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Dika
Dika grows in african tropical lowlands and steamy zones, which are difficult to farm with modern agronomic approaches and is appreciated for its various uses by the population to which the products assure a critical income. Dika lends itself to fight malnutrition in the west of Africa, because it contains a lot of energy and 6 of 8 essential amino acids. The genus name commemorates E.G. Irving 1816-1855 a Scottish botanist.

Geographic distribution
Irvingia gabonensis is indigenous to the humid forest zone from the northern tip of Angola, including Congo, DR Congo, Nigeria, Côte d'Ivoire and south-western Uganda.

It is planted in parts of this area, e.g. in south-western Nigeria and southern Cameroon, and also in Côte d’Ivoire, Ghana, Togo and Benin.

Biophysical limits
The tree is present in the tropical wet and dry climate zone. Dika grows naturally in canopied jungle, gallery forests and semi-deciduous forests. It grows at altitudes from 200-500 m with annual rainfalls from 1200-1500 mm. Supported temperature ranges from 20° to 38° C under slightly shaded to very bright, clear skies. Deep soils with more than 150 cm are requested with a moderate fertility and good drainage. pH can vary from 4.5 to 7.5.

Appearance
Irvingia gabonensis grows straight, up to a height of 40 m and 1 m in diameter. It has buttresses till a hight of 3 m. The outer bark is smooth to scaly with grey to yellow-grey color. The crown is evergreen, spherical and dense. Leaves are elliptic, one margin is often a little rounder than the other, acuminate, dark green and glossy on the upside. Flowers are yellow to greenish-white in small panicles. The flowers are bisexual. The fruit is nearly spherical, green when ripe with a bright orange pulp. The stone is woody and contains one seed. Seedling germinate epigeally.

Reproduction
Irvingia gabonensis is pollinated by Coleoptera, Diptera, Hymenoptera and Lepidoptera. It flowers from March to June and has two fruiting seasons: from April to July and from September to October. Seeds are dispersed by specialized vertebrates as elephants and gorillas. By reducing the number of those animals, the spread and regeneration of dika decreases and it becomes dependent on human planting.

Products
The fruits can be eaten freshly, that is why the name African mango is used for dika. The fruits are processed into jelly, jam, juice and sometimes even wine. The pulp has also been used to prepare black dye for cloth coloration. Compared to the seed the fruit is only a tiny resource. The episperm of the fruit has to be cracked open to get to the seed. Seeds, also called dika nut, are eaten raw or roasted. Mostly however they are pounded to butter or a chocolate like block. Seeds can be pressed to produce an edible oil (solid at ambient temperatures) or margarine which are used for cooking. The oil can also be processed further to soap, cosmetics or pharmaceuticals. The press cake can be used as cattle feed or as thickening agent for soup. Seeds can be ground or crushed and used as thickening and flavoring agent in soups and stews. This food-thickening property is thought to be caused by mucilaginous polysaccharides, which become more viscous with cooking and is called "drawability". They can also be made into a cake called „dika bread“ for preservation. For various medicinal use mostly bark and leaves are utilized. It is employed as a purgative, for gastrointestinal and liver conditions, for hernias and urethral discharge or to sores and wounds. The wood is very hard and therefore usually used for heavy construction work as making ship decks or railway ties. Dead branches are used as firewood. The trees are used in agroforestry systems to shade other crops, especially cocoa and coffe. They are also used to reduce erosion. Cities start using it to shade streets, as shelter belts of for beautification. Thousands of tons of Dika seeds are traded each year. This happens mostly within Africa, but export to the USA starts. As a cash crop Dika produces income.

Nutritional aspects of Irvingia gabonensis
Nutritive value of the kernels per 100 g edible portion, which corresponds to about 2918 kJ of energy:

Besides the mentioned components kernels of Irvingia gabonensis contain traces of thiamine, riboflavin and niacin. The approximate fatty acid composition is myristic acid 33-70%, laureic acid 20-59%, oleic acid 1-11%, palmitic acid 2% and stearic acid 1%. The contained amino acids are reasonably balanced for human nutrition. Since lysine, tryptophan, valine, threonine, isoleucine and phenylalanine have high concentrations in the seed, first limiting amino acids are methionine and [[ccysteine].

Unlike the pulp of some other Irvingia spp. the pulp of the fruit of Irvingia gabonensis is juicy and sweet and is eaten freshly. Nutritive value per 100g edible portion of fruit pulp, which corresponds to 255 kJ of energy: energy: The fruit pulps main flavor components are zingiberene and α-curcumene, ethyl and methyl esters of cinnamic acid, dodecanal and dodecanol. This results in spicy-earthy, fruity, wine-yeast flavor notes.

Management
Till some years ago 90% of the dika products were harvested from scattered, wild trees. They were not especially planted, because it was believed, that it takes up to 15 years till a tree bears fruits. Although they were not planted, their occurrence is high because they were also rarely lumbered. In a plantation using marcots (air-layering plants) florisation was observed two to four years after planting. Dika has no history as managed crop, that is why not a lot experience is gathered upon cultivating it. Germination from seeds is low and when they are not handled carefully, most fail to germinate. In trials was observed that they already three to five years after planting. Harvesting fruits at the mature green stage and let maturate at 26°-29° C were preferred in color and texture to those which naturally ripened on the tree. The seeds are mostly extracted by braking the episperm by hand. Different techniques are common in different countries. Sometimes seeds are harvested from fresh fruits, sometimes they are let fermenting in the sun. All those techniques are very time consuming.

Breeding
The domestication of Dika is in it's early years. Around 1990 vegetative propagation started allowing mass replication and selection. Grafting, budding air-layering, marcotting and cuttings are feasible when they are applied on young wood.

Future developments
A elite germplasm bank should be built up. This germplam could than be used for vegetative propagation to improve the farmers welfare with improved plant material. Farmers could also be supported in cultivation. Future breeding aims are: multiple bearing - carrying fruits several times a year, precocity - fruiting at younger age, split fruits - nuts which release the seed by themselves and good form - dwarfing is especially valued, because it simplifies harvest. Invention of a nut-cracking device would help the further dispersion of the tree. A selection for "drawability", which could be used by food technology seems probable.