Keywords

1.1 Global Importance of Sweetpotato

Sweetpotato is a critical crop in the global agricultural landscape, serving as a key source of nutrition, income, and food security for millions around the globe. Its significance is rooted in its remarkable versatility as a food, animal feed and processing crop, and its nutritional benefits, and adaptability to a wide range of environmental conditions, making it an important food staple for diverse populations, particularly in sub-Saharan Africa (SSA) and Southeast Asia. Sweetpotato has become particularly popular not only due to its health benefits but also for its culinary versatility, being used in a wide variety of dishes ranging from traditional baked and mashed sweetpotatoes to innovative products like sweetpotato purees, fries, chips, pies, breads, and even as an ingredient in health-conscious food products for cattle, poultry, and pet food suppliers.

The global cultivation of sweetpotato is a testimony to the crop's flexibility and its ability to integrate into various agroecological, cultural and dietary circumstances. Each geographic region produces unique varieties of sweetpotato, contributing to the crop's global genetic diversity. This diversity is not only a cultural treasure but also a critical resource for breeding programs aimed at developing new varieties that can meet future challenges.

Sweetpotato is cultivated widely across the globe, spanning tropical, subtropical, and temperate regions. It plays a pivotal role in subsistence agriculture by providing food security and nutrition, while also serving as a cash crop through the sale of fresh produce and value-added products such as snacks, flour, and animal feed in developing and developed countries. The dual role of sweetpotato enhances the economic resilience of farming communities and contributes to rural development and poverty reduction in developing and developed countries. Its ability to thrive in marginal soils and withstand harsh growing conditions, including droughts and poor soil quality, enhances sweetpotato’s potential as a sustainable food source amidst the challenges of climate change and increasing global food demands. Indeed, sweetpotato is often one of the critical crops grown after devasting floods or time of drought in SSA (Loebenstein and Thottappilly 2009; Low et al. 2017; Scott 2021). The adaptability of sweetpotato to diverse environments, coupled with ongoing research and development efforts aimed at improving its yield, disease resistance, and nutritional content, ensures that this crop will continue to be a cornerstone of global food security strategies.

The global production of sweetpotato is dominated by several key countries. According to the Food and Agriculture Organization (FAO) of the United Nations, during the period 2018–2022 the top ten countries in terms of sweetpotato production were: China, Malawi, Nigeria, Tanzania, Uganda, Indonesia, Vietnam, India, United States, and Rwanda (FAO 2024; Fig. 1.1). These ten countries exemplify the global importance of sweetpotato, reflecting its role in sustaining livelihoods, enhancing nutrition, and contributing to economic stability. The International Potato Center, which has a global mandate for sweetpotato improvement and germplasm conservation as a member of the CGIAR (Consultative Group on International Agricultural Research), estimates that sweetpotatoes are grown in over 100 countries.

Fig. 1.1
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Top ten global producers of sweetpotato (FAOSTAT 2018–2022)

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China is, by far, the global leader in sweetpotato production, with the crop playing a crucial role in both the domestic and global supply of the crop (Fig. 1.2). In China, sweetpotatoes are integrated into various cuisines and snacks, and are also used for feed and industrial purposes such as the production of starch-based noodles and alcohol. In the SSA countries of Malawi, Nigeria, Tanzania, Uganda, and Ethiopia, in addition to being valued for its adaptability to different climates and soils, sweetpotato is also vital for food security and nutrition. However, it has also become an essential crop for both consumption and income, with significant production levels reflecting its rising role in the national agricultural sector in many SSA countries. In Vietnam, sweetpotato serves multiple purposes, from direct consumption to use in animal feed and starch production, making it a key agricultural commodity, while in Indonesia sweetpotato is a traditional food source that is increasingly recognized for its potential in food processing and value addition. In the United States, which predominantly produce orange-fleshed sweetpotatoes (OFSP), sweetpotatoes are considered a high value crop and they are increasingly being referred to as a super food by culinary influencers. This has increased the visibility of the crop significantly and sweetpotato production in the United States has seen significant growth over recent years, both in acreage and output, due to the increasing demand for sweetpotatoes as a nutritious and versatile food option. Currently, the U.S. is one of the largest global exporters of sweetpotato, and they are recognized for its high-quality sweetpotato cultivars, due to high quality storage and packing facilities which can provide year-round product to domestic and international markets.

Fig. 1.2
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Production share of sweetpotato by region (FAOSTAT 2018–2022)

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1.2 Sweetpotato, a Nutritional Powerhouse and Potent Economic Driver

Sweetpotato is celebrated worldwide for its exceptional nutritional profile. Indeed, many consumer organizations consider sweetpotato to be a super food, providing a rich source of carbohydrates, dietary fibers, vitamins (especially Vitamin A in the form of beta-carotene in orange-fleshed sweetpotatoes (OFSP)), and minerals, making them an important component in the fight against malnutrition and vitamin deficiencies (Andrade et al. 2009; Scott 2021; Ojwang et al. 2023). The storage roots of sweetpotato come in a diverse array of skin and flesh colors ranging from white to cream, light yellow to deep orange, and light to dark purple. These colors provide consumers a strong visual appeal while also providing valuable health benefits due to the different phytochemicals and antioxidants present in the flesh of the sweetpotatoes, which are renowned for their nutritional benefits as they help to neutralize free radicals in the body, reducing oxidative stress and lowering the risk of chronic diseases (Truong et al. 2018). Along with this remarkable spectrum of colors, the flavor and texture profiles of sweetpotato can vary dramatically, with flavors ranging from very sweet to non-sweet and smooth, creamy to hard, mealy textures due to the starch and α- and β-amylase profiles present in the storage roots. The development and dissemination OFSP varieties have been particularly impactful in SSA, significantly improving vitamin A intake among vulnerable populations, including women of reproductive age and young children (Low et al. 2017; Girard et al. 2021). This nutritional intervention has shown remarkable efficacy in improving health outcomes and reducing morbidity from micronutrient deficiencies, however, differences in the flavor and texture profile of the OFSP varieties have undoubtedly affected adoption of these varieties in regions not accustomed to the slightly sweeter, smoother textures and generally stronger flavor characteristics of the OFSP’s.

Beyond its nutritional benefits, sweetpotato plays a crucial role in the economic livelihoods of millions. In many regions, especially in SSA, SE Asia, and Latin America, sweetpotato is not only a staple food crop but also a vital source of income for smallholder farmers. The crop's short growing cycle, low input requirements, and high yield potential make it an attractive option for resource-poor farmers facing limited access to agricultural inputs and technologies. Furthermore, the burgeoning market for sweetpotato-based value-added products, ranging from processed foods such as sweetpotato fries and chips, to purees, and use as a wheat flour substitute for bread products, and industrial uses such as starch and bioethanol production, opens new avenues for economic development and diversification, contributing to rural development and poverty alleviation. In the US, the value and consumption of the crop has risen considerably during the last 20 years. Currently, the US is the largest exporter of sweetpotatoes in the world (FAOSTAT 2024), with five-year rolling averages of acres harvested and total farm-gate value of the crop increasing 70% and 224%, during the years 1996–2000 and 2019–2023, respectively (USDA-ERS 2024).

1.3 Sweetpotato Crop Resilience and Adaptability Complement Its Nutritional Status and Contribute to Sustainable Agricultural Systems

In addition to its nutritional qualities, one of the most compelling attributes of sweetpotato is its adaptability to a wide range of environmental conditions, which is well exemplified by its subtropical to temperate climate cultivation (Loebenstein and Thottappilly 2009; Grüneberg et al. 2015). An asexually propagated crop planted using un-rooted tip and stem cuttings obtained from vines and/or plant sprouts obtained from storage roots, sweetpotato exhibits remarkable resilience to various stresses, including drought and flooding, poor soil quality, and diseases. This resilience is particularly crucial for food security in vulnerable regions where the impacts of climate change threaten agricultural productivity and food availability. Its ability to grow in marginal soils with minimal water and fertilizer inputs align with the principles of sustainable agriculture, reducing the environmental footprint of food production. Additionally, sweetpotato plays a role in crop rotation and intercropping systems, contributing to soil health and biodiversity, and offering a natural pest and disease management strategy that minimizes the need for chemical inputs. These practices enhance agricultural sustainability, support the ecological balance, and preserve resources for future generations. Through breeding efforts, both traditional and genomic-assisted, new varieties of sweetpotato are being developed that further enhance this resilience, ensuring sustainable food production systems in diverse agroecological zones.

1.4 Major Milestones in Sweetpotato Improvement

Long- and short-term investments by organizations such as United States Agency for International Development (USAID), The McKnight Foundation, Collaborative Crops Research Program, the Bill and Melinda Gates Foundation (BMGF) to the CGIAR via CIP and NCSU, and the Rockefeller Foundation via AGRA (The Alliance for a Green Revolution in Africa) have been instrumental in driving sweetpotato research forward, particularly in the developing world. Additional agencies such as the World Bank, the Food and Agriculture Organization of the United Nations (FAO), the African Development Bank (AfDB), the European Union (EU), and The United Kingdom's Foreign, Commonwealth & Development Office (FCDO) have been pivotable in enhancing the cultivation, nutritional value, and market potential of sweetpotato. These investments have focused on various sweetpotato improvement needs, including improving crop yields, development and promotion of clean seed programs, efforts to enhance nutritional content, and increasing resilience to environmental stresses. Funding through these organizations and many others not specifically named herein, has highlighted the role of sweetpotato in alleviating hunger and malnutrition, particularly in the developing world. These organizations, and their many national and international partners, have played a crucial role in research and development initiatives focused on unlocking the full potential of sweetpotato as a key crop for global food security, nutrition, and sustainable agriculture. This support has enabled significant advances in breeding, pest and disease management, agronomic and seed production practices, and value chain improvements, and it has contributed to the well-being of millions of people, especially in resource-poor settings.

1.5 The Value of Traditional and Genomic-Assisted Breeding in Sweetpotato

Traditional breeding techniques have been the cornerstone of crop improvement for centuries, relying on the selection and crossing of plants to combine desirable traits. In sweetpotato, traditional breeding has typically relied on recurrent phenotypic and/or mass-selection of plants with desirable traits, such as yield, storage root size, shape and color, and resistance to local biotic and abiotic stressors. This has led to the development of varieties that are better tasting, more nutritious, and more resilient to pests and diseases (Grüneberg et al. 2015; Mwanga et al. 2017). However, in a complex functional autohexaploid like sweetpotato, traditional, phenotype-based breeding methods are very imprecise, and it often takes 8–10 years or more to develop and release a new variety. This is much too long in today’s rapidly changing environments and marketplaces. Because of its polyploidy, each new segregating seedling population created through crossing results in a remarkable array of plant types and storage root shapes, colors, and qualities, which can be harnessed by sweetpotato breeding programs to create new varieties. The benefit of this in an asexually propagated crop like sweetpotato is that each genotype has the potential to be a new variety. However, sweetpotato breeding is time consuming and exceedingly difficult because it is hard to generate large populations of materials to exercise selection on as each successful cross only produces a maximum of four botanical seed, and most parents suffer from sporophytic and/or gametophytic incompatibilities, resulting in cross success rates often less than 30%. This means that it is exceedingly difficult to generate the large populations that need to be sampled to find the optimal combination of traits required for a successful new variety to be developed, and while they have resulted in advances, traditional breeding methods take too long to accomplish. Genomic-assisted breeding offers solutions to this problem.

1.6 The Rise of Genomic-Assisted Breeding in Sweetpotato

Genomic-assisted breeding has resulted in major advances in crop improvement and these tools are beginning to impact sweetpotato breeding (Mwanga, et al. 2017; Yan et al. 2022). These topics are addressed thoroughly in the following chapters of The Sweetpotato Genome. By leveraging advances in DNA sequencing, bioinformatics, and molecular biology, genomic-assisted breeding allows for the precise identification and manipulation of genes responsible for specific traits. This precision has great potential to speed the development of sweetpotato varieties with targeted improvements in a fraction of the time required by traditional methods.

Key aspects of genomic-assisted breeding include marker-assisted selection (MAS), genomic selection (GS), and gene editing techniques like CRISPR-Cas9. MAS uses molecular markers linked to desirable traits to accelerate the breeding process, while GS predicts the breeding value of individuals using genome-wide marker data. These approaches can significantly enhance the efficiency of selection for traits such as disease resistance, nutritional content, flavor and texture, and yield. Genomic-assisted breeding also facilitates the exploration of the sweetpotato's complex genome, which is particularly challenging due to its polyploid nature. Understanding the genetic basis of traits allows breeders to make more informed decisions, leading to the rapid development of superior varieties. In the future it is conceivable that gene-editing procedures will be used to “fix” otherwise good cultivars through the introduction of improved traits via gene editing, in a fashion like backcrossing strategies used in many diploid inbred crops.

1.7 Merging Traditional and Genomic-Assisted Tools in Sweetpotato

The integration of traditional and genomic-assisted breeding tools is highly complementary with traditional breeding benefiting greatly from insights provided by genomics, such as the identification of genetic markers associated with desirable traits. An excellent example of this is the development of KASP markers for β-carotene and starch production and root knot nematode resistance in sweetpotato (Chap. 8, Fraher 2022). Conversely, genomic-assisted methods are enhanced by the empirical knowledge of plant phenotypes and environmental interactions gained through traditional breeding. Combining these approaches allows breeders to harness the full spectrum of genetic diversity within sweetpotato. This diversity is a valuable resource for introducing new traits and adapting to changing environmental conditions.

As mentioned earlier, the complex genetics of sweetpotato are a major impediment to rapid development of improved cultivars. Speed and precision can be greatly enhanced through the merging of these technologies. While traditional breeding benefits from the direct selection of phenotypes, it can be slow and is often limited by the genetic complexity of traits. Genomic-assisted breeding offers precision and speed, particularly for traits that are difficult to measure or are influenced by multiple genes, which is common in sweetpotato. The synergy of these methods can be used to accelerate the development of improved varieties (Chap. 12). Climate change, emerging pests and diseases, and the need for sustainable agricultural practices require the rapid development of adaptive, resilient, and nutritious sweetpotato varieties. The integration of traditional and genomic-assisted breeding will enable a more dynamic response to these challenges, while leveraging the strengths of both approaches.

1.8 Future Directions and Challenges of Genomic-Assisted Breeding

The integration of traditional and genomic-assisted breeding in sweetpotato faces several challenges, including the need for capacity building in genomic technologies, especially in developing countries where sweetpotatoes are a major crop. Additionally, ethical considerations and regulatory frameworks for genetically modified organisms (GMOs) and gene-edited crops must be addressed to ensure public acceptance and market access. However, the future of sweetpotato improvement lies in the continued evolution of breeding technologies, including the potential application of artificial intelligence and machine learning to analyze complex genomic and phenotypic data. Such advancements will further enhance the precision and efficiency of sweetpotato breeding, enabling the development of varieties that are not only high-yielding and nutritious but also resilient to the challenges posed by a changing global environment.

1.9 Advances in Phenomics Complement Genomic-Assisted Breeding

Like genomics, advances in phenomics and database development are transforming the way sweetpotato breeding programs operate. Phenomics, the study of phenomes—the physical and biochemical traits of organisms as they change in response to genetic and environmental influences—provides new tools for identifying desirable traits with greater precision and speed. Phenomics has emerged as a cornerstone technology in the field of crop improvement as accurate and reliable phenotyping are so critical to the identification of genes associated with specific traits and comprehensive understanding of how different genotypes respond to environmental stimuli.

High-throughput phenotyping technologies, such as optical imaging via various video and high-speed digital cameras systems, remote sensing using unmanned aerial vehicles (UAV’s) and satellites, visible and non-visible spectroscopy methods such as near infrared spectroscopy (NIRS), high performance liquid chromatography (HPLC) and gas chromatography (GC) for chemicals enable the rapid and accurate measurement of a wide range of sweetpotato traits. These include storage root size, shape, color, nutritional content, and resistance to diseases and pests. By automating the data collection process, researchers can evaluate thousands of plants in a fraction of the time required by traditional methods, accelerating the identification and selection of superior genotypes. Through detailed phenotypic assessments, phenomics are increasingly supporting the development of sweetpotato varieties with improved nutritional profiles, such as increased levels of vitamins, minerals, and antioxidants. Simultaneously, it enables the selection of genotypes that achieve higher yields and better overall crop performance, addressing the dual challenges of nutritional security and food production efficiency.

The proliferation of genomic and phenomic data has necessitated the development of sophisticated databases to store, manage, and analyze this wealth of information. These databases have become integral to the modern crop improvement pipeline, providing a foundation for data-driven decision-making and breeding strategies (Morales et al. 2022). Advanced databases such as those described in Chap. 11 integrate phenotypic data with genomic, environmental, and agronomic information, creating a multi-dimensional resource for researchers and breeders. This integration facilitates improved understanding of the complex interactions between genotype, phenotype, and environment, enabling the identification of traits and genes associated with desirable sweetpotato characteristics. These modern database platforms are designed to be accessible and user-friendly, encouraging collaboration and data sharing among the global research community. By centralizing sweetpotato data, these platforms also foster international cooperation, facilitate the exchange of germplasm and information, and accelerate the pace of crop improvement efforts.

1.10 Summary

In summary, the future is bright for sweetpotato. The concerted efforts of the scientific community, funding organizations, and farmers, coupled with technological advancements in breeding, genomics, and food science, are paving the way for the crop's enhanced role in global agriculture. Sweetpotato has emerged as a key player in the fight against hunger and malnutrition, with its potential being increasingly recognized and leveraged across the world. The transformation of sweetpotato from an orphan crop to one of growing importance is a testament to the power of innovation, investment, and collaboration in addressing some of the most pressing challenges in food security and nutrition. However, the potential of sweetpotato is yet to be fully harnessed. Challenges such as post-harvest losses, limited access to improved varieties, and underdeveloped value chains hinder the crop's contribution to global food security and economic development. Addressing these challenges will require integrated efforts, including research and development, capacity building, and policy support. Likewise, the increasing interest in sweetpotato as a functional food, rich in health-promoting compounds, presents an opportunity for innovation in food systems (Nakitto et al. 2022). As consumer awareness about health and nutrition grows, so does the demand for foods that can deliver health benefits beyond basic nutrition. Sweetpotato, with its rich nutrient profile and potential for biofortification, stands at the forefront of this trend, offering ample opportunities for the development of novel food products and increased income opportunities for farmers globally. Clearly, sweetpotato is no longer an orphan crop, it is a crop that is ripe with economic opportunities.