A pest risk analysis (PRA) is the foundation for fact-based and proportionate phytosanitary regulations instituted by a country.

Is seed a pest risk?

Is seed a pest risk?

A pest risk analysis (PRA) is the foundation for fact-based and proportionate phytosanitary regulations instituted by a country. However, in practice PRAs are difficult to do. Many countries do not have the resources to perform all the PRAs needed – neither in a reasonable period of time nor with the thoroughness they require. Often they are not specific to seed for sowing. PRAs for seed for sowing must take into consideration that some pests may not be transmitted from the seed to the plant grown from that seed.

The rationale for phytosanitary measures

The three stage process of a pest risk analysis (ISPM 2 and ISPM 11) provides a basis for determining the potential of seed being a pest risk.

Identification of an organism and pathway: Even though certain pests may be associated with a given species of plant, far fewer are actually directly associated with the seed of the species in question. The PRA should determine if the seed is a pathway for the introduction and spread of regulated pests and may lead to establishment of regulated pests in the PRA area.

Pest risk assessment, i.e. assessment of introduction, establishment and spread, and assessment of economic impacts: Numerous research papers on plant diseases are published every year. Many note that the pest in question “can or has been found on seeds”. How relevant are such reports? The presence of a pest on or in the seed does not necessarily mean that it can be transmitted from the seed into the resulting plant.

Pest risk management, i.e. identification of phytosanitary measures that (alone or in combination) reduce the risk to an acceptable level: The seed business today uses many recognized risk reduction and prevention measures for seed pests of concern, such as seed certification schemes, resistant varieties, seed testing and seed treatments.

Pest Risk Analysis

National plant protection and quarantine authorities have the mandate for protecting the resources of their countries from invasive pests entering from outside their borders.

National plant protection and quarantine authorities have the mandate for protecting the resources of their countries from invasive pests entering from outside their borders. The import of seed is one among other potential carriers of unwanted pests such as people, commodities and conveyances. While prohibiting the import of seed may be an effective method of excluding foreign pests, it runs the risk of being perceived as a trade barrier unless justified by a risk analysis.

The term Pest Risk Analysis was invented by the phytosanitary community approximately ten years ago to distinguish the type of risk analysis done to support official decision making for the application of phytosanitary measures, and grew into prominence with the WTO Agreement on the Application of Sanitary and Phytosanitary measures (the SPS Agreement). A fundamental tenet of the SPS Agreement is that measures for the protection of plant, animal or human health or life are based on international standards or an assessment of risk taking into account scientific principles and evidence. The outcome is the identification of exotic pests and the implementation of quarantine security measures to guard against their accidental importation.

But the process of determining which security measures are appropriate and cost effective is a complex and, sometimes, subjective matter. One of the prime functions of risk analysis as applied to trade is to put this process on an objective basis. FAO in its publication on Guidelines for Pest Risk Analysis (ISPM Publication 2, Feb 1996; www.ippc.int) has elaborated the general requirements for a pest risk analysis. It consists of three stages: initiating the process for analysing risk, assessing pest risk, and managing risk. It is aimed at helping governments discipline their judgement on phytosanitary measures by placing emphasis on scientific evidence and principles in its analysis of risk in the international movement of seed. ISF commissioned a PRA on Erwinia stewartii in Maize.

Relevant Links

International Plant Protection Convention (IPPC)

ISF Regulated Pest List Initiative

ISF Regulated Pest List Initiative

Seed moved internationally, either for research or trade, are subject to phytosanitary regulations to minimise the risk of introducing or spreading pests worldwide. However, in some instances the phytosanitary measures imposed are unnecessary as seed is not a pathway for the entry, establishment or spread of the pest in question. After scanning national phytosanitary regulations from around the world, ISF has listed the regulated pathogenic organisms (bacteria, fungi, insects, nematodes, oomycetes, phytoplasma, viruses and viroids) for a number of seed species. Using their knowledge and experience, company seed and field pathologists provided an expert interpretation of scientific publications on whether seed was a means for the entry of each pest in the list and the conditions for its establishment.

Scientific articles published in refereed journals or scientific websites of the International Committee on Taxonomy of Viruses (ICTV), the Nematode-Plant Expert Information System (Nemaplex), the International Mycological Association (mycobank) and others were consulted. These ISF Pest Lists have been assembled in the form of a database. For those pests for which seed is a pathway or where the pathway is not yet conclusively proven, the database provides information on detection and risk mitigation. The database is a work in progress.

Technical documents

There are numerous articles on plant diseases published in which the authors note that the pest in question was found on seed. Often the relevance of such publications is questionable. The presence of a plant pathogen on seed does not necessarily mean that it transmits a disease or that seed is a pathway for establishment of the pathogen. The conclusion drawn of a pest being seed borne or seed transmitted may be based on experimental evidence, limited observations, or in some cases, simply suggestive statements. Many pests that are not seed transmitted or for which seed is not a pathway for establishment are, nevertheless, regulated.

Seed companies have to meet these requirements, even when they are not technically justified, in order to move seed. To meet regulatory requirements for pests where seed has not been proven to be a pathway, the seed industry has developed the following technical documents.


The database is a “living document” subject to periodic review and updates based on feedback from users and changes in national phytosanitary regulations for seed. Your feedback is invited. If you think some of the information related to a pest is incorrect or incomplete, use the means provided in the database (“Report an error”) to inform the ISF Secretariat. It will be used to update the database, if necessary.


ISF and its members have done their best to provide information that is up-to-date. The information is based on refereed articles and journals. ISF and its members cannot accept any liability for the use of this information.