Seed degeneration of roots, tubers and bananas

potato_SW_ugandaRoots, tubers and bananas (RTB) are vegetatively propagated and therefore accumulate pathogens in successive crop cycles. This reduces the yield and/or quality of products, a process generally referred to as degeneration (or seed degeneration) and is considered to be one of the primary constraints to productivity. In industrialized countries, degeneration of these crops is controlled by clean seed systems, in which pathogen free seed is multiplied under controlled conditions and then sold to farmers. Many projects have been implemented in developing countries to promote similar clean seed systems, but in general these have had little success and most RTB farmers in developing countries rarely if ever buy seed that has been cleaned of these degenerative pathogens.

To address seed degeneration, a project was initiated in the context of the Research Program on Roots Tubers and Bananas (CRP RTB), which is part of the Consultative Group on International Agricultural Research (CGIAR). This CRP involves four CGIAR centers (CIP, CIAT, IITA and Bioversity) and several other research partners. The project also strives to develop capacity for better estimation of the damage caused by degeneration and of the effects of different management strategies on the evolution of pathogens that cause degeneration. A project start-up workshop was held in Arusha, TZ, from 5-8 Feb, 2013.

Dealing with degeneration!

global locations of studies on seed degeneration - potato, sweetpotato, cassava, yam and banana

Click here to see the map of global locations of studies on seed degeneration in 5 staple food crops – potato, sweetpotato, cassava, yam and banana

Seed degeneration is a complex problem associated with different pathogens. By definition, all degeneration causing pathogens are seed borne but not all seed borne pathogens contribute significantly to degeneration because they do not increase in frequency over subsequent generations. Viruses are considered to be a predominant cause of seed degeneration although their relative importance may vary according to the crop and geographical area. Thus addressing the challenges of seed degeneration requires a better understanding of its etiology and epidemiology.

Management of seed degeneration relies on effectively integrating the use of disease-free seed, host resistance and on-farm management tools (such as positive/negative selection, phytosanitation and vector management, among others). The challenge in achieving this however lies in the fact that the success and choice of these strategies are dependent on numerous environmental, economic, biotic and human factors. For example, the use of host resistance as a management tool depends on the robustness of the resistance under varied environmental conditions, pathogen strains, and vector populations, cost and availability of resistant seed, and the acceptance and risk aversion of farmers. Thus understanding the interrelatedness between these factors and the management tools is crucial to managing seed degeneration.

With these questions in mind, this project studies seed degeneration in 5 staple food crops – potato, sweetpotato, cassava, yam and banana. Next generation sequencing techniques are used to study the virome in these crops and better understand the etiology of seed degeneration. The complexity of management is addressed by using computational models to integrate the various strategies and better estimate seed degeneration. Field studies are currently underway to determine the roles of positive selection and host resistance in managing seed degeneration, under variable environmental conditions (view map for details). Ultimately, these studies would contribute to decision support systems that can be used by farmers and/or extension agents to predict the effectiveness of different management strategies in reducing seed degeneration.

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  1. Pingback: Understanding potato seed degeneration to increase yields in Ecuador - RTB-CGIAR

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