US: Interpreting post-harvest test results

Seed certification is a quality control program that consists of a number of components intended to ensure that specified quality standards are met. One of the more important of these components is post-harvest testing. Post-harvest testing may consist of an off-season grow-out in the field or greenhouse, laboratory testing, or some combination of these. The vast majority of Idaho seed lots are post-harvest tested in a winter grow-out conducted in Waialua, Hawaii. This grow-out consists of a visual assessment of grower-submitted samples for  potato leaf roll virus and a laboratory test of harvested leaves for potato virus Y (PVY). While the process of post-harvest testing and the reporting of results is relatively straightforward, we do occasionally receive questions about why reported post-harvest test results differ from what is observed in the field the following season. This has been a particular issue with PVY levels observed in some seed lots. Why does this occur? More