Evaluating seed systems to guide improvement: Variety diffusion, disease management and benefits

Seed systems play an important role in the distribution of high-quality seed and improved varieties. The structure of seed networks also helps to determine the epidemiological risk for seedborne disease.

Scientists working in the seed system cluster of the CGIAR Research Program on Roots, Tubers and Bananas (RTB) have been working to support improvements to seed systems and ensure that they provide benefits to all stakeholders.

The RTB team and their collaborators have developed an RTB seed systems toolbox for understanding and improving seed systems, which are generally informal in many parts of the world and have the potential for spreading seedborne diseases.

Two of these tools are the impact network analysis (INA) and the integrated seed health (ISH) approaches and models.

INA provides scenario analyses for comparing the likely outcomes for different decisions about seed systems for all stakeholders.

A recent webinar provided more information and examples for impact network analysis. ISH provides recommendations for how best to integrate the range of disease management options.

An early application of INA was to evaluate the epidemiological role of nodes in seed networks and apply it to a regional potato farmer consortium — Consorcio de Productores de Papa (CONPAPA) in Ecuador.

They surveyed farmers to estimate the structure of networks of farmer seed tuber and ware potato transactions, and farmer information sources about pest and disease management.

Then, they simulated pathogen spread through seed transaction networks to identify priority nodes for disease detection.

The likelihood of pathogen establishment was weighted based on the quality or quantity of information sources about disease management.

CONPAPA staff and facilities, a market and certain farms are priorities for disease management interventions such as training, monitoring and variety dissemination.

Advice from agrochemical store staff was common, but assessed as significantly less reliable. Farmer access to information (reported number and quality of sources) was similar for both genders.

However, women had a smaller amount of the market share for seed tubers and ware potato, a point for improvement in the system.

They continue to update and add new options to the INA platform, with update information at the Garrett Lab website from the University of Florida.

Georgian potatoes. Photo credit: Kelsey F. Andersen Onofre.

RTB teams working in the Republic of Georgia used three tools — the multi-stakeholder framework, ISH and INA — to provide recommendations to national programs for improving potato seed systems.

Potato is very important in the country for enhancing the livelihoods and food security of smallholder farmers.

Key considerations in this system include phytosanitary protections for emerging diseases such as potato wart, and the analysis also evaluated risk due to cropland connectivity.

Using a related approach and more extensive analyses of epidemic risk, RTB teams also evaluated sweetpotato seed systems in Northern Uganda.

This study found that sweetpotato vine sellers formed a network, with 27 sellers and almost 1,000 buyers, organized by village: most sellers had few links, while a few sellers had many links.

They used this network to study, among other things, how to control an epidemic if a pathogen is introduced.

Quarantining villages or managing the disease intensively, so that it could not spread, would obviously help contain a disease, and the more villages are managed, the slower the disease spread. But which villages?

The simplest metric — how many incoming links does a location have — proved almost as effective as more complex criteria, and much more effective than just managing villages at random.

However, management was effective only if 15 or more villages were managed so that they wouldn’t spread disease through the network.

Diagram about the Georgian potato study; From Andersen Onofre et al., 2021.

Resistance genes are a major tool for managing crop diseases, and seed systems should help distribute resistance genes where they are needed.

The networks of crop breeders who exchange resistance genes and deploy them in varieties help to determine the global landscape of resistance and epidemics, an important system for maintaining food security.

They evaluated the general structure of global crop breeding networks for cassava, potato, rice and wheat.

All four are clustered, due to phytosanitary and intellectual property regulations, and linked through CGIAR hubs.

Cassava networks primarily include public breeding groups, whereas others are more mixed. These systems must adapt to global change in climate and land use, the emergence of new diseases and disruptive breeding technologies.

Research priorities to support policy include how best to maintain both diversity and redundancy in the roles played by individual crop breeding groups (public versus private and global versus local), and how best to manage connectivity to optimize resistance gene deployment while avoiding risks to the useful life of resistance genes when specific genes are too commonly used. Good seed systems are key to successful use of resistance genes globally.

In conclusion, new tools in the RTB toolbox, like INA and ISH, support planning for improvements to seed systems and seed health management.

Simpler approaches to obtaining data about systems, such as use of expert elicitation in the Republic of Georgia, can provide important input for national planning.

More detailed analyses of seed systems, drawing on other tools in the toolbox such as seed tracing and the Seed Tracker to provide input for INA and ISH, can provide targeting for epidemic management and identify which stakeholders may need system changes to achieve full benefits from seed systems.

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