**6. Lysine: potential source for food security**

Due to breeding of modern maize hybrids for higher yields at the cost of protein, the grain composition has inadvertently trended to higher starch content [32]. In addition, as corn grain protein is deficient in some amino acids that are nutritionally important, this decline in the amount of grain protein has further decreased the grain's nutritional quality. Increasing the nutritional quality of maize grain protein, particularly by increasing the content of essential amino acids, such as lysine and tryptophan, is one approach to addressing this issue.

With regard to the nutritional needs of monogastric animals, the most restrictive amino acid in corn grain is lysine. Improving the content of lysine is therefore a primary goal for improving the quality of maize grain. Maize protein's low nutritional content is mainly affected by the amino acid composition of endosperm proteins. Corn protein has a 2.7 percent lysine content, which is slightly below the FAO recommendation for human nutrition. While the germ protein in the whole grain has a sufficient lysine content (5.4%), this is diluted by the far more abundant endosperm proteins, which have an average lysine content of only about 1.9%. This is because 60–70% of endosperm protein is made up of zeins that contain little to no residues of lysine [33]. Likewise, the lack of residues of tryptophan in zein proteins is the explanation for the low content of corn protein in tryptophan. Changing the profile of the grain protein through approaches such as zein reduction and lysinerich protein expression could therefore significantly boost the amino acid balance. Alternatively, by elevating the free lysine level in the kernel, the lysine content of the grain could be increased.

There is overwhelming evidence available showing QPM's nutritional dominance over standard maize. Different QPM feeding studies have been performed where under-nourished children given QPM as the only source of protein showed the same growth as those given modified cow milk formula in the diet [34]. Independent research in various countries reported a 12 percent rise in weight in children eating QPM over traditional maize [35]. A study conducted in Guatemala found that the nutritional value of o2 maize is 90% of milk protein compared to 40% of regular maize in young children [11]. QPM has other nutritional advantages, i.e. a stronger leucine/isoleucine ratio and greater niacin availability, with a double increase in tryptophan and lysine and a doubling of biologically functional protein [36]. Even though QPM and normal maize have the same niacin levels, the low leucine content in QPM helps to release more tryptophan for niacin biosynthesis. Thus, pellagra is substantially reduced by QPM [26].

Several animal feed experiments were also performed to test QPM's nutritional benefits and biological superiority. It was first seen in rats where a threefold increase in growth rate was observed when fed a 90% QPM diet. Rats fed with the QPM diet weighed more and were thicker, longer, denser and stronger than ordinary maize diets [37]. The nutritional benefits of QPM have also been systematically carried out in pigs. In pigs raised on QPM, the weight gain was doubled compared to those feeding on only standard corn [38]. Pigs fed with a QPM diet alone with supplements of vitamins and minerals increased twice the rate of normal maize fed by pigs [39].

### **7. Provitamin-a-biofortified maize (PVABM): future food**

One of PVABM's benefits is that it is cheaper than other vitamin A supplements [40]. There is a lower production cost in subsequent years after the crops have been bred and grown, given the necessary storage conditions. In addition, there is no need for additional fortification or vitamin modifications in people's diets once maize has been produced at the farm level [41]. Staple crops, such as maize, are used in rural communities to prepare various meals, so changes in nutrients can stabilize the nutrient composition within them [42]. Under smallholder farming systems, biofortification targets staple crops [43]. To improve the acceptability and

*Breeding Maize for Food and Nutritional Security DOI: http://dx.doi.org/10.5772/intechopen.98741*

accessibility of vitamin A at the household level, various maize products can be developed through PVABM. In rural communities, where maize is used for various goods, the production of PVABM can boost the local economy by people selling snacks, and can improve food security by allowing different meals to be eaten at different times, resulting in decreased VAD in children. There is no doubt that PVABM will boost the food security status of rural households and alleviate VAD, but the willingness of smallholder farmers to embrace PVABM and the acceptability of these products by consumers is a challenge before it can be integrated into smallholder farming systems. Yellow maize is commonly confused with orange maize by rural populations, which could be a major challenge given the perceptions surrounding yellow maize. Across the African continent including South Africa, PVABM has drawn attention from researchers in various fields [44]. In rural areas, where the target groups are mostly located, PVABM has the potential to alleviate VAD, hidden hunger, and boost food security. In order to fix VAD, the carotenoid content in PVABM is essential.

#### **7.1 Carotenoids in PVABM**

In the form of provitamin A, maize grain produces various forms of carotenoids [45] and are present in yellow and orange maize. The carotenoid pigments present in yellow and orange maize result from xanthophyll and carotenes, and are responsible for the endosperm color (yellow or orange). In PVABM, the most abundant carotenoids have been described as β-carotene and β-cryptoxanthin, while alphacarotene is present in smaller capacities. The amount of carotenoids increases with the change in color [46]. Dark orange maize has higher carotenoid levels than other colored maize, but orange and dark orange maize are still not available to farmers and consumers.

#### **8. Genomics-assisted breeding**

Genomics-assisted breeding (GAB) for crop improvement initiates with identification of genomic markers linked with QTL or gene(s) related to the target trait and then the application in the breeding platform. Various GAB strategies have been used in crop improvement, including marker- assisted backcrossing (MAB), marker-assisted recurrent selection (MARS), and genomic selection (GS). Recently, speed breeding is included to the list.

#### **8.1 Marker-assisted backcrossing and recurrent selection**

Marker-assisted backcrossing (MABC) is the introgression of a genomic region (QTL or locus or gene) contributing the desired trait from a donor genotype into a breeding line or elite cultivar without linkage drag through back- crossing after multiple generations. The resultant product of MABC contains the whole genome of an elite parent with the genetic loci or QTL or gene(s) contributing to the desired phenotype from the donor parent [47]. Quantity of molecular marker used, the strength of marker association with the phenotype, undesirable linkage drags, and size of the population used for each generation of back- crossing determines the efficiency of MABC. This method has been used extensively to generate superior lines of varieties for biotic and abiotic stress tolerance. The marker-assisted recurrent selection (MARS) was introduced to counter the inefficiency of MABC in transferring multiple QTLs regulating complex traits like yield or broad-spectrum disease resistance. MARS involves the detection and selection of large QTLs or

multiple genomic regions controlling complex agronomic traits within a single or across the populations and their pyramiding in a single genotype [48]. This approach makes use of the F2 population and is most effective for cross-pollinating species. In disparity with MABC, favorable alleles may be contributed by both the parents, and the selected improved genotype becomes the chimera of their parents. The superior allele enrichment involves the phenotypic and marker effect for desired traits in the F2 population, followed by two or multiple cycles of markerassisted selection [49]. In the past few years, the Hyderabad situated International Maize and Wheat Improvement Center (CIMMYT) has made significant headway in the development of drought-tolerant maize inbred lines through MARS approach in their Asia Maize Drought Tolerance (AMDROUT) project.

#### **8.2 Genomic selection and speed breeding**

Genomic selection (GS) or genome-wide selection (GWS) employs large-scale DNA markers throughout the genome for developing superior germplasm lines. The genomic selection approach has the potential to express multiple QTLs/ genes which are widely distributed throughout the genome. Vigorous phenotyping is not necessary to develop a breeding population, and subsequent offspring selection is based on genotypic predictions, which combines both the genomic and pedigree data for several generations of the breeding cycle [50]. The sum of the information index with a combined effect of genome wide molecular markers called the Genomic estimated breeding value (GEBV), is the basis of recurrent selection [51]. High- density molecular markers where each QTLs is in linkage disequilibrium with a marker is necessary prerequisites for precise GEBV, and thus, for GWS. The success of GS mainly depends on the quantity and diversity of the training population (breeding lines selected for the GWS programme). The reduced number of selection events has decreased the time and cost of breeding. While breeding crops and releasing cultivars for farmers, time is a critical factor as normally it takes 3–7 years for crossing experiments, followed by long evaluation for yield, diseases and quality, and varietal release. Therefore, the approach of modulating day-light and duration for increasing the life cycle, term 'speed breeding', has been introduced. It shortens the breeding cycle by accelerating crop generation in glass- houses and growth chambers by providing controlled rapid growth-promoting conditions [52]. By balancing factors like photoperiod, humidity, temperature, and others we may achieve six generations per year for crops like wheat, barley, canola and chickpea [53]. Also, in the glasshouse, these crops undergo only three generations in a year [53]. Early anthesis in plants was reported grown under speed breeding with fully viable mature seeds with unaffected yield between speed breeding and normal photoperiod conditions in almost all crops [52]. This programme accelerates the generations in mapping population as compared to the duration of MABC/ MARS/GWS, and accelerate the progression towards homozygosity. It has been used in all major crops (annual or biannual), and even in woody shrubs or perennial crops. Reduction of juvenile phase from 5 years to 10 months in apple and 7 to 2 years in chestnut are some of the example of the application of accelerated breeding cycle in perennial crops [54]. Rana et al., [55] has combined marker-assisted selection with speed breeding for developing salt-tolerant rice lines. Jighly et al., [56] coupled Genomic Selection with speed breeding to enhance genetic gains in allogamous plants for example tall fescue. The approach named Speed GS is gaining popularity among breeders for achieving higher genetic gain per cycle, especially for traits with low heritability.
