Environmental Engineering Reference
In-Depth Information
(Ceballos et al. 2006) and these have resulted in the recent discovery of amylose-free starch
mutant (Ceballos et al. 2007). Efforts are currently underway to introduce this gene into germ-
plasm adapted to the most important cassava growing environments. Compared with several
mutations reported for starches from other crops like maize and potato (
Solanum tuberosum
),
cassava offers very little variation because it is seldom self-pollinated yet most mutations are
recessive in nature.
The development of transgenic technologies in cassava could circumvent many of the problems
inherent in traditional improvement programs. By manipulating the embryonic culture systems of
cassava, four different techniques have been reported for recovering transgenic cassava plants with
integration of transgenes for desirable agronomic traits (Schöpke et al. 1996; Taylor et al. 2004).
These four transformation systems include production of somatic embryos from friable embryogenic
callus, cotyledon fragments, and immature leaf explants (Taylor et al. 2004). Recently, Ihemere et
al. (2006) succeeded in improving starch production in cassava by genetically modifying AGPase
activity using the bacterial AGPase gene,
glgC
. AGPase in plants plays a critical role in the regula-
tion of starch synthesis and is also involved in the rate-limiting step in starch synthesis.
Smith (2008) has recently reviewed prospects for increasing starch and sucrose yields for bioeth-
anol production in second-generation biofuel crops, under which cassava is classified. She recom-
mends the manipulation of starch degradation in organs in which starch turnover is occurring and
introduction of starch synthesis into the cytosol as possible options for increasing starch production
in the future.
13.5 commercIalIzatIon oF cassava as a BIoenerGy croP
Cassava has been promoted for introduction in most parts of Africa and Asia as a cash crop and
an alternative crop for food and industrial use. In Latin America, where the crop originates,
there is an increasing entrepreneurial entry into the cassava sector by small to medium growers
as well as investors (Hershey et al. 2004). In fact, cassava has been proposed as an ideal focus
for development-oriented research in Latin America (Hershey et al. 2004). Although cassava is
not yet competitive with sugarcane for bioethanol production in Brazil, there are indications that
bioethanol produced from cassava may be less expensive than that produced from sugarcane
(Energy and Energy Conservation News 2009). This is likely to shift producers' interest into
more investment in cassava. Production of cassava in Venezuela is also likely to increase after the
recent development of a biofuel production process by Venezuelan scientists (Global Bio-Energy
Industry News 2009). Currently, most of the cassava production in Latin America remains largely
for food production.
Several African countries are also promoting commercialization of cassava for food and alterna-
tive uses. Although the use of cassava for biofuel production in Africa is currently only exploited
in Nigeria, some African countries are reported to have biofuel research underway (Chege 2010).
There are signs of growing interest in using locally made cassava starch as an import substitute in
Uganda, Tanzania, Madagascar, and Malawi (Spotlight 2006). Evidence suggests that volumes of
traded cassava have been increasing about twice as fast as production in Zambia (Haggblade and
Nyembe 2008), probably as a result of erratic rainfall that has increasingly led to low maize yields
(Barratt et al. 2006). A task force has been initiated by the Zambia's Agricultural Consultative
Forum (ACF) to help accelerate commercial development of cassava and cassava-based products
(Haggblade and Nyembe 2008) such as bioenergy production. In West Africa, a renewed inter-
est in cassava as an alternative crop has been developed in the last decade (Camara et al. 2001).
Much more potential for use of cassava in Nigeria exists and is yet to be exploited (Kehinde 2006).
Although central Africa remains the biggest consumer of cassava in the continent, there has been
production decline in the region as a result of lack of resources to control biotic and abiotic stresses
(Aerni 2006). Availability of improved cassava cultivars adapted to the central African region is
likely to increase cassava production and commercialization.
