Kelsey Andersen

Rainfastness of Prothioconazole + Tebuconazole for Fusarium Head Blight and Deoxynivalenol Management in Soft Red Winter Wheat

Fungicides are most warranted for control of Fusarium head blight (FHB), a disease of wheat caused by the fungal pathogen Fusarium graminearum, when wet, rainy conditions occur during anthesis. However, it is unclear whether rainfall directly following application affects fungicide efficacy against FHB and its associated toxin, deoxynivalenol (DON). The objective of this study was to determine the rainfastness of the fungicide tebuconazole + prothioconazole and the residual life of tebuconazole when applied to wheat spikes at anthesis in combination with the nonionic surfactant Induce. Three field experiments were conducted during 2012 and 2013 in Wooster, OH. Simulated rainfall of a fixed intensity and duration was applied to separate plots at five different times after the fungicide treatment (0, 60, 105, 150, or 195 min). Spike samples were collected at 4-day intervals after fungicide application and assayed for tebuconazole residue. A similar set of greenhouse experiments was conducted using six post-fungicide-application rainfall timing treatments (0, 15, 30, 60, 120, or 180 min). All experiments were inoculated at anthesis with spores of F. graminearum, and FHB index (IND) and DON were quantified. In four of the five experiments, all fungicide-treated experimental units (EUs) had significantly lower mean IND and DON than the untreated check, regardless of rainfall treatment. Among rainfall treatments, EUs that received the earliest rains after fungicide application tended to have the highest numerical mean IND and DON, but were generally not significantly different from EUs that received later rain or fungicide without rain. In both years, fungicide residue on wheat spikes decreased rapidly with time after application, but the rate of reduction varied somewhat between years, with a half-life of 6 to 9 days. Rainfall treatment did not have a significant effect on the rate of residue reduction or the level of residue at a fixed sampling time after fungicide application. In this study, tebuconazole + prothioconazole mixed with a nonionic surfactant was fairly rainfast for a fixed set of rainfall characteristics, and tebuconazole residue did not persist very long after application on wheat spikes.

Fusarium Head Blight Development and Deoxynivalenol Accumulation in Wheat as Influenced by Post-Anthesis Moisture Patterns

Mist chamber experiments were conducted to quantify and model the effects of post-anthesis moisture on Fusarium head blight (FHB) index (IND) and deoxynivalenol (DON). Four mist treatments, one daily and three intermittent, were applied during an 8-day window immediately after anthesis, plus an untreated check. All intermittent mist treatments received moisture on 4 of the 8 days, but the distribution of the supplemental moisture during the treatment window varied among the treatments. Separate sets of spikes in each treatment were either spray or point inoculated with a spore suspension of Fusarium graminearum. Based on results from linear mixed-model analyses, mist treatment had a significant effect on arcsine-square root-transformed IND (arcIND) and log-transformed DON (logDON) in spray-inoculated spikes but only a marginal effect on DON in point-inoculated spikes. The daily mist treatments (Mist1) consistently had the highest mean IND and DON but several of the 4-day intermittent mist treatments were not significantly different, particularly for point inoculations. Only Mist1 and one of the intermittent mist treatments (Mist2; 2 days of mist at the beginning and end of the treatment window) had significantly higher infection efficiency (estimated diseased spikelets per spore) than the check; however, none of the treatments increased the rate of disease spread within the spike (based on visual symptoms) relative to the check. For all treatments, there was a significant, positive linear relationship between IND and logDON, with estimated mean regression slopes (rates of logDON increase per unit increase in IND) of 0.04 and 0.02 logDON %(-1) IND for the point- and spray-inoculated experiments, respectively. Mist treatment did not have a significant effect on the slope but had a significant effect on the intercept. The height of the regression line (logDON after adjusting for IND) was consistently higher for Mist2 than for Mist1 for both point- and spray-inoculated spikes. Estimated mean back-transformed DON at a fixed level of IND was 4.9 and 2.9 ppm higher for Mist2 than Mist1 in the spray- and point-inoculation experiments, respectively. Generalized linear mixed models were used to estimate the risk of IND and DON exceeding critical thresholds, showing similar results among treatments in terms of estimated probabilities. The estimated probabilities of IND≥10% at 20 days after inoculation and DON≥2, 5, and 10 ppm were not significantly different between Mist1 and Mist2. These results suggest that post-anthesis moisture patterns may play a role in DON exceeding critical thresholds even when FHB level are relatively low.

Resistance Genes in Global Crop Breeding Networks

Resistance genes are a major tool for managing crop diseases. The networks of crop breeders who exchange resistance genes and deploy them in varieties help to determine the global landscape of resistance and epidemics, an important system for maintaining food security. These networks function as a complex adaptive system, with associated strengths and vulnerabilities, and implications for policies to support resistance gene deployment strategies. Extensions of epidemic network analysis can be used to evaluate the multilayer agricultural networks that support and influence crop breeding networks. Here, we evaluate the general structure of crop breeding networks for cassava, potato, rice, and wheat. All four are clustered due to phytosanitary and intellectual property regulations, and linked through CGIAR hubs. Cassava networks primarily include public breeding groups, whereas others are more mixed. These systems must adapt to global change in climate and land use, the emergence of new diseases, and disruptive breeding technologies. Research priorities to support policy include how best to maintain both diversity and redundancy in the roles played by individual crop breeding groups (public versus private and global versus local), and how best to manage connectivity to optimize resistance gene deployment while avoiding risks to the useful life of resistance genes. [Formula: see text] Copyright

Epidemic Network Analysis for Mitigation of Invasive Pathogens in Seed Systems: Potato in Ecuador

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 approach for evaluating the epidemiological role of nodes in seed networks, and apply it to a regional potato farmer consortium (Consorcio de Productores de Papa [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 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. However, women had a smaller amount of the market share for seed tubers and ware potato. Understanding seed system networks provides input for scenario analyses to evaluate potential system improvements. [Formula: see text] Copyright

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

Seed systems are critical for deployment of improved varieties, but also serve as major conduits for the spread of seed-borne pathogens. We evaluated the structure of an informal sweetpotato seed system for its vulnerability to the spread of epidemics, and its utility for disseminating improved varieties. During the 2014 growing season, vine sellers were surveyed weekly in the Gulu Region of Northern Uganda. Our analysis draws on tools from network theory to evaluate the potential for epidemic spread in this region. Using empirical seed transaction data and estimated spatial spread, we constructed a network of seed and pathogen movement. We modeled the introduction of a pathogen, and evaluated the influence of both epidemic starting point and quarantine treatments on epidemic progress. Quarantine of 30 out of 99 villages reduced epidemic progress by up to 66%, when compared to the control (no quarantine), over 20 time steps. The starting position in the network was critical for epidemic progress and final epidemic outcomes, and influenced the percent control conferred by quarantine treatments. Considering equal likelihood of any node being an introduction point for a new epidemic, villages of particular utility for disease monitoring were identified. Sensitivity analysis identified important parameters and priorities for future data collection. The efficacy of node degree, closeness, and eigenvector centrality was similar for selecting quarantine locations, while betweenness had more limited utility. This analysis framework can be applied to provide recommendations for a wide variety of seed systems.Seed systems are critical for deployment of improved varieties, and serve as major conduits for the spread of seed-borne pathogens. Vegetatively propagated crops in low-income countries are particularly vulnerable to seed degeneration, where yield is lowered through successive cycles of propagation because of pathogen accumulation. We evaluated the structure of an informal sweetpotato seed system for its vulnerability to the spread of epidemics, and its utility for disseminating improved varieties. During the 2014 growing season (April-Oct), vine sellers were surveyed weekly in the Gulu Region of Northern Uganda. Our analysis draws on tools from network theory to evaluate the potential for epidemic spread in this region. Utilizing empirical 2014 seed transaction data and estimated spatial spread, we constructed a seed transaction network, which was used to simulate the introduction of a pathogen, and evaluated the influence of both epidemic starting point and quarantine treatments on epidemic progress. Results indicate that the starting position in the network is critical for epidemic progress and final epidemic outcomes. Quarantine of 30 villages lowered epidemic progress up to 65.7%, when compared to the control (no quarantine), over 20 timesteps in 500 realizations. The percent control conferred by quarantine treatments was also influenced by the epidemic starting point. Considering equal likelihood of any node being an introduction point for a new epidemic, villages of particular utility for disease monitoring were also identified. Sensitivity analysis identified important parameters and priorities for future data collection. We compared the utility of node degree, betweenness, closeness, and eigenvector centrality for selecting quarantine locations, finding that betweenness had more limited utility. This analysis pipeline can be applied to provide recommendations for a wide variety of seed systems.The structure of seed system networks provides important information about epidemic risk within the network. We evaluated the structure of a sweetpotato seed system in Northern Uganda in terms of its utility for distributing improved varieties and its vulnerability to the spread of potential seed-borne pathogens. Sweetpotato sellers were surveyed in the Gulu Region of Northern Uganda. Weekly vine sales transactions were tracked through the growing season (April-October) creating a robust dataset of planting material sales over time, including price, village sold to, volume, and information about the buyer and seller. From this dataset of known transactions and the distance between villages, a network of vine movement was constructed. In silico simulations of the introduction of a novel virus into the systems indicated the potential for rapid spread. Through simulation of multiple epidemic starting points, nodes of particular importance to disease sampling and mitigation were identified. This method can serve as an example, with potential to be used across a wide variety of seed systems.

Modeling Epidemics in Seed Systems: Sweetpotato in Northern Uganda

Seed systems are critical for deployment of improved varieties, but also serve as major conduits for the spread of seed-borne pathogens. We evaluated the structure of an informal sweetpotato seed system for its vulnerability to the spread of epidemics, and its utility for disseminating improved varieties. During the 2014 growing season, vine sellers were surveyed weekly in the Gulu Region of Northern Uganda. Our analysis draws on tools from network theory to evaluate the potential for epidemic spread in this region. Using empirical seed transaction data and estimated spatial spread, we constructed a network of seed and pathogen movement. We modeled the introduction of a pathogen, and evaluated the influence of both epidemic starting point and quarantine treatments on epidemic progress. Quarantine of 30 out of 99 villages reduced epidemic progress by up to 66%, when compared to the control (no quarantine), over 20 time steps. The starting position in the network was critical for epidemic progress and final epidemic outcomes, and influenced the percent control conferred by quarantine treatments. Considering equal likelihood of any node being an introduction point for a new epidemic, villages of particular utility for disease monitoring were identified. Sensitivity analysis identified important parameters and priorities for future data collection. The efficacy of node degree, closeness, and eigenvector centrality was similar for selecting quarantine locations, while betweenness had more limited utility. This analysis framework can be applied to provide recommendations for a wide variety of seed systems.Seed systems are critical for deployment of improved varieties, and serve as major conduits for the spread of seed-borne pathogens. Vegetatively propagated crops in low-income countries are particularly vulnerable to seed degeneration, where yield is lowered through successive cycles of propagation because of pathogen accumulation. We evaluated the structure of an informal sweetpotato seed system for its vulnerability to the spread of epidemics, and its utility for disseminating improved varieties. During the 2014 growing season (April-Oct), vine sellers were surveyed weekly in the Gulu Region of Northern Uganda. Our analysis draws on tools from network theory to evaluate the potential for epidemic spread in this region. Utilizing empirical 2014 seed transaction data and estimated spatial spread, we constructed a seed transaction network, which was used to simulate the introduction of a pathogen, and evaluated the influence of both epidemic starting point and quarantine treatments on epidemic progress. Results indicate that the starting position in the network is critical for epidemic progress and final epidemic outcomes. Quarantine of 30 villages lowered epidemic progress up to 65.7%, when compared to the control (no quarantine), over 20 timesteps in 500 realizations. The percent control conferred by quarantine treatments was also influenced by the epidemic starting point. Considering equal likelihood of any node being an introduction point for a new epidemic, villages of particular utility for disease monitoring were also identified. Sensitivity analysis identified important parameters and priorities for future data collection. We compared the utility of node degree, betweenness, closeness, and eigenvector centrality for selecting quarantine locations, finding that betweenness had more limited utility. This analysis pipeline can be applied to provide recommendations for a wide variety of seed systems.The structure of seed system networks provides important information about epidemic risk within the network. We evaluated the structure of a sweetpotato seed system in Northern Uganda in terms of its utility for distributing improved varieties and its vulnerability to the spread of potential seed-borne pathogens. Sweetpotato sellers were surveyed in the Gulu Region of Northern Uganda. Weekly vine sales transactions were tracked through the growing season (April-October) creating a robust dataset of planting material sales over time, including price, village sold to, volume, and information about the buyer and seller. From this dataset of known transactions and the distance between villages, a network of vine movement was constructed. In silico simulations of the introduction of a novel virus into the systems indicated the potential for rapid spread. Through simulation of multiple epidemic starting points, nodes of particular importance to disease sampling and mitigation were identified. This method can serve as an example, with potential to be used across a wide variety of seed systems.

Network Analysis: A Systems Framework to Address Grand Challenges in Plant Pathology

Plant pathology must address a number of challenges, most of which are characterized by complexity. Network analysis offers useful tools for addressing complex systems and an opportunity for synthesis within plant pathology and between it and relevant disciplines such as in the social sciences. We discuss applications of network analysis, which ultimately may be integrated together into more synthetic analyses of how to optimize plant disease management systems. The analysis of microbiome networks and tripartite phytobiome networks of host-vector-pathogen interactions offers promise for identifying biocontrol strategies and anticipating disease emergence. Linking epidemic network analysis with social network analysis will support strategies for sustainable agricultural development and for scaling up solutions for disease management. Statistical tools for evaluating networks, such as Bayesian network analysis and exponential random graph models, have been underused in plant pathology and are promising for informing strategies. We conclude with research priorities for network analysis applications in plant pathology.

Pathogen mitigation in an Ecuadorian potato seed system: Insights from network analysis

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.The structure of seed systems has important implications for how likely they are to effectively supply high quality seed to communities of farmers. We evaluated seed system networks defined by a regional potato farmer consortium (CONPAPA) in Tungurahua, Ecuador. Networks were structured around farmer seed and potato transactions and their sources of information about pest and disease management. We performed a scenario analysis of disease spread that takes into account interacting biophysical, socioeconomic and informational elements. CONPAPA provides training, seed improvement and potato processing and marketing for its members. The high centrality of CONPAPA in the network means that disease management interventions, such as training, monitoring and variety dissemination should target CONPAPA staff and processing facilities. The market in Ambato, the largest nearby town, was the next most useful place to monitor. Farmers reported receiving advice about disease and pest management through trusted CONPAPA technical staff. Local agricultural stores were also reported as providing advice to many farmers, but were viewed by farmers as significantly less reliable. Training of store owners could provide one way to improve outcomes in this seed system. Farmer access to information (number and quality of sources) was equal for both genders. Female farmers had a smaller than expected amount of the market share, however. In CONPAPA there is 47% adoption of improved seed, much higher than the 2% rate reported for Ecuador in general. This is probably improving yields significantly for small farmers in the consortium. Agricultural seed systems and network analyses provide one window into a variety of global change phenomena encompassing environmental and societal concerns.

Analyzing Key Nodes and Epidemic Risk in Seed Networks: Sweetpotato in Northern Uganda

Seed systems are critical for deployment of improved varieties, but also serve as major conduits for the spread of seed-borne pathogens. We evaluated the structure of an informal sweetpotato seed system for its vulnerability to the spread of epidemics, and its utility for disseminating improved varieties. During the 2014 growing season, vine sellers were surveyed weekly in the Gulu Region of Northern Uganda. Our analysis draws on tools from network theory to evaluate the potential for epidemic spread in this region. Using empirical seed transaction data and estimated spatial spread, we constructed a network of seed and pathogen movement. We modeled the introduction of a pathogen, and evaluated the influence of both epidemic starting point and quarantine treatments on epidemic progress. Quarantine of 30 out of 99 villages reduced epidemic progress by up to 66%, when compared to the control (no quarantine), over 20 time steps. The starting position in the network was critical for epidemic progress and final epidemic outcomes, and influenced the percent control conferred by quarantine treatments. Considering equal likelihood of any node being an introduction point for a new epidemic, villages of particular utility for disease monitoring were identified. Sensitivity analysis identified important parameters and priorities for future data collection. The efficacy of node degree, closeness, and eigenvector centrality was similar for selecting quarantine locations, while betweenness had more limited utility. This analysis framework can be applied to provide recommendations for a wide variety of seed systems.Seed systems are critical for deployment of improved varieties, and serve as major conduits for the spread of seed-borne pathogens. Vegetatively propagated crops in low-income countries are particularly vulnerable to seed degeneration, where yield is lowered through successive cycles of propagation because of pathogen accumulation. We evaluated the structure of an informal sweetpotato seed system for its vulnerability to the spread of epidemics, and its utility for disseminating improved varieties. During the 2014 growing season (April-Oct), vine sellers were surveyed weekly in the Gulu Region of Northern Uganda. Our analysis draws on tools from network theory to evaluate the potential for epidemic spread in this region. Utilizing empirical 2014 seed transaction data and estimated spatial spread, we constructed a seed transaction network, which was used to simulate the introduction of a pathogen, and evaluated the influence of both epidemic starting point and quarantine treatments on epidemic progress. Results indicate that the starting position in the network is critical for epidemic progress and final epidemic outcomes. Quarantine of 30 villages lowered epidemic progress up to 65.7%, when compared to the control (no quarantine), over 20 timesteps in 500 realizations. The percent control conferred by quarantine treatments was also influenced by the epidemic starting point. Considering equal likelihood of any node being an introduction point for a new epidemic, villages of particular utility for disease monitoring were also identified. Sensitivity analysis identified important parameters and priorities for future data collection. We compared the utility of node degree, betweenness, closeness, and eigenvector centrality for selecting quarantine locations, finding that betweenness had more limited utility. This analysis pipeline can be applied to provide recommendations for a wide variety of seed systems.The structure of seed system networks provides important information about epidemic risk within the network. We evaluated the structure of a sweetpotato seed system in Northern Uganda in terms of its utility for distributing improved varieties and its vulnerability to the spread of potential seed-borne pathogens. Sweetpotato sellers were surveyed in the Gulu Region of Northern Uganda. Weekly vine sales transactions were tracked through the growing season (April-October) creating a robust dataset of planting material sales over time, including price, village sold to, volume, and information about the buyer and seller. From this dataset of known transactions and the distance between villages, a network of vine movement was constructed. In silico simulations of the introduction of a novel virus into the systems indicated the potential for rapid spread. Through simulation of multiple epidemic starting points, nodes of particular importance to disease sampling and mitigation were identified. This method can serve as an example, with potential to be used across a wide variety of seed systems.