Breeding maize genotypes for fall armyworm (Spodoptera frugiperda Lepidoptera: Noctuidae) resistance through conventional approaches: A systematic review

Maize is the lifeblood of food security for hundreds of millions of people across Sub-Saharan Africa, providing the primary source of energy for daily life and supporting the livelihoods of small-scale farmers. Yet, this vital crop faces a relentless enemy: the fall armyworm, a moth whose larvae devour leaves and stalks with terrifying speed. Since this pest arrived in the region in 2016, it has spread rapidly, threatening to wipe out harvests and deepen hunger. While farmers have tried to fight back with chemical sprays, these often fail, harm the environment, and are too expensive for the poorest families. Scientists have long known that the most sustainable defense lies within the plant itself. By breeding new varieties of maize that naturally resist the worm, researchers hope to create a shield that costs nothing to apply and works every season. This approach relies on the natural genetic diversity of the corn, selecting and crossing plants that show signs of toughness against the insect, rather than relying on expensive technology or chemicals.

A recent systematic review by Kambale Mbusa Héritier brings together decades of scattered research to map out exactly how this traditional breeding is working against the fall armyworm in Africa. The author examined thousands of scientific records, narrowing them down to forty-four high-quality studies that focused specifically on breeding maize through conventional methods. The goal was to understand which breeding techniques are effective, which plant varieties hold the key to resistance, and what obstacles stand in the way of getting these seeds into the hands of farmers. The review confirms that while the task is difficult, steady progress is being made. Researchers have found that resistance in maize is not a single switch that can be flipped on or off, but a complex trait controlled by many different genes working together. This means the defense is partial rather than absolute; the plant does not become immune, but it can withstand the attack well enough to still produce a harvest.

The study highlights that the most successful breeding programs use specific mating strategies to combine the best traits from different parent plants. Scientists use methods like recurrent selection, where they repeatedly cross and select the best survivors to build up a population of tough plants, or backcrossing, where they take a resistant plant and cross it with a high-yielding one to transfer the resistance without losing the crop's quality. The research shows that both the "additive" effects, where genes simply add up their strength, and "non-additive" effects, where genes interact in surprising ways to create new strengths, play a role in how well a plant resists the worm. Because of this complexity, breeders must carefully choose their tools. If the resistance comes mostly from genes that add up, they focus on improving the whole population. If the resistance comes from specific combinations of parents, they focus on creating hybrid seeds that exploit those powerful pairings.

The review identifies several specific sources of resistance that have proven effective. Much of the genetic material comes from international research centers like CIMMYT and IITA, which have spent years developing maize lines resistant to other similar pests, such as the stem borer. It turns out that plants bred to fight one type of worm often show a natural ability to fight the fall armyworm as well. Specific lines, such as those labeled CML71 and CML125, have emerged as strong candidates for resistance. These plants often exhibit traits like "antibiosis," which means the plant produces substances that harm the worm's growth, or "non-preference," where the plant simply does not smell or taste right to the insect, causing it to avoid the crop. Interestingly, many of the most resistant varieties found so far produce white grains, which are preferred by local farmers, though the exact mechanism behind their resistance remains a subject of ongoing study.

Despite these successes, the path forward is not without significant hurdles. The review paints a clear picture of the challenges facing African breeding programs, which often struggle with limited funding, a lack of specialized equipment, and a shortage of trained experts. Creating a resistant variety requires testing plants under controlled conditions where they are deliberately infested with worms, a process that is labor-intensive and requires specific facilities that are rare in many parts of the region. Furthermore, the resistance a plant shows in one location does not always hold up in another, as weather and soil conditions can change how the plant and the pest interact. This means that a variety that works well in Kenya might fail in the Democratic Republic of Congo, requiring breeders to test their work across many different environments to ensure reliability.

The paper also notes that while modern technologies like genomic selection and gene editing offer exciting possibilities to speed up the process, their use in Sub-Saharan Africa is still limited by regulatory barriers and infrastructure gaps. For now, the most reliable path forward remains the careful, traditional work of crossing plants and selecting the best offspring. The review concludes that conventional breeding is not just a viable option but an essential one for securing food in Africa. It suggests that by combining the best available genetic resources with improved testing methods and better regional cooperation, scientists can continue to develop maize varieties that are tough enough to survive the fall armyworm. The work is far from finished, and the pest remains a serious threat, but the systematic effort to harness the plant's own defenses offers a realistic and sustainable hope for the future of African agriculture.