Because RTB crops are propagated clonally—by planting tubers, suckers, stalks, or vine cuttings—they present common challenges for farmers that include low multiplication rates, perishable planting material and low yield as a result of seed degeneration. Government agencies and non-government organizations (NGOs) have developed seed systems to disseminate improved varieties and high-quality planting material (commonly referred to as ‘seed’), but only a small fraction of smallholders have access to those formal seed systems. To increase farmer access to quality planting material and improve yields, RTB centers have collaborated on cross-crop research to develop tools for improving seed systems and seed degeneration management.
RTB researchers developed a multi-stakeholder, seed systems framework and used it to analyze 13 formal and informal seed systems for five RTB crops in Africa and Latin America, extracting lessons that can be applied across crops and contexts. CIP then used the framework for a scoping study of potato seed systems in Karnataka and Maharashtra, India, identifying bottlenecks that prevent more farmers from gaining access to quality seed potatoes. RTB researchers will make the framework more gender responsive and use it to assess more seed systems in 2017.
Seed degeneration – the transmission and accumulation of pests or pathogens from one seed cycle to the next via planting material – is a major cause of yield loss, and is consequently a priority for RTB. Researchers conducted literature reviews on seed degeneration, developed a theoretical seed degeneration model, and used it to assess the effectiveness of different approaches to managing seed degeneration. This resulted in the development of an integrated seed health strategy, which combines the use of disease-resistant varieties with on-farm management practices such as roguing (removing plants with disease symptoms), positive selection (choosing healthy planting material in-field for the next planting cycle), and strategic replacement of seed with disease-free material.
To better understand the dynamics of seed degeneration, researchers have conducted field trials in different agro-ecologies of eight African and South American countries. The trials used popular varieties of banana, cassava, potato, sweetpotato and yam infected with 11 pathogens and spanned multiple cropping cycles over several years. They included evaluations of common on-farm management practices, producing data on pathogens and vectors, and the effects of weather, varietal resistance levels, seed management, and other agronomic practices on seed degeneration.
The resulting data are being used to develop crop-specific seed degeneration models that scientists can use to predict how varieties will perform in specific agro-ecologies under determined disease pressures, weather conditions and management strategies. They will be used to develop management performance maps and decision support tools that research and extension agencies, and seed producers can use to identify the best options for managing degeneration.
The field research has shed new light on pathogen dynamics and management strategies. For example, potato research in Ecuador demonstrated that reversion (naturally occurring reduction of pathogen incidence within a seed lot) takes place at higher altitudes. Researchers used impact network analysis to study planting material movement in informal sweetpotato seed systems in northern Uganda, completing in silico simulations of the introduction of a novel virus to identify nodes within those distribution networks of importance for disease sampling and mitigation.
“There is a bias against informal seed systems, and most interventions try to create seed systems from scratch,” said CIP seed specialist Jorge Andrade, who coordinates the RTB seed systems research.
It is important to understand the dynamics of informal seed systems and farmer demand for planting material before designing any intervention.
Andrade explained that RTB is developing a toolbox of analytical and diagnostic methodologies that government agencies, NARS, NGOs, and donors can use to improve the design and execution of seed-system interventions and the management of seed degeneration.
Photo: Potato farmers in Ecuador, where research found the incidence of pathogens within a seed lot was naturally reduced at higher altitudes. CIP