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Viruses pose a major challenge to sweetpotato production in Tanzania. Use of cleaned-up, virus-tested seed vines distributed through a formal seed system is among the proposed strategies to address this challenge. However, virus-tested seed vines can get infected once in the field and it is not known how they will perform following several seasons of on farm propagation. We assessed the performance of virus-tested seed vines and farmer-sourced seed vines of a susceptible variety, Ejumula, and a relatively tolerant variety, Kabode, over five seasons to understand the trend in root yields, vine yields and virus incidences. The experiments were done in high and low virus pressure areas. The most prevalent viruses were sweet potato chlorotic stunt virus (SPCSV) followed by sweet potato feathery mottle virus (SPFMV) and sweet potato leaf curl virus (SPLCV), respectively. Both farmer-sourced and cleaned-up, virus-tested seed of cv. Ejumula were rapidly infected with SPCSV. The incidence of this virus on Ejumula's farmer-sourced material at the high-virus-pressure area reached 100% by the second season. The incidences for all three viruses remained stable for cv. Kabode across the five seasons. Plants generated from cleaned-up, virus-tested seed had lower incidences for all viruses compared to those from farmer-sourced planting material. Virus-tested seed produced significantly higher root yields for cv. Ejumula in the high-virus-pressure site, with a gradual drop across the seasons. The findings show that regular replenishment of clean, virus-tested seed is more economical in high-virus-pressure areas and for more susceptible varieties like cv. Ejumula. They also indicate that farmers may be reluctant to invest in cleaned-up, virus-tested seed in cases where they have virus-tolerant varieties such as cv. Kabode due to lack of obvious virus effect on yields.

Insect-proof net tunnels can help reduce virus infection of clean virus-tested sweetpotato seed produced by decentralized seed producers. However, optimal management is required to maintain both quality and quantity of seed produced. This study investigated the effect of the ratoon cropping technique on vine production in net tunnels and open fields. Virus-tested planting material of two varieties, Kabode and Mataya, were grown in net tunnels and open fields. Each variety had 80 plants per plot, with 40 following the ratooning technique and 40 a replanting technique. The ratooned crop was harvested six times, comprising the initial harvest and five regrowths. This covered 14 months representing six generations of vine production. The number of vines, number of nodes per vine, and vine length were recorded. The number of plants showing virus symptoms was also recorded. The ratoon cropping technique produced more vines compared with the replanting technique in both net tunnels and open fields. Cv. Kabode produced more vines in open fields compared with net tunnels regardless of cropping technique. On the other hand, cv. Mataya produced relatively equal numbers of vines in net tunnels and open fields. Despite ratooning leading to more vine production compared with replanting, the technique led to higher virus incidences on plants grown in the open. This also varied with variety with the highest virus disease incidences being recorded on cv. Mataya. We recommend the ratoon cropping technique for sweetpotato vine production in net tunnels. Replanting technique should be adopted for vine production in the open fields because it acts as a key control strategy for virus infections even for susceptible varieties.

Discussion of seed systems and smallholders' demand for seeds and theories of change through seed systems that contribute to SDGs

Constraints in Seed Systems across crops and CGIAR Centres. Priorities for investment in resilient, equitable, integrated seed systems

Discussion of transformative seed systems that enhance gender equity and a proposal for a CGIAR strategy

Over recent decades international agricultural research has shown that it can generate agricultural technologies with benefits for societies in the Global South that outstrip the investments many times over. However, it has also been shown that the benefits generated are not evenly spread and do not reach some groups of farmers at all. Too often, segments of the intended target populations are left out and these often tend to be those already ‘left behind’. New seeds and varieties are important elements of agricultural technologies and the development of these relies on seed delivery systems to get new varieties to the farming population. Here we argue that a clear analysis of the preferences and needs of farming households and their inherent heterogeneity is required when setting the goals for breeding programmes and designing seed delivery systems. We characterize the differences in demand profiles, which implies different types of seed delivery models that are tailed to context, crop and preferences and the multiple needs of farming households. We point to the implications for organizing and targeting the seed delivery system in order to cater for all. Recognising the existence of diverse demands, developing different seeds and varieties and delivering them through a variety of models asks for clarity on mandates and opens up the opportunities for coordination that will lead to synergies in meeting the UN's Sustainable Development Goals and reach a wider population of farming households.

Seed systems research is central to achieving the United Nations Sustainable Development Goals. Improved varieties with promise for ending hunger, improving nutrition, and increasing livelihood security may be released, but how do they reach and benefit different types of farmers? Without widespread adoption the genetic gains achieved with improved crop varieties can never be actualized. Progress has been made toward demand responsive breeding, however the draft CGIAR 2030 Research and Innovation Strategy fails to recognize the complexity of seed systems and thus presents a narrow vision for the future of seed systems research. This points to the lack of evidence-based dialogue between seed systems researchers and breeders. This perspective paper presents findings from an interdisciplinary group of more than 50 CGIAR scientists who used a suite of seed systems tools to identify four knowledge gaps and associated insights from work on the seed systems for vegetatively propagated crops (VPCs), focusing on bananas (especially cooking bananas and plantains), cassava, potato, sweetpotato, and yam. We discuss the implications for thinking about and intervening in seed systems using a combined biophysical and socioeconomic perspective and how this can contribute to increased varietal adoption and benefits to farmers. The tools merit wider use, not only for the seed systems of VPCs, but for the seed of crops facing similar adoption challenges. We argue for deeper collaboration between seed systems researchers, breeders and national seed system stakeholders to address these and other knowledge gaps and generate the evidence and innovations needed to break through the 40% adoption ceiling for modern varieties, and ensure good quality seed once the new varieties have been adopted. Without this, the achievements of breeders may remain stuck in the seed delivery pipeline.

Non-PR, IFPRI5; CRP3.4; CRP2; 1 Fostering Climate-Resilient and Sustainable Food Supply; 3 Building Inclusive and Efficient Markets, Trade Systems, and Food Industry; Capacity Strengthening, DSGD; PIM, CGIAR Research Program on Roots, Tuber, and Bananas (RTB); CGIAR Research Programs on Policies, Institutions, and Markets (PIM), Farmers who grow vegetatively propagated crops (VPC) face certain limitations in access to seed. Some of these constraints are related to policy, institutions and markets. This user guide describes a tool for conducting seed regulatory framework analysis for VPCs. It addresses quality assurance models (e.g. seed certification) and other regulations that can increase availability and access to quality VPC seed for smallholders. The methods used to collect and analyze the data include literature reviews, analysis of regulatory documents, focus group discussions and validation workshops. Stakeholder consultations through standardized key informant interviews are especially important. The resulting analysis is used to advise policy makers and regulatory bodies.

Non-PR, IFPRI5; CRP3.4; CRP2; 1 Fostering Climate-Resilient and Sustainable Food Supply; 3 Building Inclusive and Efficient Markets, Trade Systems, and Food Industry; Capacity Strengthening, DSGD; PIM, CGIAR Research Program on Roots, Tuber, and Bananas (RTB); CGIAR Research Programs on Policies, Institutions, and Markets (PIM), Potato ranks second staple food crop in Kenya. The Government seeks rapid yield growth in the potato subsector, however with only 2% of potato seed planted currently certified there is a persistent shortage of quality seed. There is no consensus on an appropriate model for quality seed assurance which can ensure increased availability and access to quality seed by smallholder farmers, while minimizing risk of spread of plant diseases. This study addressed the question of whether the current seed regulatory framework in Kenya and its implementation meets the need for increased availability and access to quality seed potato, for who, and with what consequences? Secondary data and policy analysis were complemented by semi-structured interviews and focus group discussions involving 72 stakeholders from public, private and civil society conducted in the major potato production areas, and at national level. Our findings show a range of different actors have different and sometimes conflicting interests. Seed potato needs to be produced on a large-scale with enough land and resources to meet rotation and isolation standards and inspection costs. However, this has implications for equitable participation in the seed potato industry. Current regulatory and inspection procedures are perceived by small-scale seed producers as policing rather than facilitating quality seed production. This highlights compromises between achieving short term food security and managing risk of spread of plant diseases. The feasibility of different approaches to manage bacterial wilt and potato cyst nematode are discussed with implications for different scales of seed production. Several policy options are reviewed, with their trade-offs, emphasising the need to for inclusive stakeholder consultations to negotiate towards a common interest space.

Non-PR, IFPRI1; CRP2; CRP3.4; 1 Fostering Climate-Resilient and Sustainable Food Supply; 3 Building Inclusive and Efficient Markets, Trade Systems, and Food Industry; 5 Strengthening Institutions and Governance, EPTD; DSGD; PIM, CGIAR Research Program on Policies, Institutions, and Markets (PIM); CGIAR Research Program on Roots, Tuber, and Bananas (RTB), In many developing countries, smallholder farmers cultivating vegetatively propagated crops (VPCs) have limited access to quality planting material. This constraint can limit both the yield of and returns on VPC cultivation. Yet policy and regulatory initiatives designed to strengthen access to quality VPC planting materials have been relatively unsuccessful to date. Part of the problem is the unique biological and economic characteristics of vegetative propagation and its distinctness from cereal crops, which dominate narratives on seed system reforms. Drawing on qualitative analysis of policy and practice, this study examines reform options related to quality assurance regulations in four crop-country combinations: cassava in Nigeria and Vietnam, and potato in Kenya and Vietnam. The study highlights theory and evidence on existing models of regulation; alternative models that may better incentivize cost-effective multiplication and distribution; and recommendations for policy, regulation, and investment in VPC seed markets. Findings indicate that regulations designed around strict and centralized quality control systems tend to limit market size, while more localized production systems are limited by both capacity and reach. These findings suggest the need for alternatives that balance a permissive regulatory regime with decentralized production systems, grassroots capacity development, market surveillance, and systems that integrate internal (producer-level) quality assurance with external (regulatory) quality assurance.

Farmer-based seed multiplication is widely promoted by development practitioners, but there is limited understanding of the individual or collective motivations of farmers to engage or disengage in specialised seed production. The objective of this study is to understand the factors influencing the continuity of sweetpotato vine multiplication enterprises in the Lake Zone of Tanzania, five years after support from a project ended. A total of 81 out of 88 trained group or individual decentralised vine multipliers (DVMs) were traced to assess their vine multiplication activities. Qualitative and quantitative data were collected through telephone and field interviews. Our data showed that 40% of the 81 DVMs had sold vines in the year prior to the study and 20% had maintained the improved varieties for their own use. Some group members had continued vine sales as individuals. The DVMs' reasons for abandoning vine multiplication included climatic and water access issues, market factors and group dynamics. The DVMs did not engage in high volumes of commercial sales. Socio-economic norms and values underpin the transactions of sweetpotato vines. These norms may undermine the emergence of commercially viable enterprises yet seem navigable for a substantial number of the DVMs. Group DVMs seem less commercially successful than individuals.

We examined the effect of multidimensional farmers’ beliefs on the likelihood of cultivating planting materials of biofortified orange-fleshed sweetpotato (OFSP) varieties. Using a panel dataset and combining difference-in-differences regression with propensity score matching, results showed positive effects of beliefs related to health benefits, yielding ability, sweetness, disease-resistance, storability, early maturity, colour, and that children enjoy eating OFSP roots, on cultivation of OFSP varieties. The proportion of OFSP roots out of total sweetpotato production for a household increased among farmers’ who held these beliefs. Efforts to promote biofortified crops can, therefore, benefit from taking farmers’ multidimensional beliefs into consideration.

Seed systems for roots, tuber, and banana (RTB) crops receive relatively little attention from development-oriented research and commercial seed sector actors, despite their importance for food security, nutrition and rural livelihoods. We review RTB seed systems—with particular reference to potato, sweetpotato, cassava, yam and banana —to reflect on current seed system development approaches and the unique nature of these systems. We refer to our own experiences, literature and 13 case studies of RTB seed system interventions to identify gaps in our knowledge on farmer practices in sourcing and multiplying seed, and processes affecting seed quality. Currently, most approaches to developing RTB seed systems favour decentralised multiplication models to make quality seed available to smallholder farmers. Nevertheless, arguments and experiences show that in many situations, the economic sustainability of these models cannot be guaranteed, among others because the effective demand of farmers for seed from vegetatively propagated crops is unclear. Despite the understudied nature of farmers’ agronomic and social practices in relation to seed production and sourcing in RTB crops, there is sufficient evidence to show that local RTB seed systems are adaptive and dynamic. Our analysis suggests the paramount importance of understanding farmers’ effective demand for seed and how this affects the sustainable supply of quality seed from specialized producer-entrepreneurs, regardless of the seed system paradigm. From the case studies we learnt that few interventions are designed with a rigorous understanding of these issues; in particular, what types of interventions work for which actors, where, and why, although this is a necessary condition for prioritizing investments to increase the use of improved seed by smallholder farmers.

IFPRI1; CRP2; Open Access, EPTD; PIM, CGIAR Research Program on Roots, Tuber, and Bananas (RTB); CGIAR Research Programs on Policies, Institutions, and Markets (PIM), Many developing-country farmers cultivating vegetatively propagated crops (VPCs)—crops such as cassava, potato, sweetpotato, and yam—face constrained access to quality planting material. This challenge is distinct from the challenges facing cereal crops, and is associated with both the unique biological and economic nature of vegetative propagation. Although technological solutions exist, there are other limiting factors relating to policies, institutions, and markets that shape VPC seed systems, e.g., quality assurance mechanisms, certification regulations, sanitary and phytosanitary standards, and plant variety protection. This research project aims to provide actionable evidence on policy and investment options to accelerate seed system and market development in countries where VPCs are important to food security and agricultural development. By taking a collaborative and multidisciplinary approach to the research, the project (1) analyzes current policy initiatives and success factors underpinning models that incentivize cost-effective multiplication and distribution of VPC seed to smallholders; and (2) develops a set of crop-specific case studies in Kenya, Nigeria, and Vietnam that encourage closer consideration of more appropriate policy options. This document provides a brief summary of the project and accompanies the key informant interview guides to collect data for analysis purposes.