The International Seed Health Initiative for Vegetable Crops (ISHI-Veg) came into being in 1993 to provide a forum for exchanging information, sharing expertise on seed health testing and facilitating the development of new seed health tests. Today, our members account for 70-75% of vegetable seed that is traded internationally.
OUR VISION AND MISSION
We aim to secure the delivery of sufficiently healthy seed to customers by developing methods for seed health testing that are internationally recognized as reference methods and accepted as industry standards.
Through the use of these methods and our expertise we strive to assist seed companies in their risk management, advocate for the seed industry on seed health related issues and facilitate the international movement of seeds.
OUR SEED HEALTH TESTS
A seed health test has historically consisted of three primary steps: i) isolating the pathogen from seeds, ii) detecting and identifying the pathogen, and iii) confirming the viability of the isolate and its pathogenicity by inoculating it into assay plants. In such direct tests, the presence of a pathogen on and/or in the seed is demonstrated.
In recent years direct tests have been complemented with faster, simpler and relatively inexpensive techniques, such as ELISA and PCR. They provide an indirect means of signalling the presence of the pathogen by identifying the presence of pathogen-specific proteins or nucleic acids in/on seed. Indirect tests used for pathogen detection do not yield any information about pathogen viability and are not sufficient to prove pathogenicity.
ISF is of the view that a negative result in an indirect test requires no additional testing to confirm that the seed lot in question is healthy, see ISF Viewpoint on Indirect Seed Health Tests. Because indirect tests detect proteins and nucleic acids from dead and inactivated pathogens that are unable to transmit disease, a positive result only indicates that the seed lot is suspected of being infected with the target pathogen. A confirmatory test that shows the target pathogen to be viable and pathogenic must follow.
The indirect test is, therefore, used as a pre-screen in seed health testing. As the use of nucleic-acid based techniques, such as PCR and High Throughput Sequencing (HTS) or Next Generation Sequencing, has increased compared to other indirect techniques in seed health testing in recent years, ISHI-Veg has identified performance criteria for validation of pre-screen PCR methods to ensure their robustness and reproducibility, see Real-Time PCR pre-screening in seed health methods.
HTS technologies are relatively new and have potential advantages but also limitations for use in seed health testing. To ensure a correct assessment of the health status of a seed lot and avoid unwarranted phytosanitary regulations based solely on HTS results, these technologies should be used as a pre-screen and in combination with other assays, including a direct test. See High Throughput Sequencing in Seed Health Testing.
Our methods are a reference for the vegetable seed industry, which adopted a position concerning the use of ISHI-Veg seed health methods, see Guidelines for the Use of Seed Health Methods by the Vegetable Seed Industry.
To ensure accurate and reliable results ISHI-Veg has described best practices for PCR, ELISA and dilution-plating assays used in routine seed health testing. Best practices for other assays are in preparation. They are intended to provide general guidance to labs developing and using seed health tests, and to ensure accurate and reliable results.
Best Practices for PCR Assays in Seed Health Tests (2019)
Best Practices for Dilution Plating Assays in Seed Health Tests (2020)
Best Practices for ELISA Assays in Seed Health Tests (2019)
Best Practices for Blotter Assays in Seed Health Tests (2018)
Best Practices for Sweat Box Assays in Seed Health Tests (2018)