Modeling Epidemics in Seed Systems and Landscapes To Guide Management Strategies: The Case of Sweet Potato in Northern Uganda
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Date
2019
Journal Title
Journal ISSN
Volume Title
Publisher
Phytopathology
Abstract
Seed systems are critical for deployment of improved varieties
but also can serve as major conduits for the spread of seedborne
pathogens. As in many other epidemic systems, epidemic risk in seed
systems often depends on the structure of networks of trade, social
interactions, and landscape connectivity. In a case study, we evaluated
the structure of an informal sweet potato seed system in the Gulu region
of northern Uganda for its vulnerability to the spread of emerging
epidemics and its utility for disseminating improved varieties. Seed
transaction data were collected by surveying vine sellers weekly during
the 2014 growing season. We combined data from these observed seed
transactions with estimated dispersal risk based on village-to-village
proximity to create a multilayer network or “supranetwork.” Both the
inverse power law function and negative exponential function, common
models for dispersal kernels, were evaluated in a sensitivity analysis/
uncertainty quantification across a range of parameters chosen to
represent spread based on proximity in the landscape. In a set of
simulation experiments, we modeled the introduction of a novel
pathogen and evaluated the influence of spread parameters on the
selection of villages for surveillance and management. We found that
the starting position in the network was critical for epidemic progress
and final epidemic outcomes, largely driven by node out-degree. The
efficacy of node centrality measures was evaluated for utility in
identifying villages in the network to manage and limit disease spread.
Node degree often performed as well as other, more complicated
centrality measures for the networks where village-to-village spread
was modeled by the inverse power law, whereas betweenness centrality
was often more effective for negative exponential dispersal. This
analysis framework can be applied to provide recommendations for a
wide variety of seed systems.
Description
Keywords
Disease control and pest management, Ecology and epidemiology, Postharvest pathology and mycotoxins, Techniques, Virology
Citation
Andersen, K. F., Buddenhagen, C. E., Rachkara, P., Gibson, R., Kalule, S., Phillips, D., & Garrett, K. A. (2019). Modeling epidemics in seed systems and landscapes to guide management strategies: the case of sweet potato in Northern Uganda. Phytopathology, 109(9), 1519-1532. https://doi.org/10.1094/PHYTO-03-18-0072-R