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Social determinants and ecological impacts of seed transmission systems in African root and tuber crops, and their implications for resilience of smallholder farming systems

Final Report Summary - KINSEED (Social determinants and ecological impacts of seed transmission systems in African root and tuber crops, and their implications for resilience of smallholder farming systems)

Informal seed exchange networks are a central feature of smallholder farming communities, and a key resilience mechanism for allowing traditional farming systems to buffer the effects of unpredictable environmental changes. Seed exchange allows farmers to acquire new crop varieties, recover lost varieties, renew their seed stocks, or compensate for seed shortage. However, the contribution of seed exchange to smallholder farming systems’ adaptive capacity remains unclear.
Using case studies from Central and East Africa, this Marie Curie IEF project ‘KINSEED’ investigated the social factors involved in the adoption and dissemination of new crop varieties, and evaluated the role of seed exchange networks in conferring resilience to smallholder farming systems.
In the first component of the project, we studied whether social structures (kinship systems) and local networks of seed exchange influence spatial dynamics of plant virus diseases. Many crop diseases are propagated mechanically through infected stem cuttings that are moved around through farmers’ informal seed systems. In Africa, the Cassava Mosaic Disease (CMD) and Cassava Brown Streak Disease (CBSD) are major threats to regional food security and cause vast economic losses to staple crops. CMD and CBSD both originated from East Africa and have been steadily expanding westwards towards Central and West Africa. Resistant varieties have been widely deployed across Africa in a bid to contain the pandemics. However, lack of empirical data on the influence of social structures on the circulation of crop varieties and seedborne pathogens may limit the effectiveness of agricultural programmes aiming to control the spread of the diseases.
We conducted a next-generation sequencing (NGS) based metagenomics diagnostic study of cassava material from Gabon, central Africa, to estimate and compare CMD prevalence and pathogen load in societies with contrasting social structures. Using a phylodynamic framework combined with social network analysis, we investigated regional virus movements and the evolution of CMD prevalence from epidemiological data collected in 2006-2007 and 2014-2015. Data revealed that differences in the degree of connectivity of farmer communities (i.e. how much they interact through seed exchanges) leave distinctive molecular signals on intra- and inter-population levels of DNA polymorphism in virus metapopulations (Delêtre et al., in preparation, a). NGS data show a similar effect on inter-specific diversity, with higher mean species diversity in communities that readily import seeds compared to those communities who rely essentially on a fixed array of crop varieties (Delêtre et al., in preparation, b).
Using a unique dataset combining anthropological, genetic and plant epidemiological data, these results provide the first empirical demonstration of the role played by informal seed systems in the geographic diffusion of crop diseases, and call for reconsidering the importance of the ‘cultural’ dimension of virus ecosystems for understanding the transmission dynamics of crop plant diseases.
The second component of the project aimed at investigating how local seed exchange networks can be harnessed for effective emergency response and long-term capacity building in smallholder agricultural systems, using Malawi as a case-study.
In January 2015, unusually early and exceptionally intense rainfall led to severe flooding in Malawi, causing extensive damage to crops and infrastructures, and leaving tens of thousands of farmers with little or no saved seed. To respond to this humanitarian crisis, the government and several NGOs launched emergency seed distribution programmes to enable farmers to rebuild their seed stocks. In collaboration with Concern Worldwide, an Irish-based NGO that has been actively working with small communities in Malawi since 2002, we are planning to investigate the role of informal seed systems on the effectiveness and long-term impacts of emergency seed relief programmes.
The collaboration with Concern Worldwide is an outstanding opportunity to integrate fundamental research on seed exchanges with applied sciences. Increased food security and resilience to climate shocks and natural hazards is one of Concern’s major goals for farmers and rural communities in Malawi. Using social network analysis and genotyping-by-sequencing, we plan to assess the contribution of local seed systems to the recovery dynamics of smallholder farming systems after January floods, and the long-term impacts of emergency responses on regional crop diversity. The development of this second component is still ongoing, and will contribute to develop indicators of resilience to help designing local/regional strategies for promoting capacity-building in local farming systems and increasing resilience to climate shocks in Malawi.
Seed exchange networks can be a key leverage point for long-term capacity-building in smallholder farming systems in a context of climate uncertainty and increased pressure from plant pathogens. Root and tuber crops represent an important source of calories in the tropics and play a key role for the economic development and food security in developing countries, particularly in Africa where 500 million people rely upon cassava as their daily staple. However, there is still very little research done on seed exchange networks in vegetatively propagated crops. By developing new methods and approaches to combine anthropological, epidemiological and population genetic data, this Marie Curie project sheds new light on the social dynamics of crop diseases, highlighting the importance of seed exchange as an essential component of social-ecological systems, and a pertinent angle to analyse the multiple dimensions of the problematic of resilience in a context of global change.