The Need and a Vision for a Diagnostic Assay Validation Network
Authors: Cardwell Kitty F. , Harmon Carrie L. , Luster Douglas G. , Stack James P. , Hyten Aimee M. , Sharma Poonam , Nakhla Mark K. 
Published: February 2023

Plant biosecurity depends heavily on early detection of biological pest and disease threats and accurate diagnosis of causal agents. The information from these activities is disseminated and communicated with decision makers to promote effective mitigation. In the United States, most land-grant university, state, and private diagnostic and expert pest identifier labs are successfully networked via the U.S. Department of Agriculture Animal Plant Health Inspection Service, Plant Protection and Quarantine (USDA APHIS PPQ; https://www.aphis.usda.gov/ ), the National Plant Diagnostic Network (NPDN; https://www.npdn.org ), and the National Clean Plant Network (NCPN; https://www.nationalcleanplantnetwork.org/ ). These organizations provide access to training, shared protocols, and standardized communications. For example, the NPDN has secure communications tools that network leadership built into its IT infrastructure and deploys a formal communications process and protocol for regulatory and high-risk samples. Additionally, the diagnostic networks adopt protocols from regulatory organizations such as the USDA-APHIS, European and Mediterranean Plant Protection Organization (EPPO), North American Plant Protection Organization (NAPPO), and other international and national plant protection organizations (NPPOs). However, plant health diagnosticians also need access to validated protocols for endemic and nonregulated organisms. Although there is strong networking of diagnostic laboratories, plant disease diagnostic assay development and validation are siloed, representing a critical gap in our biosecurity infrastructure, especially for new or emerging pathogens. Most assays are developed in independent research labs and then chosen independently by the end-use laboratory. Assay developers, those who provide reference materials, labs that can provide ring testing for validation, and assay end users could be connected and integrated for more streamlined operations. Terminology and validation protocols need to be standardized within the United States and harmonized with our trade partners to ensure understanding. The ideal would be availability of standard, taxon-specific validation protocols, essential reference materials, and appropriate control materials for use to quickly develop and deploy assays in emergencies, as well as for day-to-day testing. This perspective article provides a summary of principles of assay validation, fitness-for-purpose concepts, and the need for continuous evaluation of assay performances. We describe the existing capacity and resources needed to efficiently develop, validate, and use diagnostic tests, as well as the inefficiencies and resource shortfalls currently faced. We propose development of a Diagnostic Assay Validation Network (DAVN) system to coordinate resources at the national level and harmonize with our partners at the international level. Here, we outline a project to set up the DAVN with the objectives of standardizing terminology and statistics and facilitating location of reference materials used in diagnostic assay development and validation via a portal of tools designed by and for the plant disease research and extension community. Although many of the concepts are also relevant to insects and other pests, the focus of this article is primarily plant pathogens.

[Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .