|CHOUDHURY, ROBIN - University Of Florida|
|GARRETT, KAREN - University Of Florida|
|SUBBARAO, KRISHNA - University Of California|
|MCROBERTS, NEIL - University Of California|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2017
Publication Date: 9/19/2017
Citation: Choudhury, R.A., Garrett, K.A., Klosterman, S.J., Subbarao, K.V., Mcroberts, N. 2017. A framework for optimizing phytosanitary thresholds in seed systems. Phytopathology. 107(10):1219-1228. https://doi.org/10.1094/PHYTO-04-17-0131-FI.
Interpretive Summary: Reduction in the amounts of plant pathogens that are imported on seeds, either internationally or between states in the U.S., is an important goal. Pathogens that are already endemic to the U.S. do not have the same regulatory standards, and thus are permitted to enter without scrutiny on seeds, even though there are different strains of the pathogens carried on these seeds. This work examines means to assess thresholds of the levels of the pathogen that are acceptable, and the costs associated with such thresholds, and their implementation. Pathogen reductions on seed by established parameters are anticipated to result in lower economic losses.
Technical Abstract: Seedborne pathogens and pests limit production in many agricultural systems. Quarantine programs help prevent the introduction of exotic pathogens into a country, but few regulations directly apply to reducing the reintroduction and spread of endemic pathogens. Use of phytosanitary thresholds helps limit the movement of pathogen inoculum through seed, but the costs associated with rejected seed lots can be prohibitive for voluntary implementation of phytosanitary thresholds. In this paper, we outline a framework to optimize thresholds for seedborne pathogens, balancing the cost of rejected seed lots and benefit of reduced inoculum levels. The method requires relatively small amounts of data, and the accuracy and robustness of the analysis improves over time as data accumulate from seed testing. We demonstrate the method first and illustrate it with a case study of seedborne oospores of Peronospora effusa, the causal agent of spinach downy mildew. A seed lot threshold of 0.23 oospores per seed could reduce the overall number of oospores entering the production system by 90% while removing 8% of seed lots destined for distribution. Alternative mitigation strategies may result in lower economic losses to seed producers, but have uncertain efficacy. We discuss future challenges and prospects for implementing this approach.