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Lost Crops of Africa: Fruits, Volume III
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Lost Crops of Africa: Fruits, Volume III 5 HORNED MELON Horned melon (Cucumis metulifer) is one African fruit that has broken into international commerce, albeit recently, and largely on its looks alone. Until you see one, it really is difficult to appreciate its appearance. One author described it as “an extraordinarily attractive object, simultaneously ugly and beautiful.” Others use words from “cute” to “horrifying.” The unique appearance of today’s horned melon1 is what sells the fruit in increasing numbers worldwide. It has moved beyond curiosity to become fairly common in many upscale markets, often because people like to eat it but more often for its outstanding (and long-lasting) visual qualities. In fact, from a global perspective, horned melon is as much an ornament as a food.2 This surprising success became possible when, in 1982, an adventurous New Zealand couple began cultivating this formerly obscure and essentially wild African fruit. Among its genetic diversity, John and Sharyn Morris found a horned-melon specimen whose fruits were breathtakingly brilliant. They learned how to produce it on a commercial basis. They designed special shipping boxes. And within two years they were exporting their Kiwano® to Japan, where it aroused intense curiosity and sold readily. Soon fruits were being flown to the United States, and then they began arriving by container loads on ships. In all U.S. history, few fruits have been heralded with more hyperbole. One fruiterer who markets over a hundred specialty crops reported that, “Horned melons created more furor and generated more curiosity than any produce item we have helped introduce to the American scene.” Moreover, American farmers started to grow their own. Israel too began commercial production, and now sells fruit to Europe under the name Melano®. It is now also grown along the Mediterranean, and Kenya too is exporting these strange-looking fruits. Most are still shipped by air and, despite the high costs passed on to consumers, they sell. 1 Other common names include jelly melon, métulon (France), and the trademarked names Kiwano® (New Zealand) and Melano® (Israel). 2 Such uses should not be dismissed just because they don’t feed the buyer; the desire for ornamental plants around the house can put good money into a growers’ pocket. After all, the biggest use for the nearly $200 million pumpkin crop in the United States is the hollow Halloween jack-o-lantern; the flower industry is of course worth billions.
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Lost Crops of Africa: Fruits, Volume III To eat a horned melon, you slurp down the vivid green jelly inside. The embedded seeds are soft and normally swallowed at the same time. The taste? Some liken it to lime, others to cucumber, and yet others to a ripe-banana/green-banana cross, or even pomegranate or papaya. Yet others say that it is just like itself and little else; whatever the taste, it grows on a person. Many cultivars have no hint of cucurbit bitterness, and there are good opportunities for improving the overall flavor. The sugar content in some selections has already been doubled. But the primary allure for buyers is still its appearance, both as a whole-fruit decoration or as a beautiful garnish when sliced or diced. Of all the world’s fruits, perhaps none has a better shelf life. The horned melon is a buyer’s dream, sometimes remaining in good condition for 6 months at room temperature even in the tropics. It ships without refrigeration, and in the home, uncut, it can remain a delight for months. Indeed, this is one fruit that must be kept far away from cold. Chilling softens it and makes it susceptible to molds. Cool decreases shelf life.3 The horned melon can also be a seller’s nightmare. Anyone who harvests and packs it must wear gloves because the leaves have needly hairs and the piercing horns on the fruit make it hard to handle. Shippers use nylon brushes to quickly and easily grind down the sharp spikes to rounded nubs, so people can then handle the fruits without stabbing themselves. Even so it is necessary to protect each fruit, for the ground-down projections can still easily spear adjacent fruits unless there is space or a barrier between them. Despite the fact that this money-maker seems like a modern creation from New Zealand, the crop is actually an old one out of Africa. It grows, usually wild and not abundantly, in the warmer climes of southern Africa, and sporadically as far north as Nigeria and Ethiopia and even eastward across the Red Sea. It is a resilient plant, found especially clambering along roadsides and gully fringes as well as on fallowed and abandoned lands. It seems to prefer life among the weeds, and it is commonly overlooked by passersby. Of course, the average wild specimens are not nearly as colorful or distinctive as today’s cultivars, but they are nonetheless unmistakable. In a few parts of Africa, people cultivate this plant in backyard plots, adding its fruits to their salads and other dishes. A few even garden it commercially. It is well represented, for instance, in Malawi’s food markets. Flesh and seeds are eaten raw, and in places the immature fruits are relished like cucumber. Wild fruits are also baked whole like pumpkin, especially across the Kalahari, and are also sun-dried for future use. Nonetheless, in most parts of its native habitat, hardly anyone knows this fruit well. The horned melon has already revealed to the world one rewarding facet of its character. Although this chapter naturally focuses on its surprising 3 Ironically, this has proved to be one of the biggest problems with marketing horned melons in the United States. Supermarket managers are so used to cooling and watering their produce that they cannot break the habit.
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Lost Crops of Africa: Fruits, Volume III A spiky orange oddity crammed with white seeds and vivid green jelly, the horned melon has gone international in recent decades, with several nations shipping it around the world. Back in its African home, the plant is still little used. Seemingly, much more could be made of this strange comestible, one of the few fruits with green flesh when ripe. (© 2005 Monica Palacios-Boyce, Ph.D.) commercial success, readers should not ignore other merits–such as long storage life or resistance to grazing–as they work to bring this plant to its full potential. Currently, essentially only one genetic aspect of horned melon is exploited: its stunning visual appeal. Expanding research on this profitable quality will continue to have payoffs, but visionaries should not let this blind them to other possibilities that are perhaps contained in the untapped biodiversity of this widespread species. Any plant from the same genetic pool as melon and cucumber, yet which has such high tolerance to disease and drought, deserves much greater attention from plant champions. For example, expanding its now-thin flesh could be a goal, perhaps developing a much-needed substitute for disease-bedeviled cucumbers and pickling gherkins. Maybe targeting baking qualities could yield a new, staple-like source of carbohydrates. Even fiercer spines might be emphasized, creating prickly “desert water bottles” that ward off four-legged thieves while holding their moisture for humans. Other innovators might focus on the abundant seed. As with other “lost” fruits, combining imagination, hard work, and a little luck might transform horned melon into an indispensable part of Africa’s own fruit repertoire.
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Lost Crops of Africa: Fruits, Volume III PROSPECTS What future this brilliantly delightful member of the cucumber clan will have is anyone’s guess. In its present form, it may prove a fad that collapses. Many people are disappointed who bite into the fruit anticipating a taste to match the exciting appearance. On the other hand, so many people pay good money for its looks that this alone might motivate clever horticulturists to overcome any perceived culinary constraints. In Africa, Zimbabwe, Botswana, and South Africa already grow sweeter selections. A great tasting horned melon might become a major crop to join its cousins, the melon and watermelon (see chapters in this section). Other routes may also open. In particular, its potential as another “cucumber” seems promising.4 Within Africa Humid areas Uncertain. The plant can thrive under humid conditions, but tropical heat and humidity tend to foster vine growth over fruit set. Dry areas Good prospects, especially when irrigation is available. This is its native habitat and, in Botswana for instance, the plant survives where the rainfall is around 450 mm rainfall. However, it generally needs to be irrigated like melon to get reliable commercial production and to extend the harvest beyond the rainy season. Upland areas Fair prospects. The plant is found naturally occurring to elevations of about 1,000 m. However, the level of success as a fruit crop depends on temperature; uplands whose growing season is cut short by cold may be problematic. Beyond Africa Some types should produce almost anywhere melons thrive (see Chapter 8). In Israel the crop is mainly grown (under irrigation) in the Dead Sea Rift, where heat and other conditions are extreme. USES This fruit is generally eaten raw or transformed into juice. Not everyone likes eating horned melon out-of-hand, but those that do usually cut it lengthwise and serve it “on the half shell.” Another method used by 4 Additional prospects, as well as greater technical detail than possible here, are outlined for horned melon and an increasing number of other African species by Plant Resources of Tropical Africa at www.prota.org; see Preface.
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Lost Crops of Africa: Fruits, Volume III harvesters and packers in New Zealand is to cut off one end, loosen the jelly inside with a knife or clippers, put to mouth, and squeeze. The fruit can also be used in prepared form. There are claims it is, “the best thing ever to happen to a salad”; others believe that it is at its most delicious when simply mixed with plain yoghurt. In France, chefs make sorbets from the pulp. Various “green” drinks have been concocted as well, while pouring the pulp over vanilla ice cream is said to create a special treat, the sweetener in the ice cream bringing out the flavor latent in the fruit. In Botswana. whole ripe fruit are baked in the coals of fires. They are also peeled, split open, sun-dried on both sides, and stored as ready-made preserves. This cucumber relative can also be used as if it were one. Immature fruits are often peeled and eaten raw, tasting like cucumber. Both these and the small, hard, wild forms are also often pickled like gherkins. The leaves—like those of other members of the family—are picked when young, boiled, and eaten like spinach. The leaves have a high concentration of useful minerals, but the presence of antinutritional or toxic components is unknown.5 One contributor notes that they’re “not too tasty,” a frequent criticism of highly nutritious leafy vegetables. NUTRITION The fruits are more nutritious than cucumbers, having notably higher values for most nutrient components. One analysis shows the fruit to be about 90 percent moisture, and containing (on a dry-weight basis) about 10 percent protein, 6 percent fat, and 45 percent carbohydrate, with only about a third to a half the vitamin C of fresh oranges.6 By analogy with its relatives, it seems possible the soft flat seeds–which have a nutty flavor–are rich in both protein and oil. If indeed good for you (see Limitations), these might make them an important foodstuff, especially in malnourished regions. AGRONOMY Although this fruit is produced commercially in New Zealand, France, Israel, Kenya, California, and elsewhere, few details on how to grow it properly are published. The seeds are reportedly hard to germinate, but one of our contributors wrote, “Seeds germinate readily if they are prepared as 5 It was recently reported that mineral concentrations in the leaves exceed 1 percent of plant dry weight, “a much higher value than typical in conventional edible leafy vegetables.” Odhava, B., S. Beekrumb, U. Akulaa, and H. Baijnathc. 2007. Preliminary assessment of nutritional value of traditional leafy vegetables in KwaZulu-Natal, South Africa. Journal of Food Composition and Analysis 20(5):430-435. 6 Arnold, T.H., M.J. Wells, and A.S. Wehmeyer. 1984. Khoisan food plants: taxa with potential for future economic exploitation. Pp. 69-86 in Wickens, G.E., J.R. Goodin, and D.V. Field, eds., Plants for Arid Lands. George Allen and Unwin, London.
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Lost Crops of Africa: Fruits, Volume III follows: “The seed plus jelly is diluted by water and one should let it stand until it begins to smell and is contaminated with fungi (about 5-7 days at room temperature). Then they must be well washed from all jelly, which contains some inhibitory factor for germination. Next step is to dry the seed in air on nets and keep them dry til use.” Some growers report greater production if plants are established in nurseries and then transplanted. At first sight, the growing plant would seem to have no particularly special requirements. Practices used in cultivating squash, melons, or cucumber are likely to bring success. But we are told that Israeli researchers have found that irrigation regimes, fertilizer applications, sowing dates, and stand densities all affect yield and fruit quality considerably. In particular, it was found that fruits growing on the ground suffer blemishes and off-colors. Premium fruits are therefore grown on high trellises. This climber grows well under trees or in thick bush and is said to “leap” onto a fence post or a fence wire in full sun. Israeli farmers grow it using open fields, shade houses (open to the air), and greenhouses (closed), a combination that allows them to supply the fruits year round. The plant is notably resistant to disease and pests, including many of other cucurbits. In the wild its only enemy seems to be a caterpillar that eats its way into fruits lying on the ground. In several experiments with other cucurbits, it proved the one most resistant to nematodes (Meloidogyne incognita and M. javanica). It is also ignored by the pumpkin fly (Dacus bivitattus), a fruit fly that is the bane of curcurbit agriculture in Africa. Nonetheless, diseases can be a problem. Israel has encountered several viruses (notably, zucchini virus), and perhaps bacteria causing “water spots” on the fruit. Also, especially in a wetter climate, fungi can be problematic.7 When grown in greenhouses the crop needs a pollinator, such as bees. Beehives also help when horned melons are grown in the open. Bees, however, are not naturally attracted to the flowers, and visit only when nothing better is around. HARVESTING AND HANDLING Fruits reach full size about 40 days after pollination and the main ripening phase (sugar accumulation and color change) is complete about two weeks later. Harvests exceeding 40 tons per hectare have been reported under ideal conditions. During ripening, fruits exhibit no extra output of carbon dioxide or the ripening hormone ethylene, which in part explains their long shelf life. They are sensitive to ethylene, however, and applying it accelerates ripening, softening the peel and turning it orange in a few days. As already noted, the horned melon is a food-handler’s dream—at least as far as shelf life is concerned. Provided a dry atmosphere is maintained, the fruits will keep for at least six months at temperatures between 17° and 7 “The plants get all the usual things like mildews,” wrote contributor Aliza Benzioni.
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Lost Crops of Africa: Fruits, Volume III 24°C. Shipments from New Zealand remain at sea over three weeks at temperatures of 20-22°C and normally arrive beautifully orange, their prongs firm, and without the loss of a single fruit. The only problem likely to be encountered under normal marketing conditions is a slight dehydration, which may be prevented with a light coat of wax. As noted, refrigeration must be avoided. Chilling kills the taste, softens the skin, and allows even the rounded horns to puncture neighboring fruit. In addition, dividers must be used to separate the layers and keep the fruits from spiking each other. New Zealand exporters separate the layers with cardboard and cushion each fruit in wood wool. Israeli growers pick directly into the final shipping boxes. LIMITATIONS All the new plantings and international movements of a spiky fruit crammed with seeds have caused some observers concern that the horned-melon trade is exposing the world to a rampant, vigorous vine that will become an irrepressible weed. So far there have been no reports of serious outbreaks, but for at least 60 years the plant has been naturalized in tropical Australia and is said to be a nuisance, and at odd times a curse. In Queensland, for instance, the plant is a sometime pest of sugarcane fields and farms,8 although it is not regarded as a weed in South Africa or Botswana.9 It is also considered a nuisance weed at one location in South Carolina (the USDA Vegetable Laboratory near Charleston) but has remained very localized. So far at least, there has been no evidence of calamitous outbreaks. “After years of production we see no problems,” the Morrises reported in New Zealand, a country traumatized by disasters with exotic plants. And Israel has not encountered problems with the crop turning pestiferous.10 And one of our contributors writes “Not in Europe,” either. As noted, the fearsome spines are a hazard. Pickers must wear gloves. In New Zealand, warehouse workers also used protection to push the fruits against brushes and blunt the botanic weaponry, although that process has now been automated.11 As has been also noted, many people initially find the horned melon unappealing as a foodstuff. The appearance certainly can be disconcerting. 8 Weeds of Queensland adds, “it is controlled with herbicides and by disposing of the fruit to prevent reseeding.” Kleinschmidt, H.E. and R.W Johnson. 1977. Weeds of Queensland. Government Printer, Queensland. 9 One of our contributors wrote: “I have never seen it become a pest in Africa. It occurs only in small quantities, and most are widely scattered. The fact that it is sought after by goats and other livestock diminishes its chances of reaching pest status. In any case, it is nutritious, people would eat it if it became common. I have yet to see an edible melon turn into a pest—a ridiculous notion to my mind.” 10 Information from Aliza Benzioni. 11 Sandpaper and even files are also used in smaller operations and home gardens.
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Lost Crops of Africa: Fruits, Volume III One cynic has written that it “is roundly unloved on first acquaintance, and tepidly liked by only a few.” Nonetheless, this exotic orange-spiky edible is continuously gaining adherents, and not everybody dislikes it at first bite. Taste may be improved by selection, mutation, hybridization, or auto-polyploidy, and new selections may be already changing this attitude. Reportedly, even Californians are beginning to enjoy it for its flavor. In selecting wild fruits, it is important they be of the “sweet” type. Some wild plants yield fruits that are bitter, purgative, and emetic. Details of what these off-types contain are incomplete, but the bitterness comes largely from the toxic cucurbitacins and, probably, other compounds common in cucurbits. One contributor to this chapter wrote, “The wild ones in Botswana are seldom, if ever bitter.” Yet, another wrote, “When uncultivated types from Queensland were sold in Australia, the market slumped.” At least some of the plants are daylength sensitive. In temperate zones, they set fruit so late in autumn that they cannot mature before winter strikes. This has been noted in Israel, for example, where it was found that the seeds had to be sown in March or April; sowing in May or June was too late. Although many seeds are unavoidably swallowed while eating the flesh, and they are also reported as edible when eaten alone, their safety needs greater substantiation, especially if the horned melon is to be developed as a melon-seed crop. There are reports that, as in many plants, the sprouting seed produces a toxic substance in its embryo.12 In addition, seeds are traditionally also ground into a fine flour and taken with water as a vermifuge to expel tapeworms or other parasites.13 As noted, the flesh can range from bitter to sweet, and the same is probably true of the seed. NEXT STEPS Although proponents may see horned melon as an international success story, the crop is barely beyond its formative years and its domestication has hardly commenced. The future could see it trail away almost into economic nothingness, but that seems unlikely. It might also see horned melon transformed into a mature and respectable resource, one that perhaps is very different from the often tasteless, spiky oddity common today. Actions likely to help include the following. Breeding Better Fruits Currently, some consumers don’t like eating horned melons. However, improvements are certainly possible. Breeding programs aimed at improving their taste without losing their looks are having a big impact. Already, it seems likely that far better types than today’s are within reach. For example: 12 Frohne. D. and J.A. Pfänder. 1984. A Colour Atlas of Poisonous Plants. Wolfe Publishing Ltd., London 13 Chiej, R. 1984. Macdonald Encyclopedia of Medicinal Plants. Macdonald, London.
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Lost Crops of Africa: Fruits, Volume III Seedless forms have been created.14 These are small but nonetheless promising. They change the fruit from “a bag of seeds” to a glob of green jelly that is unique. Indeed, researchers in both France and Israel are growing the crop in winter under glass to produce seedless (i.e., parthenocarpic) fruit. Manipulating ploidy level (as done in watermelon, for instance) could be a means toward both improving flavor and inducing seedlessness. Improvement of taste may be achieved by combining genetic material from various sources.15 Spineless forms of the fruit are also known, and it seems probable that these, too, might prove useful. They could be a new foodstuff altogether—less of an oddity but easier to handle and something like a cucumber with a lime jelly interior. It is also possible to breed in other directions, toward more seed for example. Although the genetic potential is unknown, the disease-resistant and already seedy horned melon could become a premier crop for producing melon seed on a commercial scale. Also needed are better techniques to remove any fibrous seed coating and, as noted, confirming their edibility after processing (they are usually roasted, which detoxifies many seeds). Also as mentioned, emphasizing traits already useful in the fields of Africa should not be overlooked. These include types for pickling, or that have even longer storage lives, retain water reserves longer when left on the ground unpicked, or perhaps that even have greater spininess so their fruit with its precious liquid is saved for humans and not slurped down by foraging animals. Many believe its brightest future is as a new "cucumber.” Finally, its genetic potential as a leafy vegetable should also be explored. Indigenous Biodiversity It is highly important to create as wide as possible a collection of different genotypes from as much of Africa as possible to broaden the available genetic variability. It would seem logical that where this plant grows wild, explorers will find a wealth of genetic diversity.16 Remarkable diversity has been noted at the USDA Vegetable Laboratory, where some introductions are daylength sensitive, some show excellent resistance to nematodes, and there are varying degrees of spines on 14 Information from J.-Y. Peron. 15 “We found some lines with higher sugar and others with higher acidity, and crossed each of them with the commercial line,” wrote contributor Elaine Solowey. “From that, we got F1 lines with better taste and aroma.” 16 C.A. Schroeder wrote us, “There are, for example, many fine forms in Malawi.” However, another contributor reported that the useful diversity in Africa was limited. “Generally the variation in the species is surprisingly small. We scanned big areas to find some plants with different appearance and none was what we were after.”
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Lost Crops of Africa: Fruits, Volume III fruit from very large to none. It is important that variants be located, and useful types sorted, classified, and evaluated. Getting a better handle on the species’ diversity will lay the groundwork for all the developments to follow, and today much needs to be done to outline these genetic features. Horticultural Development Research to perfect cultivation practices is much needed. Some of this has already begun. In several countries research groups have been intensively studying the crop both under glass and in the open field. Production research needs include the artificial induction of fruit setting as well as optimizing growing conditions. Israeli researchers report getting reasonable yields of quality fruits with brackish irrigation (3.5-4.5 Ds/m), and many believe the salty water enhances the flavor. The plant’s interactions with nematodes, a curse of cucurbits, are certainly worth exploring. Its resistance could prove an important general finding, perhaps even giving this species a role in crop rotations—cleansing the soil of these very destructive soil nematodes. One group of researchers has also shown that using horned melon as rootstock for melon in root-knot infested soils can reduce galling, shoot-weight loss, and nematode levels at harvest.17 Techniques such as grafting can be important not just in high-value commercial horticulture, but also in the worst of situations where subsistence growers, for instance, have no choice what soils they use for planting their crops. Helping Other Melons By comparison with its better-known relatives, cucumber and melon, this crop shows exceptional resistance to diseases and pests. Thus, the possibility exists that horned melon could help broaden the gene pool of either or both. All three belong to the same genus, Cucumis. Genetically speaking, horned melon is closer to melon than cucumber, but so far no one has successfully crossed any of them.18 In attempts to transfer pest resistance to cucumber, researchers have found that fruits develop in crosses using horned melon pollen; however, no viable seeds from this chimera have yet been found to carry on these genes.19 Although gene transfer is undoubtedly difficult, all avenues seem worth pursuing because success would likely reduce costs for producing both crops and benefit the environment as well. In particular, it might dramatically boost the common melon’s resistance to nematodes, whitefly, and major diseases such as powdery mildew, downy mildew, and mosaic virus. 17 Sigüenza, C., M. Schochow, T. Turini, and A. Ploeg. 2005. Use of Cucumis metuliferus as a rootstock for melon to manage Meloidogyne incognita. Journal of Nematology 37(3):276–280. 18 Information from J.-Y. Peron and P. Nugent, who report that the pollen tube begins to germinate but does not reach the ovules. 19 Walters, S.A. and T.C. Wehner. 2002. Incompatibility in diploid and tetraploid crosses of Cucumis sativus and Cucumis metuliferus. Euphytica 128(3):371-374.
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Lost Crops of Africa: Fruits, Volume III SPECIES INFORMATION Botanical Name Cucumis metulifer E. Mey. ex Naudin Family Cucurbitaceae Synonyms Cucumis metulifer Naudin20 Common Names Afrikaans: rooikomkommer, rooi-agurkie, wilde-komkommer Bantu: nku, mutete, mugaika, mukaka, uhufafa Botswana: magabala, mogau English: spiny cucumber, horned cucumber, jelly melon, Kiwano© French: métulon, concombre africain German: Horn-Gurke, Hommelone Israel: Melano© Malawi: cucumber, bitter wild cucumber Shona: mutete, mugaika, mushonga, mugaka South Africa: bitter wild cucumber Tswana: magabala Venda: mukake Zambia: mugagachiga Zimbabwe: mushonga, mugaka, mutete, mugaika (S); ihalabujana; muGumudza’mbga (N) Zulu: uhufafa Description The plant is a sprawling, climbing, or trailing herbaceous annual that scrambles over bushes and trees in the wild. It has slender, hairy stems several meters long. The leaves are long-stalked and heart-shaped, shallowly 3 to 5 lobed, and dark green. Slender, curling, unbranched tendrils arise from the axils. The flowers are small, yellow, funnel-shaped, and opening to 5 lobes. The unisexual male and female flowers grow on the same plant. Seed can be true-to-type unless there is outcrossing. The female flower grows above a prickly green ovary, which enlarges to form the fruit. Honeybees are inefficient pollinators but its natural insect pollinators are unknown. The fruit is ellipsoid, about 6 × 12 cm, light green at first and ripening to bright orange. The skin usually has a broken pattern of light, scribbly reticulations, punctuated with pyramidal spines topped with a bristle. The “flesh” is translucent, green, and filled with whitish seeds. 20 This binomial, from 1859, is still the most-often cited scientific name (and should for now be used in internet searches). It has been “corrected” to the proper Latin termination under Article 32.7 of the Vienna 2006 International Code of Botanical Nomenclature.
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Lost Crops of Africa: Fruits, Volume III Distribution Although the botanical literature claims that this species can be found south of a line extending from Nigeria to Sudan and Ethiopia (and across to Yemen), the primary diversity is far south of that. The main concentrations are in Botswana, Zimbabwe (in mopane woodland), Malawi, Zambia, Mozambique, Namibia, Swaziland, and South Africa (lowveld and extending south along the coast to just touch the eastern edge of Cape Province). Commercial lines are exported from Kenya. Beyond Africa, the plant is currently under small-scale commercial cultivation at least in New Zealand, the United States, Israel, the Netherlands, Italy, Spain, Portugal, and France. It has also been introduced many other places. Environmental Requirements As a general rule, suitable sites for horned melon are those where cantaloupes can be cultivated (see Chapter 8, Melon). Daylength Flowering and fructification can be influenced by daylength. Flowering induction seems to require short days; days longer than 14 hours halt flowering. On the other hand, short days can lead to parthenocarpic fruits, in which the fruits grew directly from the ovule (like pineapples and bananas) without the intervention of pollination. Details are currently uncertain but the optimum length is said to be 12-hour days. Rainfall The plant is not particularly demanding of water and performs well with as little as 350 to 550 mm. However, dry air during the harvest period is a benefit. Altitude Although current commercial experience suggests that the plant performs best near sea level, it is probably better to say that it grows well at low to medium altitudes, up to perhaps 1,000 m. Near the equator, however, the upper limit may be closer to 1,800 m. Low Temperature The lower survival temperature is probably 0°C. However, cool temperatures during the growing period can suppress growth. A report from France notes that optimum germination temperatures were found to lie between 20 and 30°C. Germination was delayed at 12°C and totally inhibited at 8°C. High Temperature The plant’s growth is largely unaffected by temperatures as high as 40°C; however, it seems that temperatures over about 30°C affects flowering. In addition, germination is greatly inhibited at temperatures above 35°C.
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Lost Crops of Africa: Fruits, Volume III Soil This is a rugged plant in most soil types, and likely to survive in most African locations. However, top yields of quality fruits requires well-drained soils with organic matter and balanced nutrients. Related Species The genus Cucumis contains around 30 species of the Old World tropics, mostly Africa. It includes both cucumber (C. sativus) and melon (C. melo; see Chapter 8 in this section). Although cucurbits are notorious for hybridizing among themselves, attempts over the past 40 years to cross these species with horned melon have almost always been uniformly unsuccessful (see Next Steps, above). West Indian Burr Gherkin (Cucumis anguria L.)21 The burr gherkin has long been used for making fine pickles and is called by some the “true” gherkin (the word traditionally applies to immature cucumbers). Although native to Africa, this small fruit is commonly called “West Indian” gherkin because its cultivation and use is so widespread in those islands. It is also grown, and has also naturalized and sometimes spread as a pest, in other parts of the tropics. In Africa, wild types grow down from Tanzania and across to Namibia, and the cultivated West-Indian forms have been introduced in many places. The small fruits (about 5 cm long) are covered with burrs like horned melon, except the spines are fleshy. Though usually bitter, nonbitter types have been selected in several countries and, in addition to pickling, are eaten fresh, dried, and in soups. The leaves are also eaten. Both cultivars of the West Indian gherkin and the wild types of Africa have drawn the attention of scientists because of potential disease and pest resistance (especially whitefly), but little has been done to explore and improve the horticultural potential of these productive fruits. It is possible that its yield potential is higher than for pickling cucumbers.22 21 Also once called Cucumis longipes. 22 Information from Plant Resources for Tropical Africa, at www.prota.org.