Seed testing plays a pivotal role in helping meet market demand for clean and healthy seed, both domestically and internationally. Our test methods are used to provide phytosanitary information for the international trade of seed and quality information on seed lots for domestic sales.
From an international perspective, there is now an increased emphasis on phytosanitary requirements for the international movement of seed. Each country has a different, unique set of phytosanitary requirements — some of which might not be scientifically justified — and this creates a challenge for companies that frequently import and export seed. Dr. Ric Dunkle from the American Seed Trade Association has previously given an excellent update on this ever-changing topic.
For this article, the focus is on current and future seed health testing and why this is important to the seed trade in the United States. Phytosanitary requirements for international seed trade aside, the U.S. domestic seed market has very high quality standards that encompass many factors. Seed health is one of those factors that has progressively become more important with each year that passes and each new seed-borne disease that rears up. The increasing emphasis on seed health has impacted not only the amount of seed health testing that is done by companies, but also has reached into production practices for commercial seed, stock seed, foundation seed and even breeder seed.
In evaluating their seed production systems, companies are looking at the environment, the crop and the pathogens of concern. Best production practices include, but are not limited to, crop rotation, scouting, using resistant varieties and seed testing. It is well documented that seed can be the primary inoculum source for a disease in the field.
There are two main seed testing approaches for target pathogens, traditional and molecular. Traditional methods have been reliable and generally show the physical presence of the pathogen either by its characteristic structures or through pathogenicity and are thus referred to as direct methods. However, they can lack sensitivity, the ability to detect low levels of the pathogen in a seed sample. Molecular methods are more sensitive but are indirect methods, meaning they do not generate a biological isolate or prove pathogenicity. For traditional plant pathologists, this can be a concern. An example of a molecular method is PCR testing.
All of the current seed health testing methods, whether traditional or molecular, have pros and cons, but the direction of testing procedures in the future is going toward more sensitive and robust testing methods, reducing the time for testing as well as the cost per test without compromising the accuracy of the result. This remains our mission for seed health professionals for the future.