**2.2 Imazapyr-resistant maize for Striga management**

Parasitic Striga invades the roots of maize and other cereals to remove water and nutrients from host plants. Maize cannot resist striga (**Figure 2**), causing stunting,

**Figure 2.** *Severe striga infestation of maize in western Kenya.*

abnormal growth, and small ears, resulting in a yield reduction of 30 to 80% [19]. About 20 million ha of farmland in sub-Saharan Africa is Striga-infested, resulting in over US \$1 billion per year in yield loss and threatening the food security and livelihoods of over 100 million people [20]. Improved maize varieties that resist the herbicide imazapyr (the IR trait) are becoming available, protecting the roots against parasitic invasion [21]. Very low levels of imazapyr (e.g., 30 to 45 g per ha) are applied to maize seeds. However, the application rate is critical because too much imazapyr can harm maize germination and early growth. When used correctly, the herbicide is placed exactly where and when needed to control striga as it starts invading young maize roots.

Imazapyr herbicides are made from the active ingredient imidazoline, mixed with salt to form a stable powder. The herbicide is then coated onto maize seeds using an adhesive. An example of such a seed treatment system is patented under the term StrigAway. IR maize seeds are planted following recommended soil and fertilizer management practices for a growing area. Imazapyr is non-toxic to mammals, but it is important to wear gloves or wash hands when planting the seed manually, as they may be mixed with insecticides. The spread of this technology across Africa has been slower than expected, given the scope of the problem. Where available, agro-input suppliers sell IR maize seed at about US \$3 per kilogram. Yield increases of 1.0 to 3.0 tons of grain per hectare are achieved compared to comparable varieties not protected by imazapyr [22]. An additional benefit is that the Striga seed bank diminishes over time, eventually eradicating striga from croplands [23].

However, this technology is often too expensive for subsistence farmers. A more affordable option is to integrate imazapyr herbicide technology with other measures, such as planting soybeans followed by striga-resistant maize varieties using nitrogen fertilizer and good agricultural practices [24, 25]. The adoption of this technology depends on several factors, including the age and education of the household head, the availability of training and support for farmers, membership in farmer group, the availability of the technology, perceptions based on the social and cultural context, and the political climate [26].

### **2.3 Vitamin a biofortified maize**

Biofortified maize varieties higher in Vitamin A are also becoming more widely available. Maize is a staple food for over 300 million people across Sub-Saharan Africa; however, the widely grown starchy white varieties contain sub-optimal minerals and vitamins. Conventional breeding has improved the content of provitamin A in maize, offering a viable avenue to improve community nutrition. Golden maize contains beta-carotene, lending it a bright orange color (**Figure 3**). These compounds are converted into vitamin A after ingestion. More than 40 of these biofortified varieties have been released across Sub-Saharan Africa [27]. These varieties were originally developed from Central and South American lines naturally rich in provitamin A and then crossed with well-adapted lines holding improved agronomic traits such as disease resistance and drought tolerance.

Unlike biofortified lines, pro-vitamin A is often oxidized and forms off-flavors other maize varieties. Pro-vitamin A biofortified maize offers a cost-effective solution to Vitamin A deficiency in areas where people consume fresh and dried maize [28]. It provides half the daily Vitamin A requirement for adults and costs \$0.8 to \$1.2 per kg of OPV seed [29]. Golden maize contains 8 to 15 parts per million of pro-vitamin A, while conventional varieties do not have this nutrient. Biofortification of maize is a

#### **Figure 3.**

*Biofortified maize (center) rich in vitamin a compared to conventional yellow and white varieties (top and bottom).*

promising approach to combat micronutrient deficiencies in sub-Saharan Africa. Provitamin A biofortified maize is a safe and effective way to improve vitamin A status, and it has been well-accepted by most communities compared to yellow maize, which has associated negative perceptions. With proper policy support, biofortified maize can help address the deficiency of vitamin A in this region. A study conducted by Nesamvuni et al. revealed that introducing a vitamin-fortified maize meal to the meals of African children aged one to three led to positive effects, such as better weight gain and improvements in specific aspects of their vitamin A levels [30]. Different varieties are available for cultivation in lowland and highland elevations and semi-arid and humid climates.
