Principles of Plant Genetics and Breeding

Figure 1 Farmer (left) and researcher (center) admiring a bag
of quality protein maize being offered for sale in a store in
Ghana, West Africa.
References
Improving protein content
by genetic engineering
Nutritional quality augmentation through the addition
of new quality traits, removing or reducing undesirable
traits, or other manipulations, is an important goal in the
bioengineering of food crops. Crops that feed the world
are primarily cereals, roots and tubers, and legumes.
Unfortunately, they are nutritionally inadequate in providing
certain amino acids required for proper growth
and development of humans and monogastric animals.
For example, cereals are generally deficient in lysine and
BREEDING COMPOSITIONAL TRAITS AND ADDED VALUE 409
extension (Figure 1). To date, QPM varieties have been
released in about 15 sub-Saharan African countries.
Current efforts led by CIMMYT and IITA seek to incorporate
QPM into elite and local cultivars through a
process of conversion of NM germplasm to QPM.
Conversion involves the use of backcrossing of normal
maize to QPM using donor QPM populations or
inbred lines. After one or two backcrosses, the plants
are selfed or sib-pollinated, and segregating opaque-2
phenotype grains, which appear partly opaque on
light tables, are selected for further backcrossing. Two
to three backcrosses are often enough to recover the
recurrent parent genotype and phenotype in addition
to the modified opaque-2 grain character. However, in
some cases, additional cycles of improvement may be
required to accumulate enough modifier genes to
recover the normal maize endosperm phenotype.
Marker-assisted selection has been employed to speed
up the backcrossing. In this procedure, a DNA marker
that is very closely linked to the opaque-2 gene is
used – as a replacement of the phenotypic test – to
select progeny carrying the desired allele based on the
analysis of leaf samples from young plants.
Ahenkora, K., S. Twumasi-Afriyie, W. Haag, and B.D. Dzah. 1995. Ghanaian kenkey from normal maize and quality protein
maize: Comparative chemical composition and rat growth trials. Cereals Communic. 23:299–304.
Mertz E.T., L.S. Bates, and O.E. Nelson. 1964. Mutant genes that changes protein composition and increases lysine content
of maize endosperm. Science 145:279–280.
National Research Council. 1988. Quality-protein maize. Academy Press, Washington, DC.
Okai, D.B., S.A. Osei, A.K. Tua, et al. 1994. The usefulness of Obatanpa, a quality protein maize variety in the feeding of
pigs in Ghana. Proc. Ghana Anim. Sci. Symp. 22:37–43.
Osei, S.A., C.C. Atuahene, A. Donkoh, et al. 1994. Further studies on the use of quality protein maize as a feed ingredient
for broiler chickens. Proc. Ghana Anim. Sci. Symp. 22:51–55.
Twumasi-Afriyie S., B.D. Dzah, and K. Ahenkora. 1996. Why QPM moved in Ghana. In: Maize productivity gains through
research and productivity dissemination (Ransom, J.K., B.T. Palmer, Z.O. Mduruma, S.R. Waddington, K.V. Pixley, and
D.C. Jewel, eds), pp. 28–31. Proceedings of the Fifth Eastern and Southern Africa Maize Conference, Arusha, Tanzania.
CIMMYT, Mexico.
Vasal, S.K., G. Srivisan, S. Pandey, F. Gonzalez, J. Crossa, and D.L. Beck. 1993. Heterosis and combining ability of
CIMMYT’s protein maize germplasm: Lowland tropical. Crop Sci. 33:46–51.
threonine, whereas legumes are generally deficient in
sulfur amino acids. In some species (e.g., rice) in which
the amino acid balance is relatively appropriate, the
overall protein quantities are low.
Molecular genetic approaches are being adopted for
genetically engineering seed protein. They may be categorized
as:
1 Altering the amino acid profile of the seed.
2 Selective enhancement of expression of existing genes.
3 Designing and producing biomolecules for nutritional
quality.