**6. Breading efforts in QPM**

Although QPM breeding has been practiced for more than 60 years, genetic mechanism and genetic components controlling endosperm modification are not clearly understood. Opaque-2 (o2) modifier loci have been distributed on six chromosomes [26]. The opaque-2 modification is positively correlated with 27-kDa γ-zein in an F2 population and recombinant inbred lines (RILs), which are produced through crosses between QPM and an o2 mutant as parents [42]. Gene silencing

**37**

crosses [54, 55].

*DOI: http://dx.doi.org/10.5772/intechopen.89038*

also affects the maize production [51].

*Quality Protein Maize: An Alternative Food to Mitigate Protein Deficiency in Developing…*

or deletion of γ-zeins eliminates 27-kDa γ-zein expression, and it eliminates the formation of vitreous endosperm [43]. Zein proteins are stored at rough endoplasmic reticulum-retained protein bodies in the endosperm [44]. For protein body formation, 27-kDa γ-zein, 16-kDa γ-zein and 15-kDa β-zein plays an important role in initiation and stabilization [19]. Zein gene knockout studies in QPM showed irregular, clumped protein bodies in lesser number and an opaque phenotype [29]. Worldwide different agricultural research centers are showing significant progress in increasing the lysine and tryptophan content in the whole grain [16]. Maize varieties' improvement and QPM conversion programs, a multi-trait selection procedure using independent selection levels has been employed to increase grain yield, resistance to pest and diseases, accumulate modifiers and improve other important traits in which QPM germplasm is defective [4]. In QPM breeding program, protein and tryptophan analysis in germplasm is an important step [45, 46]. A broad range of the CIMMYT's maize populations have been converted to QPM. This germplasm is reported to have high potential for QPM cultivar development [47, 48]. QPM with high protein quality and grain yield could be accepted by the farmers [1]. QPM germplasm has been widely used for the development of QPM cultivars with high grain yield in African countries [16]. The important problem in QPM breeding is abiotic stresses. Water stress and soil infertility are the most important stresses that reduce maize productivity in developing countries. It affects major maize yield loss in African countries [49]. High land usage affects the soil fertility and decreases the nitrogen content in the soils [50]. Global climate change could influence the soil fertility and water holding capacity, and it

Worldwide, a large number of normal maize hybrids have been released and commercialized. But the QPM-based germplasm is quite narrow, and significantly small numbers of genetically diverse QPM hybrids are available. Nearly 12 QPM hybrids have been released in India, compared to greater than hundred normal maize hybrids [52]. In this context, it is necessary to develop various QPM varieties across the world. Conversion of QPM through conventional breeding takes at least 10–15 years. Conversion of elite normal maize hybrids into QPM hybrids requires lesser time, initially due to tested combining ability, heterosis and adaptability of the released hybrids [53]. Opaque-2 recessive allele introgression through conventional backcross breeding of 6–7 generations is required. Through marker-assisted advanced backcross breeding, time could be significantly reduced to two back-

The opaque-2 mutation in maize inspired the research interest, with wishes to significantly increase the nutritional status of maize consumers in developing countries. QPM, which has high lysine and tryptophan, holds the security of improving the nutritional condition of children whose main staple food is maize. It is an alternative food for protein supplement in the diet. QPM has been an alterna-

Under stress conditions, the quality of the QPM protein does not vary, but the modifications of endosperm and the content of the proteins vary greatly. To enhance the yield of QPMS under different stress conditions is the major constrain for the breeders. Drought stress affects on QPM yield mainly in grain-filling stage [56]. Some studies reported that the supply of selenium to the plant could reduce the negative effects of the water stress conditions and is considered as the cost-efficient approach to improve the quality and yield of maize [57]. Supplying nitrogen and sulfur results in the enhanced growth and yield of QPMs [58]. Some

tive to the people who are using synthetic lysine and tryptophan.

**6.1 QPM genotypes for stress conditions**

#### *DOI: http://dx.doi.org/10.5772/intechopen.89038 Quality Protein Maize: An Alternative Food to Mitigate Protein Deficiency in Developing…*

or deletion of γ-zeins eliminates 27-kDa γ-zein expression, and it eliminates the formation of vitreous endosperm [43]. Zein proteins are stored at rough endoplasmic reticulum-retained protein bodies in the endosperm [44]. For protein body formation, 27-kDa γ-zein, 16-kDa γ-zein and 15-kDa β-zein plays an important role in initiation and stabilization [19]. Zein gene knockout studies in QPM showed irregular, clumped protein bodies in lesser number and an opaque phenotype [29].

Worldwide different agricultural research centers are showing significant progress in increasing the lysine and tryptophan content in the whole grain [16]. Maize varieties' improvement and QPM conversion programs, a multi-trait selection procedure using independent selection levels has been employed to increase grain yield, resistance to pest and diseases, accumulate modifiers and improve other important traits in which QPM germplasm is defective [4]. In QPM breeding program, protein and tryptophan analysis in germplasm is an important step [45, 46]. A broad range of the CIMMYT's maize populations have been converted to QPM. This germplasm is reported to have high potential for QPM cultivar development [47, 48]. QPM with high protein quality and grain yield could be accepted by the farmers [1]. QPM germplasm has been widely used for the development of QPM cultivars with high grain yield in African countries [16]. The important problem in QPM breeding is abiotic stresses. Water stress and soil infertility are the most important stresses that reduce maize productivity in developing countries. It affects major maize yield loss in African countries [49]. High land usage affects the soil fertility and decreases the nitrogen content in the soils [50]. Global climate change could influence the soil fertility and water holding capacity, and it also affects the maize production [51].

Worldwide, a large number of normal maize hybrids have been released and commercialized. But the QPM-based germplasm is quite narrow, and significantly small numbers of genetically diverse QPM hybrids are available. Nearly 12 QPM hybrids have been released in India, compared to greater than hundred normal maize hybrids [52]. In this context, it is necessary to develop various QPM varieties across the world. Conversion of QPM through conventional breeding takes at least 10–15 years. Conversion of elite normal maize hybrids into QPM hybrids requires lesser time, initially due to tested combining ability, heterosis and adaptability of the released hybrids [53]. Opaque-2 recessive allele introgression through conventional backcross breeding of 6–7 generations is required. Through marker-assisted advanced backcross breeding, time could be significantly reduced to two backcrosses [54, 55].

The opaque-2 mutation in maize inspired the research interest, with wishes to significantly increase the nutritional status of maize consumers in developing countries. QPM, which has high lysine and tryptophan, holds the security of improving the nutritional condition of children whose main staple food is maize. It is an alternative food for protein supplement in the diet. QPM has been an alternative to the people who are using synthetic lysine and tryptophan.

#### **6.1 QPM genotypes for stress conditions**

Under stress conditions, the quality of the QPM protein does not vary, but the modifications of endosperm and the content of the proteins vary greatly. To enhance the yield of QPMS under different stress conditions is the major constrain for the breeders. Drought stress affects on QPM yield mainly in grain-filling stage [56]. Some studies reported that the supply of selenium to the plant could reduce the negative effects of the water stress conditions and is considered as the cost-efficient approach to improve the quality and yield of maize [57]. Supplying nitrogen and sulfur results in the enhanced growth and yield of QPMs [58]. Some

*Maize - Production and Use*

compared with normal maize [32].

**5.1 Genetics of QPM**

**5. Efforts in enhancing QPM production**

90%, whereas QPM has about 80% value [35].

endosperm and germ, whereas it is 9.25% in normal maize with contribution of 7.9 and 1.28% from endosperm and germ, respectively [18]. An improvement of protein quality has been correlated with the presence of the opaque-2 mutant gene [31]. Crude protein of QPM was higher than the normal maize, and the proportional contribution of the germ is lower in QPMs than with normal varieties. These structural and biochemical changes that happen in the kernel lead to the modifications of the protein profile, both in content and structure, and therefore on the functionality of the protein extracted from QPM [30]. Based on the chemical component analysis, QPM whole kernels showed highest protein content

QPM contains the mutation at opaque-2 loci, which changes the protein composition of the maize endosperm, resulting in increased concentrations of lysine and tryptophan [33]. The increase in concentration (60–100%) of these two essential amino acids increased the biological value of QPM (80%), when compared to normal maize (40–57%) [34]. The biological value of cow milk protein was about

QTL mapping of o2 modifiers insights that it encodes that the 27-kDa - zein protein and it is observed on chromosome-7 long arm [36]. The function of the 27-kDa zein protein in the formation of vitreous endosperm was revealed when the protein quantity increased threefold in QPM compared with soft opaque-2 mutant [37]. An increase in the number of zein proteins and their compaction between starch grains is partially involved in endosperm modification in QPM [38]. The o2 modifier genes have complexity in inheritance [12]; it reveals that several other loci control the formation of a vitreous kernel in QPM. For identifying the other factors linked to the endosperm modification, [39] performed a proteomic study of the non-zein proteins, and it was observed that the quantity of a starch synthesis enzyme and the amylopectin branching structure are changed in QPM. It is supported that QPM starch expands more than normal maize. It reveals that suppression of the opaque

endosperm in QPM was associated with the starch grain properties.

Maize protein quantity can be enhanced with the opaque-2 (o2) mutation, which increases the lysine and tryptophan levels by decreasing the synthesis of zeins. The QPM utilization mainly restricts due to chalky and soft texture kernels [3]. The quality protein maize was developed based on introgression of opaque-2 QTLs, called o2 modifiers which convert to hard and vitreous endosperm [40]. QPM development has significantly improved the status of nutrient-deficient people who suffer from malnutrition and protein energy deficiency in the develop-

Although QPM breeding has been practiced for more than 60 years, genetic mechanism and genetic components controlling endosperm modification are not clearly understood. Opaque-2 (o2) modifier loci have been distributed on six chromosomes [26]. The opaque-2 modification is positively correlated with 27-kDa γ-zein in an F2 population and recombinant inbred lines (RILs), which are produced through crosses between QPM and an o2 mutant as parents [42]. Gene silencing

**36**

ing countries [41].

**6. Breading efforts in QPM**

QPM have the potential to resist some biotic stresses that are caused by some diseases and pests, but the development of QPMs that has resistance to pest or diseases that attack the grains got more importance. Thus the CIMMYT developed the QPM varieties that are resistant to some viruses and are distributed to the National Agricultural Research System (NARS) breeders that are present at different countries in 2002 [59]. During the breading process of QPMs, multiple genes are involved in enhancing the yield of grains, whereas nonadditive gene actions are highly involved for inheritance of the trait. QPM hybrids that are evaluated under salt-, drought- and *Striga*-affected conditions showed nonadditive gene action [60]. Different varieties of QPM genotypes that adapt to the environmental conditions of sub-Saharan Africa were developed by the CIMMYT (2005), and thus great benefits for children have been documented [61]. QPM hybrids could help the poor people for elevation of malnutrition in developing countries.
