DREISIGACKER S. ; KISHII M. ; LAGE J. ; WARHURTON M. ;

Bram Govaerts, Monica Mezzalama, Ken D. Sayre, Jose Crossa, Kelly Lichter, Veronique Troch, Katrien Vanherck, Pieter De Corte and Jozef Deckers

Dawit Alemu, Wilfred Mwangi, Mandefro Nigussie and David J.Spielman

Yam (Dioscorea spp., Dioscoreaceae) is the preferred alternative to cassava since the large, starchy tubers of cultivated species are usually free of toxic substances. Yam is a staple crop particularly in West Africa which provides over 90% of world production. However, due to the labor-intensive cultivation of the perennial herbaceous vines and its climatic requirements (humid tropics), yam production is less than 20% of cassava production.

Among the cereals the species of the genus Triticum belong to the most widely grown crops in the world. Common wheat (T. aestivum), durum wheat (T. durum) and Einkorn (T. monococcum) are the most important wheat species. Wheat can also be classified by growing season, i.e., winter wheat vs. spring wheat and by protein:starch content, i.e., hard wheat (high protein content) vs. soft wheat (high starch content). Intensive wheat production relies on applications of fertilizer, herbicides, fungicides and growth regulators timed with specific plant growth stages.

The seed of the tung tree (Vernicia fordii or Aleurites fordii, Euphorbiaceae) is the source of tung oil which is processed to an ingredient of paint and also motor oil. Trees are vegetatively reproduced by grafting scions of selected cultivars onto seedling rootstocks. Optimal climatic conditions for tung trees are subtropical with summer monsoons for providing a cool season to break dormancy and sufficient precipitation during the growing season.

Native to Australia, tea tree (Melaleuca alternifolia, Myrtaceae) is is a tree of the genus Melaleuca. For extracting the essential oil tea tree oil or melaleuca oil, the plant is, however, cultivated like a perennial herbaceous crop. Tea tree oil contains over 100 components, mostly monoterpenes, sesquiterpenes and their alcohols which is known for its antiseptic and antifungal effects.

Only distantly related to the potato and to the true yam, the sweet potato (Ipomoea batatas, Convolvulaceae) as the fifth most important food crop worldwide is a sub-/tropical herbaceous perennial vine which produces large, starchy, sweet tasting tuberous roots. These roots are long and tapered, with skin and flesh whose color ranges between brown and white. Besides for its roots, sweet potato is also cultivated for the leaves and young shoots of its aboveground herbaceous perennial vine.

Besides minor products including seed kernels as a snack, sunflower (Helianthus annuus, Asteraceae) has lost some of its importance as a major oil crop worldwide. It is predominantely cultivated for expressing oil for cooking and the food industry. The global distribution of the crop is limited due to its climatic requirements of short, hot summers with dry autumns during maturity and harvest.

Many of the important commercial species of sugarcane (Saccharum spp., Poaceae) belong to Saccharum officinarum. The perennial, up to 6 m tall C4 grass with sugar-rich, fibrous stalks is native to warm-temperate to tropical climates. It is the world's most important crop for sugar production, exceeding the production of sugarbeet at least six times. Increasingly important uses include the production of biofuel (ethanol) from its sugar and the production of heat and electricity from its bagasse after sugar extraction.