Re-discover Some of the Underutilized and Neglected Crops of the World With a View to Broaden our Food Resource Base: Cat's Whisker's

Historical perspective and origins.

This vegetable plant has its origins in tropical Africa and Southeast Asia, and has spread to other tropical and subtropical countries in the Northern and Southern hemispheres (Kokwaro, 1976). Dispersal is by birds or wind when the capsules dehisce. Cat’s whiskers is widely distributed in the drier parts of the world like Asia, Africa, and the Americas (Iltis, 1960, 1967; Kuhn, 1988), where it grows and is regarded as a weed. There are, however, no known varieties or cultivars as yet.

The crop

The natural habitat of C. gynandra is wasteland and arable land with annual species as well as grasslands. The plant has a C4 photosynthetic pathway, which is an adaptation that enables the plant to survive in dry and hot environments. It does well in semi-arid, sub humid and humid climates about 1000 m above sea level (asl). The crop is adapted to many soil types, but does very well in soils fertilized with organic manure.

Cultivation

Cleome gynandra plants are propagated by seeds, which may be sown on seedbeds or broadcast at 30 cm spacing. Seedlings emerge after 6-8 days and do not require transplanting. Thinning can be done after three weeks and the thinnings may be consumed as food.

Cat’s whiskers respond positively to increased soil fertility. Use of farmyard manure, where available, is highly recommended, but inorganic fertilizers may also be used. Generous application of nitrogen fertilizers delays flowering of plants and hence extends leaf-harvesting time. A study on the effect of deflowering showed that it increased leaf yield and quality of C. gynandra plants (Maumba, 1993). Deflowering decreases plant height and increases number of branches per plant and hence leaf yield. Leaf yield of cat’s whiskers increases with increasing plant age, until about the 7th week, when yield begins to decline.

The plants do not have dense foliage and therefore are not able to compete effectively with weeds. It is thus necessary that weeding be done at all times. Weeding is by shallow cultivation or hand pulling and should not damage the plants as this may adversely reduce leaf yield and quality.

When the plants reach a height of about 15 cm, they can be harvested by topping, cutting back to ground level or picking individual leaves or leafy branches at frequent intervals. Harvesting starts 4-6 weeks after seedling emergence and may last 4-5 weeks (Maundu et al. unpublished). Biweekly removal of tender leaves allows regeneration of branches hence increasing yield.

Cumulative yields of up to 30 tons per hectare may be obtained, while seed yields may be about 500 kg per hectare.

Pests and diseases

C. gynandra is attacked by pests like pentatomids (Acrosternum gramineum and Agonoselis nubilis) and their parasitoids, locusts (Schistocera gregaria), nematodes (Meloidgyne species), flea beetles (Phyllotreta mashonana), green vegetable bugs (Nezara species), cabbage sawfly (Athalia species), cotton jassids (Empoasca species) and hurricane bugs (Bagrada species). Attack by these insects is more prevalent during dry periods, and can be effectively controlled by spraying with an appropriate insecticide.
Young seeds may be eaten by weaverbirds (Quelea quelea) and the plant is also host to mildew fungus (powdery mildews Sphaerotheca fuliginea, Oidiopsis taurica and Cercospora uramensis (Atheya and Mathur, 1966; Singh, 1983).

Uses
Several studies on the nutritional value of cat’s whiskers have been conducted and the results have revealed that leaves of this plant could be more nutritious than most exotic leafy vegetables. Results further indicate that the plant responds positively to increased soil fertility, although the harvest index is reduced. The plant’s nutritional value may vary with soil fertility, environment, plant type, plant age and the production techniques. Seeds of C. gynandra were analyzed for crude protein and fatty acid content (Chweya 1990). The crude protein composition ranged from 17.9% to 31.4%. Other nutrients that are contained in C. gynandra include carbohydrates (1.3 – 1.4%), lipids (25.1% - 29.6%) and several amino acids like palmitic, stearic, oleic, linoleic, valine, glutamine among others. The leaves also contain a lot of nutritional mineral elements such as potassium, calcium, magnesium, sodium, phosphorus, iron, zinc and copper. All of these are important for the various metabolic processes for normal functioning of the body.

Throughout Africa, the tender leaves or young shoots are eaten boiled as a potherb, relish or side dish. In East Africa, fresh leaves are used as ingredients in other mashed foods, and the dried leaves are ground and incorporated in weaning foods (Chigumira, 1995).

According to FAO (1990), C. gynandra is important as a leafy vegetable in African countries such as Malawi, Zimbabwe, Cameroon, Nigeria, Botswana, Namibia, Swaziland and South Africa. Leaves of this plant may be crushed to make a concoction that is drunk to cure diseases such as scurvy. In many cultures, boiled leaves are regarded as a medicinal meal. In other communities, leaves are boiled and marinated in sour milk for 2-3 days and eaten as a nutritious meal, which is believed to improve eyesight, provide energy and cure marasmus. It is a highly recommended meal for pregnant and lactating women. In some communities, consumption of the vegetable by pregnant women is almost mandatory as its intake eases childbirth and reduces the length of their labour.

Many medicinal uses of C. gynandra exist in different communities. The following are some of the reported uses of cat’s whiskers; a) sap from leaves may be used as an analgesic for headaches, b) sap from pounded young leaves is squeezed into ears, nostrils and eyes to treat epileptic fits and earache, c) a decoction or infusion of boiled leaves or roots is administered to facilitate childbirth in pregnant women, treat conjunctivitis, relieve chest pains and treat severe thread-worm infection.

Other than having medicinal use in human beings, C. gynandra has also been observed to have insecticidal, antifeedant and repellent characteristics (Chandel et al., 1987). Leaves have anti-tick properties that are repellent and acaricidal for larvae, nymphs and adults of ticks. Ticks have been observed to avoid C. gynandra and found to keep 2-5 m away from the plant. Ethanol extract from the plant is toxic to insect pests of cabbages and can thus be used as vegetable insecticide. C. gynandra also acts as forage for bovines and game animals that graze the leaves.

The many uses of C. gynandra make it a versatile species with characteristics that call for its conservation and utilization. In summary these characteristics are; a) it is highly nutritious, b) it can be easily and cheaply cultivated by rural farmers for sale and consumption, c) it can mitigate problems of malnutrition due to lack of vitamins, d) it has many medicinal characteristics which can be harnessed, e) it has insecticidal effects, f) it acts as forage for other animals and g) its seeds are oleaginous and have potential for use as edible oil and animal feed. The list is endless.