Epidemic network analysis for mitigation of invasive pathogens in seed systems: Potato in Ecuador

Abstract

Seed systems have an important role in the distribution of high quality seed and improved varieties. The structure of seed networks also helps to determine the epidemiological risk for seedborne disease. We present a new method for evaluating the epidemiological role of nodes in seed networks, and apply it to a regional potato farmer consortium (CONPAPA) in Ecuador. We surveyed farmers to estimate the structure of networks of farmer seed tuber and ware potato transactions, and farmer information sources about pest and disease management. Then we simulated pathogen spread through seed transaction networks to identify priority nodes for disease detection. The likelihood of pathogen establishment was weighted based on the quality and/or quantity of information sources about disease management. CONPAPA staff and facilities, a market, and certain farms are priorities for disease management interventions, such as training, monitoring and variety dissemination. Advice from agrochemical store staff was common but assessed as significantly less reliable. Farmer access to information (reported number and quality of sources) was similar for both genders. Women had a smaller amount of the market share for seed-tubers and ware potato, however. Understanding seed system networks provides input for scenario analyses to evaluate potential system improvements.

Modeling Epidemics in Seed Systems to Guide Management Strategies: The Case of Sweetpotato in Northern Uganda

“…In this scenario analysis, all nodes (sellers and villages) were assigned an equal likelihood of being the starting point for epidemic introduction. For each possible combination of an epidemic starting node and a sampling node, we determined the number of nodes that could become infected by the time the pathogen is detected at the sampling node, as in Buddenhagen et al (2017). In this analysis we compare only villages, not sellers, for their relative value as locations for epidemic monitoring.…”

“…Seed systems are amenable to network analysis because they are inherently networks with a suite of actors (network nodes) that move both genetic material and information through space and time (dynamic or static network links) (Pautasso 2015). Until recent years, plant disease epidemiologists have given relatively little attention to the study of seed system (and plant trade) networks, although the movement of planting material plays a fundamental role in the spread of plant disease and the persistence of epidemics (Buddenhagen et al 2017;Garrett et al 2017;McQuaid et al 2017;Nelson and Bone 2015;Pautasso 2015;Pautasso and Jeger 2008). Increasing availability of computational tools, coupled with advances in network analysis in the medical and social sciences, makes the implementation of network analysis for plant disease epidemiology more obtainable.…”

“…Our study draws on concepts developed for studying epidemic spread in hypothetical and empirical large-and small-scale plant trade networks (Buddenhagen et al 2017;Moslonka-Lefebvre et al 2011;Nelson and Bone 2015;Pautasso 2015;Pautasso and Jeger 2008;Pautasso et al 2010). We consider theory about the influence of node in-and out-degree on variety dissemination (and pathogen transmission) in small-scale, real-world seed networks (Pautasso 2015).…”

Management performance mapping and the value of information for regional prioritization of management interventions

“…Here we use experimental data about yield under positive selection (as 273 opposed to roguing or random seed selection), at different altitudes and for certified seed that has 274 been propagated for three seasons or less than three seasons. The two most important ware potato varieties 277in Ecuador, Superchola and Fripapa, were sold at a ratio of 2:1 by volume by growers in a 278 cooperative in Tungurahau, Ecuador(Buddenhagen et al 2017), and there was a similar ratio of 279 farmers growing each type. For this illustration, let us ignore the other 14 varieties that were 280 grown in this cooperative, as the volumes reported were less than 10%.…”

“…We consider variety, altitude, and management by estimating mean per plant yields 282 under different conditions, and by using recursive partitioning in rpart. The observed proportion 283of Ecuadorian farmers using certified seed was reported at 2%(Devaux et al 2010), though for 284 some organized groups the proportion can be as high as 46%(Buddenhagen et al 2017). In 285 summary, the reported ratios for this example are as follows: farm altitude (high to low, 51:49), 286…”