CHAPTER ONE
1.1 INTRODUCTION
Sweet potato (Ipomoea batatas (L) Lam.), belongs to the family Convolvulaceae and
originated from South America from where it was introduced to Europe between 1565 and 1573
(Adams, 2005). It is a hexaploid, and usually considered the only species of Ipomoea of
economic importance. Horton and Sawyer (1985) as cited by Babatunde et al., (2007) reported
that globally, sweet potato is a very important food crop after rice, wheat and corn. Also, of the
world’s root and tuber crops, sweet potato ranks third after Irish potato and cassava (Ikeorgu,
2003). It is the only crop among the root tuber crops that had a positive per capita annual rate of
increase in production in sub-Saharan Africa FAOSTAT, (2007). Sweet potato has a high yield
potential that may be realized within a relatively short growing season and it can adapt to a wide
range of ecological conditions ranging from 0.2000-0.4000 meters above the sea level and can
grow in areas between 30N and 30S of the equator (Hahn and Hozyo, 1984) as cited in Belehu,
(2003). Sweet potato has become an important staple food in the East African region, after
banana and maize (FAO, 1991). Small-scale farmers produce it under traditional farming
systems where it serves as food to humans and livestock and for industrial use, but generally,
yields vary with cultivar, disease resistance, location and production practices (Onwueme, 1978).
The importance of sweet potato is increasing in Nigeria’s farming and food systems
because it is easy to plant, matures quickly and has enormous industrial and economic potentials
(Chukwu, 1999). It is equally a crop with huge promise for food security in developing countries.
Also it has high nutritional energy qualities, and the leaves are consumed as vegetables
(Holloway, 1993; Chukwu, 1999). In Kwara State of Nigeria, particularly in Offa Local
Government Area (LGA), sweet potato has enjoyed some traditional sentiments of the people
resulting to the harvest season being celebrated with feasting and cultural dances (Agbo and Ene,
16
1993).
Despite the unlimited promises that this staple crop has, its production has been
insufficient in Nigeria and there is need to improve on it through increased efficiency (Ndukwu,
2010). This insufficiency could be enhanced by proper education of farmers on the use of
developed techniques and adequate use of materials in response to better information (Idiong,
17
2006). With the difficulties encountered in developing countries in adopting improved
technologies due to resource poverty, efficiency has become a very significant challenge in
increasing productivity and therefore requires concerted effort across disciplines to improve on
this existing menace (Ali and Chandry, 1990).
Though Nigeria with an estimated production quota of 3.49 million metric tons ranks first
in Africa, followed by Uganda her contribution to global sweet potato production is only about
0.2 percent despite her wide arable land and favorable environmental conditions (FAO 2007).
This low global potato output by Nigeria could be as a result of poor breeding programs,
varieties and farming systems employed during farming and inconsistencies in performance of
varieties over locations. There is therefore no gain-saying that it is necessary to evolve varieties
with high yield potentials and consistent performances over diverse environments, because
productivity of a variety is the function of its adaptability while the adaptability is dependent on
fitness (stability) and flexibility. Evolution of more high yielding and stable varieties will as a
matter of fact give us a global standing in production and utilization of sweet potato.
To further buttress the foregoing issues, it has been demonstrated that micronutrient
enrichment traits are available within genomes of the major staple food crops, including sweet
potato. Research to identify accessions high in different nutritional qualities (dry matter, protein,
starch, sucrose, ß-carotene, Fe, Zn, Ca and Mg) has been initiated by Center for International
Potato (CIP), for germplasm in genebank and breeding which is evident in Suda et al., (2003).
Such characterization needs to be done for the germplasm from the Nigerian region. Sweet
potato in relation to other vegetables has nutritional potentials with endowed medicinal
properties for healthy living, like antioxidant activities. Antioxidants are substances or nutrients
present in our food which can increase cellular defense and help prevent oxidative damage to
cellular component of our bodies in the hope of maintaining health and preventing diseases such
as cancer and coronary heart disease (Mervat and Hanan, 2009). In addition to many other uses
in medicine and industrial field, it is used in manufacturing cosmetics and food preservation and
colorant. Namiki (1990) cited by Mervat and Hanan (2009) reported that the synthetic
antioxidants have restricted use in food, as they are suspected to be carcinogenic. The importance
of searching for and exploiting natural antioxidants has increased greatly in recent years Patil et
al. (2009). While, antioxidant is a class of plant secondary metabolites, the plant kingdom offers
vast array of valuable natural polyphenolic compounds, several isolated plant constituents as
well as crude extracts of vegetables and fruits; which have been recognized to possess beneficial
effects against free radicals in biological systems as antioxidants (Yi Fang and Xianzona, 2002).
National Root Crops Research Institute (NRCRI) Umudike and the International Institute
for Tropical Agriculture (IITA) Ibadan have made a great effort to evolve new varieties that will
meet the commercial, subsistence and nutritional needs of the nation. Unfortunately, these
varieties have not received a wide evaluation to ascertain their yield potentials and agromorphological
characteristics across diverse environmental conditions. To this effect, Nwankwo
et al. (2010) stated that morpho-agronomic characterization provides information that could be
of immense support to a plant breeder and other users in the efficient use of newly acquired
materials. They equally opined that an unevaluated and uncharacterized accession in a
germplasm is a resource lying waste; emphasizing the need for the breeder to evaluate and
characterize his new collections to ascertain their breeding worth. Gruneberg et al. (2005)
maintained that the identified and characterized accessions could be promoted as superior
varieties to farmers or used as parents in a comprehensive breeding program for improved
nutrition in sweet potato varieties without negatively impacting crop yields.
1.1 INTRODUCTION
Sweet potato (Ipomoea batatas (L) Lam.), belongs to the family Convolvulaceae and
originated from South America from where it was introduced to Europe between 1565 and 1573
(Adams, 2005). It is a hexaploid, and usually considered the only species of Ipomoea of
economic importance. Horton and Sawyer (1985) as cited by Babatunde et al., (2007) reported
that globally, sweet potato is a very important food crop after rice, wheat and corn. Also, of the
world’s root and tuber crops, sweet potato ranks third after Irish potato and cassava (Ikeorgu,
2003). It is the only crop among the root tuber crops that had a positive per capita annual rate of
increase in production in sub-Saharan Africa FAOSTAT, (2007). Sweet potato has a high yield
potential that may be realized within a relatively short growing season and it can adapt to a wide
range of ecological conditions ranging from 0.2000-0.4000 meters above the sea level and can
grow in areas between 30N and 30S of the equator (Hahn and Hozyo, 1984) as cited in Belehu,
(2003). Sweet potato has become an important staple food in the East African region, after
banana and maize (FAO, 1991). Small-scale farmers produce it under traditional farming
systems where it serves as food to humans and livestock and for industrial use, but generally,
yields vary with cultivar, disease resistance, location and production practices (Onwueme, 1978).
The importance of sweet potato is increasing in Nigeria’s farming and food systems
because it is easy to plant, matures quickly and has enormous industrial and economic potentials
(Chukwu, 1999). It is equally a crop with huge promise for food security in developing countries.
Also it has high nutritional energy qualities, and the leaves are consumed as vegetables
(Holloway, 1993; Chukwu, 1999). In Kwara State of Nigeria, particularly in Offa Local
Government Area (LGA), sweet potato has enjoyed some traditional sentiments of the people
resulting to the harvest season being celebrated with feasting and cultural dances (Agbo and Ene,
16
1993).
Despite the unlimited promises that this staple crop has, its production has been
insufficient in Nigeria and there is need to improve on it through increased efficiency (Ndukwu,
2010). This insufficiency could be enhanced by proper education of farmers on the use of
developed techniques and adequate use of materials in response to better information (Idiong,
17
2006). With the difficulties encountered in developing countries in adopting improved
technologies due to resource poverty, efficiency has become a very significant challenge in
increasing productivity and therefore requires concerted effort across disciplines to improve on
this existing menace (Ali and Chandry, 1990).
Though Nigeria with an estimated production quota of 3.49 million metric tons ranks first
in Africa, followed by Uganda her contribution to global sweet potato production is only about
0.2 percent despite her wide arable land and favorable environmental conditions (FAO 2007).
This low global potato output by Nigeria could be as a result of poor breeding programs,
varieties and farming systems employed during farming and inconsistencies in performance of
varieties over locations. There is therefore no gain-saying that it is necessary to evolve varieties
with high yield potentials and consistent performances over diverse environments, because
productivity of a variety is the function of its adaptability while the adaptability is dependent on
fitness (stability) and flexibility. Evolution of more high yielding and stable varieties will as a
matter of fact give us a global standing in production and utilization of sweet potato.
To further buttress the foregoing issues, it has been demonstrated that micronutrient
enrichment traits are available within genomes of the major staple food crops, including sweet
potato. Research to identify accessions high in different nutritional qualities (dry matter, protein,
starch, sucrose, ß-carotene, Fe, Zn, Ca and Mg) has been initiated by Center for International
Potato (CIP), for germplasm in genebank and breeding which is evident in Suda et al., (2003).
Such characterization needs to be done for the germplasm from the Nigerian region. Sweet
potato in relation to other vegetables has nutritional potentials with endowed medicinal
properties for healthy living, like antioxidant activities. Antioxidants are substances or nutrients
present in our food which can increase cellular defense and help prevent oxidative damage to
cellular component of our bodies in the hope of maintaining health and preventing diseases such
as cancer and coronary heart disease (Mervat and Hanan, 2009). In addition to many other uses
in medicine and industrial field, it is used in manufacturing cosmetics and food preservation and
colorant. Namiki (1990) cited by Mervat and Hanan (2009) reported that the synthetic
antioxidants have restricted use in food, as they are suspected to be carcinogenic. The importance
of searching for and exploiting natural antioxidants has increased greatly in recent years Patil et
al. (2009). While, antioxidant is a class of plant secondary metabolites, the plant kingdom offers
vast array of valuable natural polyphenolic compounds, several isolated plant constituents as
well as crude extracts of vegetables and fruits; which have been recognized to possess beneficial
effects against free radicals in biological systems as antioxidants (Yi Fang and Xianzona, 2002).
National Root Crops Research Institute (NRCRI) Umudike and the International Institute
for Tropical Agriculture (IITA) Ibadan have made a great effort to evolve new varieties that will
meet the commercial, subsistence and nutritional needs of the nation. Unfortunately, these
varieties have not received a wide evaluation to ascertain their yield potentials and agromorphological
characteristics across diverse environmental conditions. To this effect, Nwankwo
et al. (2010) stated that morpho-agronomic characterization provides information that could be
of immense support to a plant breeder and other users in the efficient use of newly acquired
materials. They equally opined that an unevaluated and uncharacterized accession in a
germplasm is a resource lying waste; emphasizing the need for the breeder to evaluate and
characterize his new collections to ascertain their breeding worth. Gruneberg et al. (2005)
maintained that the identified and characterized accessions could be promoted as superior
varieties to farmers or used as parents in a comprehensive breeding program for improved
nutrition in sweet potato varieties without negatively impacting crop yields.
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