DC McGEE

Seed Science Center and Department of Plant Pathology, Iowa State University, Ames, IA 50011, USA

Backgound and objectives
The past 20 years have shown major increases in the amount of commercial seed lots that cross international boundaries. In addition, international research centres and multinational seed companies distribute massive numbers of germplasm and breeding line samples throughout the world annually. The large volume of seed now moving internationally, together with a proliferation of new quarantine regulations, has severely tested the ability of the current international phytosanitary certification system to prevent the spread of economically important seedborne pathogens without posing unnecessary barriers to worldwide movement of seeds. Plant pathologists can play a major role in resolving this seed health problem.

Since its emergence as a subdiscipline of plant pathology from seed quality testing in the early 20th century, seed pathology research has focused on detection of seedborne microorganisms and development of seed health testing methods. These priorities must be expanded in order to address the economic significance of seedborne pathogens as they relate to quality of seeds and to transmissibility of pathogens by seeds. This symposium emphasizes three specific areas of research in seed pathology that can contribute to improving the global seed health system.

Results and discussion
There are very few inoculum thresholds for seedborne pathogens that are based on sound epidemiological research requiring seed health assays that are specific, accurate, reproducible, practical, and have a degree of sensitivity that relates to the application of the assay results. Experiments must also be carried out to correlate the incidence of seed infection with plant infection in the field. Research on this topic is both complex and expensive, but is absolutely fundamental to realistic and effective management of seed transmission of plant pathogens.

Molecular and serological seed health testing methods have revolutionized plant disease diagnostics. In the area of seed pathology, they offer the opportunity for development of rapid, sensitive and specific seed health assays. They also have opened up the area of detection of seedborne bacteria and viruses, that have been difficult to test for with traditional methods.

Lack of access to scientific information is a major contributory factor in establishing unnecessary phytosanitary regulations. An extensive world literature on seedborne diseases exists that could be used to determine seedborne pathogens that constitute economic risk. However, it remains largely untapped, due to a lack of systematic organization of the information and to difficulties in accessing hard copy reference sources, particularly in developing countries. Recent advances in the electronic media are now being exploited to disseminate seedborne disease data efficiently and economically throughout the world.

References
1. McGee DC, 1995. Annual Review of Phytopathology 33, 443-466.
2. McGee DC (ed.), 1997. APS Press, St Paul, Minnesota.