Sara Thomas-Sharma, a post-doctoral researcher at Kansas State University, was hired in 2013 to work on an RTB project to model seed degeneration – the build-up of pathogens in planting material. She received an NSF-BREAD Idea Challenge Award, which allowed her to travel to India and Tanzania and address some of the knowledge gaps on seed degeneration by surveying local experts and visiting a field site. An account of her findings follows:
The vegetative planting material of RTB crops is a notorious source of pathogens in many developing countries, causing significant yield reductions. Since numerous factors affect the build-up of pathogens in seed material, understanding these complex processes in an agricultural system can be quite challenging, especially due to the shortage of data on the subject.
Between December 2013 and January 2014, I travelled to India and Tanzania to survey over 20 experts about the factors affecting seed degeneration in their country and crop of expertise. The scientists’ opinions reflect the published and unpublished information that they have integrated through the course of studying particular agronomic systems for many years. If systematically collected and synthesized, such surveys can reduce knowledge gaps and provide preliminary data to hone hypotheses, and prioritize research and development goals.
In general, the experts I surveyed expressed greater uncertainty about estimates involving intricate biotic interactions such as yield loss based on end-of-season infection levels, and disease incidence at varying starting-levels of infection. Some cassava experts in India stated that it is difficult to obtain good yield loss estimates for cassava because there are no healthy cassava plants for comparison. They said cassava mosaic disease is so rampant in India’s cassava growing regions that most farmers have learned to live with it. In contrast, experts had lower uncertainty about providing estimates on management traits, such as adoption of individual management practices and farmer selection skill. Experts classified most of the acreage of RTB crops to be under very low levels of management application (Fig. 1). The ability of farmers to recognize disease symptoms was generally classified as low, although some experts mentioned that farmers recognized plants severely affected with banana bunchy top disease, since yield loss can be dramatic, and cassava mosaic disease, because it has been around for a long time.
Collaborative field experiments studying some of the interactions between biotic and abiotic factors and management practices are currently underway at multiple locations in CGIAR and other research institutes. I was able to visit a cassava seed degeneration trial established in Tanzania by the International Institute of Tropical Agriculture (IITA). This visit to a field site and my in-depth discussions with experts provided me with an excellent opportunity to understand the complexities of field management of seed degeneration. I will expand my initial expert elicitation exercise to include more information on other factors affecting RTB seed systems. This deeper understanding will assist me and my colleagues in building decision support systems to improve management of seed degeneration.