Pathogen buildup in vegetative planting material, termed seed degeneration, is a major problem in many low-income countries. When smallholder farmers use seed produced on-farm or acquired outside certified programs, it is often infected. We introduce a risk assessment framework for seed degeneration, evaluating the relative performance of individual and combined components of an integrated seed health strategy. The frequency distribution of management performance outcomes was evaluated for models incorporating biological and environmental heterogeneity, with the following results. (1) On-farm seed selection can perform as well as certified seed, if the rate of success in selecting healthy plants for seed production is high; (2) when choosing among within-season management strategies, external inoculum can determine the relative usefulness of 'incidence-altering management' (affecting the proportion of diseased plants/seeds) and 'rate-altering management' (affecting the rate of disease transmission in the field); (3) under severe disease scenarios, where it is difficult to implement management components at high levels of effectiveness, combining management components can be synergistic and keep seed degeneration below a threshold; (4) combining management components can also close the yield gap between average and worst-case scenarios. We also illustrate the potential for expert elicitation to provide parameter estimates when empirical data are unavailable. [Formula: see text] Copyright © 2017 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

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24Pathogen build-up in vegetative planting material, termed seed degeneration, is a major problem 25 in many low-income countries. When smallholder farmers use seed produced on-farm or 26 acquired outside certified programs, it is often infected. We introduce a risk assessment

The geographic pattern of croplands is an important risk factor for the invasion of crop-specific pathogens and arthropods, and saturation by endemic pests. Understanding the structure of cropland networks supports sampling and mitigation strategies. We evaluated global networks of key vegetatively-propagated crops (banana, cassava, potato, sweetpotato, and yam) of particular importance to food security in the tropics. The risk of damage from diseases transmitted through vegetative propagation is a particular concern. We analyzed the structure of cropland networks for each crop, where the existence of a link between geographic location pairs was determined using a gravity model, as a function of the distance between the pair of locations and the product of the harvested crop area in the two locations. Networks were evaluated using a novel index of pathogen or arthropod invasion and saturation risk, based on the role of locations in bridging cropland areas and the degree of connectedness of a location and its neighbors. peer-reviewed)