Seed health testing is a tool for seed-borne disease risk management and is a part of the entire seed-borne disease control program. This manual provides descriptions of seed health testing methods that are considered by ISHI-Veg to be the reference for the vegetable seed industry. The methods are the basis for the position adopted by the vegetable seed sector in May 2006 titled “Guidelines for the Use of Seed Health Methods by the Vegetable Seed Industry”.
The described methods have a well-established track record in the seed industry and are recognized as reference methods by seed pathologists from testing laboratories of inspection services, private testing labs and the vegetable seed industry. In addition, some ISHI-Veg methods have been accepted as ISTA Rules and as Standards by the USDA-APHIS National Seed Health System (NSHS).
Developing a seed health testing method is complex and requires a consideration of the disease dynamics. The epidemiology of a disease, a change in the disease in time and space, depends on the infection level in the seed, the climatic zone where the seed is grown and the effect of such zones on infection rates. Comprehensive studies that elucidate all these aspects are often not possible to find, as data are usually scattered and inconclusive. The collective experience within ISHI-Veg allows for test methods to be developed that take into account the above-mentioned factors through recommendations on sub sample and sample sizes. Plant disease control is achieved by reducing the progress of the disease and keeping disease development below an acceptable level.
The method descriptions serve as a reference for achieving uniformity in seed health testing. Although these protocols have been reviewed and tested over time by the industry, the results of the tests may vary because standardized reference materials (controls) are not readily available for seed health testing. Also, similar results can be obtained with alternative methods (see below). Consequently, when possible, an indication on how to verify test performance is provided in the method by indicating a “sensitivity reference”. It is also recommended that laboratories interested in using these methods participate in proficiency testing programs.
For each crop/pathogen combination the key elements of the method are given. The descriptions are aimed to be sufficiently clear to laboratory staff with ample experience in working with plant pathogens. The principles of Good Laboratory Practice (http://ec.europa.eu/enterprise/pharmaceuticals/eudralex/vol-7/a/7ag4a.pdf) should be followed at all times.
It is strongly recommended that a sample of a seed lot with a known infestation level be included as a positive check in every set of samples that is tested at a time.
Several methods contain multiple steps that can and should be verified separately with materials other than infested seeds. A numbering system is used for each of these steps in the method descriptions.
As mentioned above, similar results can be obtained using different test methods. When alternative methods are found by ISHI-Veg to be equivalent in their results, they may be included in the manual. Accepted alternatives for certain elements of the test method are indicated within the description. For example, the method for Alternaria radicina of carrot contains three fully separate methods and each was found to be acceptable as a reference method.
It is important to note that serological techniques and DNA/RNA based techniques will detect both dead/non-infectious and viable/infectious pathogens. In contrast, grow-outs and bioassays give final proof of infestation by a viable pathogen. Therefore, ELISA and bioassay for viruses on tomato seeds are not equivalent. The ELISA technique is considered an optional pre-screening method for the bioassay and the test can be terminated when a negative ELISA result is obtained. If a positive ELISA result is obtained then the bioassay must be completed.
The contribution of past and present members of ISHI-Veg is acknowledged. A special thanks is given to Kees van Ettekoven (Naktuinbouw, the Netherlands) who first compiled the information in the manual.
ISF cannot guarantee that the results obtained by laboratories which follow the protocol from this manual are accurate and representative as many factors (e.g. personnel skills, lab conditions, quality of reagents, sampling methods etc.) can influence the results. Consequently, ISF will not accept any liability with respect to the use of the methods in this manual in case of litigation.
NOTE: Methods presented in this manual may be updated at any time. It is the responsibility of the user to see that the most recent version of a method is being applied.
Contact the ISF Secretariat for more information
Announcement
ISF Secretariat - Chemin du Reposoir 7 - 1260 Nyon Switzerland
tel +41 22 365 44 20 - fax +41 22 365 44 21 - isf@worldseed.org
ISF Secretariat
Chemin du Reposoir 7
1260 Nyon Switzerland
tel +41 22 365 44 20
isf@worldseed.org
