.9. Searsia lancea (http://www.plantbook.co.za/searsia-lancea/).
Searsia lancea belongs to the family Anacardiaceae and is commonly known as “karee”. The fruit is eaten by birds such as bulbuls, guinea fowl, and francolins. Searsia lancea leaves provide priceless fodder for livestock (Madzinga and Kritzinger, 2020). The tree is also an essential source of shade for livestock in certain regions (Madzinga and Kritzinger, 2020). The bark, twigs, and leaves of S. lancea contain tannins. The fruits are edible and were once used as an essential ingredient of mead or honey beer (Madzinga and Kritzinger, 2020). However, there is no documented literature stating any evidence of S. lancea having nematicidal properties.
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Figure 2.10. Pelargonium sidoides (https://www.agefotostock.com/age/en/Stock-Images/Rights- Managed/SSJ-80081472).
Pelargonium sidoides DC. (African geranium) belongs to the family Geraniaceae, and it is indigenous to the South African region. Its medicinal properties (treatment of upper respiratory tract infections) have been widely exploited by local traditional healers and international pharmaceutical companies since its discovery in 1897 by Charles Henry Stevens, a man who came to South Africa looking for a TB treatment (https://www.acbio.org.za/wp- content/uploads/2015/02/pelargonium-brief.pdf). Today, in South Africa, there are numerous cough remedies derived from P. sidoides active ingredients. The abundance of wild P. sidoides is in question; the crop is listed on the Red Data List as an endangered species with a possibility of extinction due to over-harvesting, habitat conversion for crop cultivation, and habitat degradation due to livestock overgrazing (Raimondo et al., 2009).
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