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Kiwano

Contributor: Aliza Benzioni

Common Names
Scientific Names
Uses
Origin
Crop Status
1. Toxicities
2. Traditional Uses
Botany
Crop Culture
Post Harvest Treatment
1. Marketing
Germplasm
Key References
Selected Experts

Common Names

English: kiwano, melano, African horned cucumber, jelly melon, hedged gourd, horned melon, English tomato
French: metulon

Scientific Names

Species: Cucumis metuliferus E. Mey. ex Naud or ex Schrad

Family: Cucurbitaceae

Uses

Cucumis metuliferus is currently being promoted as a specialty fruit for export to the European and USA market.

Semiarid regions of southern and central Africa (Kalahari desert): mainly Botswana, South Africa, Namibia, Zimbabwe, Malawi and Nigeria. Was introduced to Australia 70 years ago and became a weed there.

Crop Status

C. metuliferus is grown as an ornamental fruit in New Zealand, Kenya, Israel and the USA and its market is expanding. Since the fruits have a long shelf life and retain their decorative appeal for many months at room temperature it can be developed into a major ornamental fruit.

The present commercial cultigene has a rather bland taste which severely limits its potential as an eating fruit. If its eating quality can be improved, mainly by increasing sugar content, acidity, and aroma, it would be marketed as a new fruit.

Toxicities

Cucurbitacines are present in some accessions of Cucumis metuliferus, making it extremely bitter. These compounds are very toxic to mammals, however as they are the most bitter substances known they are also feeding deterrents and very rarely eaten by mammals. The non-bitter comercial cultivars do not contain cucurbitacines and are not toxic.

Traditional Uses

Kiwano fruits are eaten as a supplement by the local population.

Botany

Taxonomy

Cucumis metuliferus is a single species in the Metuliferus group of the Cucumis, having a distinct morphology and being cross-incompatible with other Cucumis species. It has 2n = 24 chromosomes.

Morphology and Floral Biology

The plant is a monoecious, climbing, annual herb, with staminate flowers typically appearing several days before pistillate flowers. The ellipsoid fruit is bright yellow-reddish orange in color when mature and shaped like a short stout cucumber with many blunt thorns on its surface. These seeds are embedded in the mesocarp which is emerald green and consists of juicy, bland-tasting tissue. Parthenocarpic fruits are produced when temperatures are low.

Ecology

Cucumis metuliferus is endemic to the semi-arid regions of southern and central Africa, where it is found at low to medium altitudes along road sides, fallow and abandoned lands and on the fringes of gullies.

Crop Culture

Propagation

Seeding optimum germination temperatures are between 20° and 35°C (68° to 95°F). Germination is delayed at 12°C (54°F), and inhibited at temperatures lower than 12°C or above 35°C. Thus it is recommended to sow in trays and transplant into the field at the two true leaf stage. The best time for transplanting into an open field is in the spring when soil and air temperatures rise to around 15°C (59°F).

Field Practices

General field practices are similar to those for musk melons. Organic manure (around 2 tonnes/ha) may be incorporated before planting. It was found in Israel that without trailing a density of 10,000 plants per hectares gave good yield (over 46 tonnes/ha of fruits, of which more than 60% were export quality). Time from sowing to harvest was three and a half months.

Fertigation was done with 2-liters/hr drippers spaced 0.5 m apart. Water was applied twice a week with amounts calculated to replenish 40% of evapotranspiration measured by a type A pan till first flower stage, and 80% thereafter. It is possible to grow kiwano under nets or in a greenhouse. Under those conditions trailing is necessary, and for greenhouse production bees must be introduced. The use of greenhouses and nets enable the growth of kiwano in two seasons (early spring and autumn) and supply the market with fruits year round.

Pest and Diseases

It was found that kiwano is resistant to several root-knot nematodes, two accessions were found to be highly resistant to water melon mosaic virus (WMV-1), but very sensitive to the squash mosaic virus(SqMV). Some accessions were found to succumb to Fusarium wilt. Resistance to greenhouse white fly was reported. Kiwano was reported to be resistant to powdery mildew, however in Israel powdery mildew as well as the squash mosaic virus(SqMV) attacked kiwano fields and measures had to be taken.

Post Harvest Treatment

Kiwano fruits have a very long shelf life and may keep for several months. Storage temperature affected fruit shelf life, which is considerably longer at 20° or 24°C (68° or 75°F) than at 4°, 8° or 12°C (39°, 46°, or 54°F) (more then three months in 20° to 24°C compared to few weeks in lower temperatures).

The approximate color turning point is 30-40 days from fruit set and at this stage they reach their maximal weight. During the following month the concentrations of reducing sugars and total soluble solids increases and the peel color changes from green through whitish green to yellow and finally to orange. Fruits picked mature green (at about turning point) fail to develop the desirable uniform orange color even after three months in storage. Exposure of mature green fruits to 160 ppm ethylene for 24 hours induces color formation and they turned yellow-orange within afew days. Fruits left to ripen in the field exhibit higher TSS and reducing sugar values than fruits allowed to ripen in storage.

Marketing

The market volume is restricted; supply must be continuous throughout the year: and prices are optimal only for large and homogeneously orange colored fruits. A market for edible kiwano does not yet exist, because the fruit lacks taste. Increasing the sweetness and improving the aroma may give rise to a new product for a large-volume market.

Germplasm

The seedlings derived from the commercial cultigene do not exhibit much variability, however accessions from the wild have a wide phenological variability which can be used for selection and breeding for improved taste, resistances, etc. The North Carolina Regional Station, Ames, Iowa has a collection of cultigenes which were tested for plant vigor, resistance to Fusarium wilt and yield. Accessions are available at gene banks and the FAO.

Seven accessions were tested in Israel: the commercial cultigene, three lines obtained from the FAO, 67868, 67869 and 67870, two collected in the Kalahari desert (77313 and 77151) and one from Botswana.

Significant differences were found in important fruit quality characters between the commercial cultigene and the accession lines. The Botswana and commercial cultigenes had significantly larger fruit (up to twice as large) and fewer thorns than the other accession lines. The commercial line had significantly lower reducing sugar and higher pH than the other accession lines, but some of the accession lines were bitter.

The line from Botswana had large and attractive fruits, with a slightly different shape. Fruits of this line had high acidity and very good aroma. Crosses between the commercial line and the five accessions were performed, and seeds were produced.

Key References

Bates, D.M., Robinson, R.W., and Jeffry, C. (eds). 1990. Biology and utilization of the Cucurbitaceae. Cornell University Press, Ithaca, NY.
Benzioni, A., Mendlinger, S., Ventura, M., and Huskens, S. 1991. The effect of sowing dates and temperatures on germination, flowering and yield of Cucumis metuliferus. HortScience 26:1051-3.
Bruecher, H. 1977. Cucurbitaceae, In: Tropische Nutzpflanzen. Springer Verlag, Berlin. 1977:258-297.
Keith, M.E. and Renew, A. 1975. Notes on some edible wild plants found in the Kalahari. Gemsbok Park. Koedoe 18, 1-12.
Mendlinger, S., Benzioni, A., Huskens, S., and Ventura, M. 1992. Fruit development and postharvest physiology of Cucumis metuliferus Mey., a new crop plant. J. Hort. Sci. 67:489-493.

Selected Experts

Aliza Benzioni, Institutes for Applied Research, Ben-Gurion University of the Negev, P.O. Box 653 Beer-Sheva 84105 Israel; Tel. 07-6461970; Fax: 07-6472984; email: benzioni@bgumail.bgu.ac.il

Dyremple B. Marsh, Lincoln University, 900 Moreau Drive Jefferson City Missouri 65101; Tel: (314)681-5530; Fax: (314)681-5596

Noel D. Vietmeyer, National Research Council, BOSTID, 2101 Constitution Avenue NW, Washington DC 20418; Tel: (202) 334-2692; Fax: (202)334-2660

M. Ventura, The Institutes for Applied Research, Ben-Gurion University of the Negev P.O.Box 653, Beer-Sheva 84105 Israel; Tel: 07-6461916; Fax: 07-6472984

Cohen Yair, Moshav Zofar, Arava Zfonit; Tel: 07-581461

[Contributor: Aliza Benzioni, Institutes for Applied Research, Ben-Gurion University of the Negev]