Cassava improvement: challenges and impacts

Abstract

Cassava (Manihot esculenta Crantz) is one of the two most important food crops in sub-Saharan Africa. This area accounts for most of the root harvest worldwide, followed by Asia and Latin America – the centre of origin for Manihot species. In Africa and Latin America, cassava is mostly used for human consumption, while in Asia and parts of Latin America it is also used commercially for the production of animal feed and starch-based products. Cassava is regarded as a crop adapted to drought-prone environments, where cereals and other crops do not thrive, and it also grows well in poor soil. There are about 100 wild Manihot species, which provide an important genetic endowment for cassava breeding. Professional cassava breeding started in the 20th century and was spurred on by increasing population demands. The main breeding goals are high yield per unit area, particularly in marginal or pest-prone environments. The most notable results from cassava breeding are seen today in sub-Saharan Africa, where it has been transformed from a poor man's crop to an urban food, and in Southeast Asia, where it has changed from a subsistence crop to an industrial cash crop. Long-term research by many international and national partners has led to breeding high-yielding cassava cultivars that increased crop yields up to 40%. Manipulation of genes from wild species has led to new cultivars that resist prevailing diseases and pests, allowing the avoidance of large-scale famine in sub-Saharan Africa. Cassava improvement continues to tap genetic variation through conventional breeding (including the use of wild species) and biotechnology, because many pathogens still take their toll and occasionally epidemics affect farmer fields significantly. However, new sources of variation are needed to genetically enhance the nutritional quality of this important food crop in Africa and other areas in the tropics of the developing world.

Wild Manihot species: botanical aspects, geographic distribution and economic value

“…Many of the species are lacticiferous, and some species such as M. glaziovii (Ceará rubber) are cultivated in Brazil and elsewhere for rubber production (Rogers, 1965;Rogers and Appan, 1973). This species was used by Storey and Nichols in the 1930s in former Tanganyka (today continental Tanzania) to transfer resistance to cassava mosaic disease (Nichols, 1947;Nassar and Ortiz, 2007). Many species such as those in section Tripartitae have their stems adapted to dry periods; dieback to a root crown regularly and shed their leaves during the dry season.…”

“…Produces obovate; basal lobes recurved polyploid types (Nassar, 2004a). Source of apomixis (Nassar, 2007;Nassar and Ortiz, 2007) M. pseudoglaziovii in calcium (Nassar, 1982) entire; all parts glabrous; leaves usually 5 lobed, rarely 3 lobed to soil toxicity (Nassar, 1985). (Nassar, 1978a(Nassar, , 1985 shallowly stellate (Nassar, 1982).…”

“…It is cultivated between 30° N and 30° S of the equator, in areas where the mean annual temperature is greater than 18°C (Nassar and Ortiz, 2007). This tuberous root crop ranks among the two most important staples of sub-Saharan Africa.…”

“…It also grows well in poor soil. Jennings and Iglesias (2002) provide an overview of the state of the art of cassava breeding as well as remaining challenges, whereas Nassar (2004b) and Nassar and Ortiz (2007) assess the impacts on cassava breeding programs worldwide. Although significant gains are reported in Africa (Dixon et al, 2003), there are pests and other constraints affecting crop yield.…”

Desenvolvimento vegetativo e associação micorrízica em plantas de mandioca adubadas com resíduo agroindustrial

“…planta da família Euphorbiaceae, é utilizada na alimentação humana e animal (BURGOS et al, 2010), devido à composição químico-bromatológica, que apresenta 26,2 % de proteína bruta, 37,9 % de fibra em detergente neutro e 43 % de digestibilidade in vitro da matéria seca da parte aérea (FERREIRA et al, 2009). Além disso, esta espécie pode ser cultivada em solos ácidos e com baixa fertilidade natural (NASSAR; ORTIZ, 2006). Ressalta-se ainda que, plantas de mandioca apresentam resistência a períodos de estiagem e capacidade de utilização eficiente da água do solo, o que possibilita o seu cultivo em regiões de secas prolongadas .…”