International Seed Health Initiative for Vegetable Crops (ISHI-Veg)
The International Seed Health Initiative for Vegetables Crops (ISHI-Veg) was set up in 1993. Its members account for 70-75% of vegetable seed that is traded internationally. ISHI-Veg bring together seed companies, public sector institutions and private laboratories to develop detection methods for economically important seed-borne pathogens of vegetable crops.
ISHI-Veg 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).
ISHI-Veg methods have been developed using the collective experience and expertise of its members. Developing a seed health testing method is complex and requires a consideration of disease dynamics. The epidemiology of a disease depends upon the pathogen infection levels within the seed, the climate in which the seed is grown, and the interactions of the host, pathogen and the environment.
Comprehensive studies that elucidate all these aspects are often not possible to find, as data may be scattered and sometimes inconclusive. Seed pathologists within ISHI-Veg bring together the necessary experience and data in developing a test method. In addition ISHI-Veg makes recommendations on sub-sample and sample sizes for each method.
Seed Health Testing
These seed health test methods are a tool for seed-borne disease risk management, which is itself a part of a company’s seed-borne disease control program. Plant disease control is achieved by reducing the progress of the disease and keeping disease development below a consequential level. ISHI-Veg methods are a reference for the vegetable seed industry, which adopted a position (Guidelines for the Use of Seed Health Methods by the Vegetable Seed Industry) concerning their use in 2010.
Interpretation of the seed health test results
The seed industry recognizes that even when tests are carried out correctly according to the protocol, differences can exist due to the expression or condition of the pathogen. Tests can show identical results in cases where the pathogen is viable but a deviating result if the pathogen is dead or inactivated.
Many countries active in seed health testing make use of modern laboratory techniques. A PCR may be easier to implement by a developing country than a traditional direct method that requires skilled pathologists. Indirect tests (e.g. serological techniques and DNA/RNA based techniques) will detect both dead/non-infectious and viable/infectious pathogens in contrast to direct tests (grow-outs and bioassays) that give final proof of infestation by a viable pathogen.
Diagnostic methods for seed health testing should have the right balance between preventing infected seed lots from being sold (as a consequence of a false negative test result) and preventing unjustified measures such as discarding seed lots (as a consequence of a false positive test result). There are, however, considerations in using such indirect techniques and ISF has taken a position on their use (ISF Viewpoint on Indirect Seed Health Tests).