Modern breeding techniques of maize

Maize (Zea mays) or corn is a cereal crop which is grown widely throughout the world. There exist approximately 50 species, which consist of different grain colors (especially white, yellow and red), textures, shapes and sizes. More maize is produced annually than any other grain. All parts of the crop can be used for food and non-food products. In industrialized countries, maize is largely used as livestock feed and as raw material for industrial products. Maize was introduced into Africa in the 1500s and is now the most cereal crop in Sub-Saharan Africa (SSA) and an important staple food for more than 1.2 billion people in SSA and Latin America. Maize plays also an important role in the livelihoods of millions of poor farmers. They grow maize for food, feed and income. These farmers are often too poor to afford irrigation, and are exposed to significant risks of production and income failure.

In 2014, approximately 1000 million tons of maize was produced worldwide, with the United States of America being the largest producer (361 million tons) (FAOstat 2016). Africa produced approximately 75 million tons (7.4%) with South Africa, Nigeria and Ethiopia as the top-3 producers. Worldwide consumption of maize is more than 116 million tons, with Africa consuming 30%. Africa uses 95% of its production as food, while other world regions use most of their maize as animal feed. Ninety percent of the white maize (also tropical maize) consumption is in Africa and Central America, while the yellow maize is preferred in Europe, most parts of South America and the Caribbean.

Production of maize, especially in Africa, is affected by a number of constraints, including a variety of biotic and abiotic stresses, poor soil fertility, lack of access to quality seed and fertilizers, and a poor post-harvest management. As a result, maize yields in many of the SSA countries are often extremely low, averaging approximately 2 tons per hectare, which is only 20% of the average yield obtained in developed countries.

Various species of stem borers rank as the most devastating maize pests in SSA. They can cause 20-40% losses during cultivation and 30-90% losses postharvest and during storage. Other pests in SSA include ear borers, armyworms, cutworms, grain moths, beetles, weevils, grain borers, rootworms and white grubs. Maize diseases in SSA include downy mildew, rust, leaf blight, stalk and ear rots, leaf spot, and maize streak virus. Striga is another important maize pest. This parasitic weed that severely affects yields of maize (and other crops), infests almost 21 million hectares of land in Africa. Yield losses related to this weed ranging from 65 to 92% have been recorded in the Nigerian Savanna. Finally, maize is susceptible to various molds producing mycotoxins that have deleterious effects on animal and human health.

Maize does not tolerate drought well and the grain can rot during storage in tropical climates. In 2015, the drought in Southern Africa has been recognized as the worst in over three decades with seasonal rains delayed by up to 50 days and higher than normal temperatures recorded during the maize planting season. Last year, South Africa produced 25% less maize and is expected to produce 30% less than the 5 year average this year. Low yields are also expected in Lesotho, Swaziland, Mozambique, Zambia, Zimbabwe and Malawi. South Africa will need most probably at least 5 million tons of maize to be imported. The extreme drought is causing the entire food chain system to break down. Farm workers as well as small scale and subsistence farmers are being affected the most and are struggling to keep their animals alive and to have enough income to provide food for their families.

To ensure food security in the future, maize crop improvements such as disease resistance, drought resistance, higher yields etc are necessary. This can be partially done by conventional breeding, but this takes a very long time. Although modern breeding techniques, such as marker assisted breeding (MAB) and quantitative trait loci (QTL) breeding can greatly accelerate this process, one estimates that the minimum number of breeding generations for cross-fertilizing crops such as maize is 17 generations. Therefore, new breeding techniques and biotechnological tools may become essential to assure a sustainable and sufficient production of maize in Africa.

Once a promising new maize hybrid is created, on farm and on site evaluation is necessary. This involves multi-site evaluation, proper registration and, in particular for GM plants, a safety evaluation and risk assessment should also be performed. In 2016, 13 African countries either planted, actively evaluated field trials or transitioned to grant approvals for the general release of various biotech crops (Burkina Faso, Cameroon, Egypt, Ethiopia, Ghana, Kenya, Malawi, Mozambique, Nigeria, South Africa, Sudan, Swaziland, Tanzania and Uganda). However, not all African research institutes are already aware of the different regulatory frameworks. Additionally, once a new maize variety is developed, it is also important to communicate the findings well, not only to the scientific community, but also, and even more importantly, to the farmers, the public and the policy makers. Therefore, a good communication strategy should be developed.