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Seeds are the foundation for crop production and seed health is related to food production in many ways. Healthy seeds, free from known seed transmitted pathogens, are a prerequisite for sustainable food production.
Seeds may present a pest risk. They are, therefore, routinely tested to prevent or control plant pests and pathogens that may affect seed quality, seed movement, and their introduction into new territories. A seed health test is also frequently a phytosanitary requirement imposed by national plant protection authorities before allowing seed to enter their territory.
THE INTERNATIONAL SEED HEALTH INITIATIVE (ISHI)
The International Seed Health Initiative (ISHI) for Vegetable Crops was initiated in 1993 to provide a forum for exchanging information, sharing expertise on seed health testing and facilitating the development of new seed health tests. ISHI brings together seed companies, public sector institutions, and private laboratories to develop seed health tests for economically important pathogens associated with seed. 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 healthy seed to customers by developing and validating methods for seed health testing that are internationally recognized as reference methods and accepted as industry standards.
Through the use of seed health test methods and our expertise, we 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 main 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. These direct tests demonstrate the presence of a pathogen on and/or in the seed.
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. However, indirect tests used for pathogen detection do not yield any information about pathogen viability and are not sufficient to prove pathogenicity.
The 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 ISHI Technical resources – ISF Viewpoint on Indirect Seed Health Tests. Because indirect tests can 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 has identified performance criteria for the validation of pre-screen PCR methods to ensure their robustness and reproducibility, see ISHI Technical Resources – Real-Time PCR pre-screening in seed health methods.
The HTS technologies are relatively new and have potential advantages but also limitations for use in seed health testing. Similarly to ELISA and PCR, 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 in combination with a confirmatory test for positive results, see ISHI Technical Resources – 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 ISHI Technical Resources – Guidelines on Seed Health Testing in the Vegetable Seed Industry.