Cassava Origin: A briefly Introduction for Breeding

Luis B. Gómez L.

Cassava –Manihot esculenta Crantz (also named Yuca, Mandioca, Manioc, Mushu) is an annual crops from the botany family Euphorbiaceae, cultivated in tropical and subtropical regions for it starchy tuberous root, source of carbohydrates. In many African countries, cassava leaves are preferred like vegetable rich in proteins. Furthermore, cassava is used for animal feed. Normally, Cassava is consumed just boiled, however exist different processing such as to make cassava bread (casabe), design metallic plates, flour, biodegradable plastic, gum, use of cassava glucose syrup in confectionery, pharmaceutical and food industries . Also, researchers have begun to evaluate the use of cassava as an ethanol bio-fuel fee-stock. On average it is estimated than one ton of cassava root produce around 166 liters of ethanol.

Cassava plays importance role for developing countries because it does well on poor soils, with low rainfall, adverse climatic conditions limits and can survive underground for long time, then can be harvested as required. For those reasons, cassava is considerate as a good crop for food safety. Cassava is ranked as the fourth most important crop after wheat, rice and maize and the third largest source for food of carbohydrates in the world, also is the staple food for more than 800 million people in the world. According to FAO statistic, in 2008, production of cassava was 230 tons millions. Cassava production is mainly in Africa, Asia and Latin America and Caribbean with 54.2%, 29.4% and 18.3% respectively. Five countries produce 70% of the world production: Nigeria, Brazil, Thailand, Indonesia and Democratic Republic of Congo. The largest exporter country is Thailand with 87.5% of the world exportations in 2001 and the largest importer country is China with 34.9% in 2001 of the world importations.

Most important breeding objectives

Objectives for cassava breeding vary from one to another country and depend on its final use such as industrial uses, animal feed, human consumption and subsistence. However, the most important objectives at cassava breeding programs nowadays are: a) yield potential ( starch production, very important for industrialization) , b) yield stability (is necessary to guarantee food security in many countries where cassava is the main subsistence crop; normally is associated with resistance/tolerance to biotic and abiotic stresses) , c) pest and disease resistance (cassava mosaic disease – CMD-, cassava brown streak disease – CBSD-, frogskin disease, bacterial blight induced by Xanthomonas axonopodis pv. manihotis, Super elongation disease are the most important disease in cassava. Green mite - Mononychellus tanajoa -, mealybugs – Phenacoccus manihotis -, Thrips –Frankliniella williamsi and Scyrtotrisps manihoti -, whiteflies – Bemisia tabaci, Aleurotrachelus socialis- are important pests considerate in programs breeding), and, d) root quality (includes carotene content, root storability for reduce post harvest deterioration, cooking quality, normally associated with morphological traits such as roots peel colors and leaf petiole or the shoot, cyanogenic potential in roots, bulking capacity and higher protein content in root) .

Lebot, 2009, describes the following ideotype for cassava: only one stem per cutting, high ratio roots/stems, leaf area index between 3-3.5, large single leaf area, short internodes and height of plant less than 2 m, leaves of long life, eight tuberous roots approximately, roots short, compact, easy to harvest and to peel, quality traits (starch, protein, carotene, low cyanogenic glucosides) and reduced post harvest deterioration.

Chromosome composition

Genus wild species of Manihot are considerate as a normal diploids on regular meiosis and have a chromosome number of 2n=36. However, in Vanuatu, farmers have selected and cultivated natural triploids plants. Also, allopolyploid have been reported, allo-tetraploid, with basic chromosome number of x=9.

Current popular cultivars

There are more than 20, 000 accessions of cassava and its relatives preserved in ex situ germplasm in collection in Centro Internacional de Agricultura Tropical (CIAT, Colombia), International Institute of Tropical Agriculture (IITA, Nigeria) and national programs of more than 45 different countries in the world. Golden Yellow, Katabang and Alakan (Philippines), Oloronto, Oyarugba dudu and Eye dudu (Nigeria), Mocana, Valencia and Dame más (Dominican Republic), Sabanera, Costeña (Mexico), Bibiana, Tiangua and Embrapa 8 (Brazil), Rayong 60, Sriracha 1 and Kasetsart 50 (Tailand) are recognized cassava cultivars nowadays.

Origin of the specie

The exact place and circumstance of origin of cassava is under discussion yet, although it has been debated profusely. Many authors recognized that Brazil is the origin center, where there are the most amount of wild species of Manihot (around 80 species), but there isn’t enough archeological evidence to confirm Brazilian domestication of Cassava. Other possible center is Central America and the Caribbean where are host approximately 17 Manihot species and, in Mexico it was found cassava leaves that are from 2500 years ago, and cassava starch in human coprolites (2100-800 years old). Also, other places in South America could be possible; where there are graphical representations of root dated 2000 BC (dry coastal savannahs of Venezuela and Peru) and ovens to cook casaba dated 1200 BC in Colombia. However is considered a mystery certain origin center of Cassava, there isn’t doubt that it’s from Americans, especially from South America, Caribbean and Central America.

Allen, 2002, confirm that the wild parents of cultivated cassava (Manihot esculenta ssp. esculenta) are M. esculenta ssp. flabellifolia and M. esculenta ssp. peruviana and that the closest wild related specie is M. pruinosa. Other wild related specie of Manihor esculenta Crantz are: M. carthaginensis, M. aesculifolia, M. graham and M. saxicola, M. pohlii, M. zehntneri , M. glaziovii, M. peudoglaziovii, M. aescullifolia, M. pilosa, M. dichotoma, M. neusana and M. anomala.

Breeding Perspectives

Future considerations in cassava breeding are focus on improve complex traits such as higher yield and dry matter content in the roots, early bulking, high starch content and low HCN (Hydrocyanic acid). Also, an important trait is the resistance to abiotic stress.

The amount (around 100) of available wild Cassava related species represents a opportunity for Cassava Breeding. Also, International Institutes such as CIAT, IITA, Embrapa (Brazil), national research centers in China, Cuba, India, Indonesia, Thailand, Dominican Republic, Vietnam and others, have genetics material collected available for breeding.

References

1. Allem, A. (1994). The Origin of Manihot esculenta Crantz (Euphorbiaceae). Genetic Resources and Crop Evolution 41(3):133-150.
2. Allem, A. (1999). The Closest wild relatives of cassava (Manihot esculenta Crantz). Euphytica 107(2):123-133.
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13. Montaldo, Alvaro (1985). “La Yuca o Mandioca”. Editorial IICa: Costa Rica.
14. Wikipedia (2010). “Cassava”. http://en.wikipedia.org/wiki/Cassava

(Image: Franz Eugen Köhler, 1987. Obtained from http://es.wikipedia.org/wiki/Archivo:Koeh-090.jpg)