**4. QPM: an alternative to normal maize**

Quality protein maize (QPM) was developed in the late 1960s [11] and produces 70–100% more lysine and tryptophan than ordinary modern and traditional tropical maize varieties [12]. In addition, QPM nutritional assessment in different locations has demonstrated the consistency of the content of lysine and tryptophan within the recommended range for QPM, considering very diverse types of environmental conditions [13]. In QPM grain, the nutritional content of the protein exceeds that of cow's milk protein. In developing countries, the adoption of QPM will significantly contribute to alleviating malnutrition in maize-based economies [14]. For example, substituting normal maize in stock feeds has been found to be of economic benefit because it needs small amounts or no supplemental protein sources to balance the diet [15]. QPM cultivars may be competitive in productivity with normal maize and should demonstrate stable performance across environments, especially in terms of yield and protein quality characteristics [13]. Combining high yield with high-quality protein content in an elite maize variety has been a great challenge. QPM development faces severe biotic (diseases and pests) and abiotic (drought, heat, low soil pH, low soil nitrogen, etc.) limitations, as with normal maize. Several studies have been performed around the world to alleviate some of these limitations on breeding for QPM resistance to pests and diseases [16] and tolerance to abiotic stresses such as drought, low soil nitrogen, heat stress and combined heat and drought stress [17]. Quite a number of QPM studies have been performed on improving the nutritional performance and disease tolerance of QPM in breeding programs around the world in recent years [18]. The main research emphasis has been on growing the protein content and exploring genetic variability between QPM genotypes and normal endosperm maize varieties. More research, however, needs to be placed on the resistance of QPM varieties to certain abiotic

stresses, such as heat stress, dryness and heat stress combinations, and low soil pH. In Africa, malnutrition is a persistent issue, especially in rural areas where poor people depend on staple foods and have limited access to a diverse diet. Bio-fortified crops bred for enhanced nutritional quality may mitigate nutritional deficiencies if adequate quantities are produced and consumed. The positive effect of QPM on the nutritional status of human consumption and animal feed has been shown by several studies in controlled settings [19]. In order to preserve protein content in grain, lysine or tryptophan levels should be continuously monitored during the breeding period, even if the op2op2 genotype is retained. One way to solve the problem of malnutrition in the world is the consumption of QPM varieties, especially for people who are low in resources and cannot afford other sources of protein for their families. QPM may also be used as an additional food for humans (particularly pregnant women, lactating mothers and young children) and for animal feeding. Moreover, for refugees and other people facing nutritional challenges around the world, QPM flour can also be very useful.
