Breeding maize genotypes for fall armyworm (Spodoptera frugiperda Lepidoptera: Noctuidae) resistance through conventional approaches: A systematic review
This systematic review, following PRISMA 2020 guidelines, evaluates conventional breeding approaches for fall armyworm resistance in maize within Sub-Saharan Africa, identifying significant progress through methods like recurrent selection and backcrossing while highlighting critical constraints such as limited funding and infrastructure that must be addressed to sustain smallholder food security.
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In the vast agricultural landscapes of Sub-Saharan Africa, maize is more than just a crop; it is the foundation of daily life, providing energy for millions and supporting the livelihoods of hundreds of millions of small-scale farmers. For generations, the stability of this food supply has been threatened by pests, but a new and aggressive invader arrived in 2016: the fall armyworm. This insect, native to the Americas, moved rapidly across the African continent, capable of devouring maize leaves and causing yield losses that can exceed forty percent. While farmers have tried to fight back with chemical sprays, these methods are often too expensive, harmful to the environment, and increasingly ineffective as the pests develop resistance. In regions where genetically modified crops face regulatory and social hurdles, the most reliable path forward lies in the plants themselves. Scientists have long known that some varieties of maize possess a natural ability to withstand insect attacks, a trait known as host plant resistance. This resistance is not a single switch that turns a plant into an impenetrable fortress, but rather a complex, inherited set of defenses that make the plant less appealing or less nutritious to the hungry larvae, allowing it to survive and produce grain even when under attack.
A team of researchers from universities in the Democratic Republic of the Congo set out to map the progress of using traditional breeding methods to harness these natural defenses. They did not invent new genes or rely on laboratory modifications; instead, they conducted a systematic review of existing scientific work to understand how conventional breeding has been used to create maize varieties that can survive the fall armyworm. By gathering and analyzing data from thousands of studies, they identified forty-four key reports that focused specifically on breeding maize for resistance in tropical and subtropical conditions. Their work confirms that while the challenge is immense, significant strides have been made. The researchers found that breeders have successfully identified specific maize lines and populations that carry the genetic traits needed to resist the pest. These resistant sources were often discovered by looking at maize that had already been bred to fight off similar insects, such as stem borers, suggesting that nature often provides overlapping solutions to related problems.
The study reveals that the genetic blueprint for this resistance is complex. Unlike a simple trait controlled by a single gene, resistance to the fall armyworm is governed by many genes working together, some adding up their effects and others interacting in more intricate ways. Because of this complexity, the researchers found that breeders must use specific strategies to move these traits into high-yielding varieties. They rely on structured mating designs, which are careful plans for crossing different plants to see which combinations produce the strongest offspring. Some approaches focus on gradually building up resistance over many generations, while others aim to create hybrid varieties that take advantage of the vigor seen when two different lines are crossed. The review highlights that the most successful programs have been those that combine these traditional crossing methods with a deep understanding of how the environment influences the plant's defenses. A variety that resists the pest in one location might struggle in another, depending on rainfall, temperature, and the intensity of the infestation.
Despite these successes, the path forward is not without obstacles. The researchers noted that many breeding programs in Sub-Saharan Africa are held back by a lack of funding, insufficient infrastructure, and a shortage of specialized experts. Setting up controlled environments to test thousands of plants against the pest is labor-intensive and expensive, and many national programs struggle to maintain the facilities needed for this work. Furthermore, there is a heavy reliance on international centers to provide the initial resistant seeds, which can sometimes lead to varieties that are not perfectly suited to local farming conditions. The study suggests that while the genetic potential exists, realizing it requires a concerted effort to strengthen local research capacities and improve the tools used to screen for resistance.
The review concludes that conventional breeding remains the most accessible and sustainable strategy for protecting maize in Africa. It is a method that does not require expensive technology or complex regulations, making it suitable for the smallholder farmers who feed the continent. The researchers found that by continuing to identify and cross the best resistant lines, breeders can develop varieties that offer both protection against the fall armyworm and the high yields farmers need. While the work is far from finished, the evidence gathered in this review offers a clear roadmap: by understanding the complex genetics of resistance and investing in the people and facilities needed to test them, it is possible to secure the food supply for millions. The future of maize in Sub-Saharan Africa depends on these steady, methodical efforts to turn nature's own defenses into a shield against one of its most destructive pests.
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