Testing Q&As


Testing Q&As

What tests are available at the ISU Seed Lab?
The Iowa State University Seed Laboratory conducts many types of tests on more than 300 species of seed. A partial list of tests appears on the Testing Methods page. Contact Customer Care at 515-294-6826 for more information about the tests we offer.

How long do tests take?
Test duration depends upon the crop being tested and the type of test being performed. If you require more information than is available on this page, contact Customer Care at 515-294-6826.

What does "ISO 9001:2008" certified mean?
"The ISO 9000 (the International Organization for Standardization) family of standards represents an international consensus on good management practices with the aim of ensuring that the organization can time and time again deliver the product or services that:

—Meet the customer's quality requirements, and 
—applicable regulatory requirements, while aiming to 
—enhance customer satisfaction, and 
—achieve continual improvement of its performance in pursuit of these objectives." 

Our certification by an independent auditor means that the Iowa State University Seed Testing Laboratory has adopted—and follows—the absolute best possible procedures to benefit our customers. 

Where are the procedures obtained that are used for testing?
—AOSA — (The Association of Official Seed Analysts) Rules for Testing Seeds for domestic and international seed movement. 

—ISTA  (The International Seed Testing Association for international movement of seed. 

—Canadian M &P — Seed to be shipped into Canada. 

—NSHS — The National Seed Health System – phytosanitary testing 

—Biotech Trait Providers requirements — trait testing

Our ISO 9001:2008 certification is our guarantee to our customers that  rigorous standards are consistently applied to every test we perform.

Why are soybean germination tests that include hard and swollen seeds extended for up to five days?
The Association of Official Seed Analysts (AOSA) Rules for Testing Seeds allows any seed test to be extended an additional two days for reasons such as a slow growing seed lot (inbreds).  The Rules also allow for swollen seeds to be placed on new planting media and testing extended for up to five days.  Swollen seeds are hard seeds that at some point took up moisture during a germination test.  Hard seeds have a seed coat that doesn’t allow moisture to be taken up—often the result of hot and dry growing conditions.  Hard seededness is a desirable trait for species used in native planting, but is not a desirable trait for row crops where smaller plants might be crowded out.  Some seed species are mechanically scarified to break hardseedness (however, this is not the case in soybeans).

What tests are required for labeling purposes?
Labeling requirements require the following tests:
—Standard (Warm) Germination
—Noxious Weed Exam

How do soybean warm germ results typically compare with sand germ results?
Typically sand germination results are the same or slightly higher than warm germination results. In  instances of fungal problems or extremely dry seed, the sand germination can be  higher. We find that the higher the germination of the seed lot, the less positive effect the sand has on the results

What do cold test results in corn tell me about my seed lot?
Vigor tests are used in two ways: to "predict" field emergence and/or to rank seed lots. Since field conditions vary greatly from field to field and from year to year, no test can predict how a lot will do in all situations. However, cold test results typically correlate well  with field emergence for most lots. 

Tray (Iowa) cold tests correlate best with unfavorable conditions while saturated cold test results correlate better with even less favorable field conditions.  A 82% tray cold test result is usually considered to be the minimum acceptable for marketing a corn seed lot.

Is a cold test the preferred method for determining soybean vigor?
No, we recommend using the accelerated aging (AA) test.  Because the cold test does not typically stress soybean seed  much. Even though you would expect soybeans to be more sensitive to cold than corn, they don't actually seem to be. Another problem with cold tests on soybean seed is that  some years, there are a few lots that experience decayed unifoliate leaves in the cold test and can which  give lower than expected results.  Extremely dry seed (below 10%) can result in rapid imbibition (water uptake) damage in the cold test.  There is less chance of this in the AA test as water vapor gradually hydrates the seeds.

Why do I sometimes get high warm results and low cold results?
In general, carryover corn seed that is stored in cool, dry conditions maintains its viability and vigor well. Seed that is of low vigor or stored in less favorable conditions can  be expected to experience a drop in vigor from year to year (or even month to month).  A warm germ exposes the seed to "ideal" conditions. A seed lot with  little mechanical  or fungal damage or dead seed  after harvest would be expected to maintain its viability fairly well when stored correctly. But when the seed is stored in less favorable conditions, the seed ages more quickly and cannot tolerate the stressful conditions of most vigor tests

How do saturated cold results compare with regular cold results?
Usually saturated cold results compare well with cold test results. However, at times they are markedly different. It can be beneficial  to keep track of how a particular testing lab typically does on  various tests. Once you see how their tests compare to each other (germination vs. cold, cold vs. saturated cold, etc), then the results will be  more useful in determining the true viability and vigor of a seed lot.  The saturated cold test is often considered to  be a more severe test, but studies we have done comparing lab results to the field (different planting dates and conditions) show both tests correlating well with typical spring planting conditions.

What is an acceptable soybean accelerated aging (AA) result? In general, we advise that an AA result should be within 15% of an acceptable warm germ. What is acceptable varies from person to person, but most consider a 90% to be the minimum acceptable soybean germ most years. There are years when short supply of soybean seed can prompt the sale of lower germinating seed lots. But in a normal year, a 75% AA would be at the low end of a desirable AA results.

Why do I sometimes get higher soybean AA results than warm germination results?
There are two possible explanations: In seed lots with many seeds that have a light amount of Phomopsis on  cotyledons, the AA test reduces the harmful effects of the Phomopsis because it does not stand up well to the hot, humid conditions of the AA chamber. Seed with a heavier amount of Phomopsis have already had the damage done.

Some lots (especially of large-seeded edible soybean seed ) can have problems taking up moisture on Kimpak®. Gradual uptake of water during the aging period of the AA test and covering the seed with moist sand following the aging period can help some lots.

How can the Tetrazolium (TZ) test be utilized?
To check the viability of a seed sample in less time than a germination test (two days versus five days or more).
—To estimate the vigor of a sample of corn seed.
—To diagnose a problem seed lot (mechanical, fungal, or dryer damage or damage from maturing in the field. 
—To check the viability of ungerminated seeds in a warm germination test.

Can Tetrazolium results be used for labeling? 
Tetrazolium (TZ) results usually correlate well with warm germ results. However, they can be markedly different, especially in seed lots with fungal problems. The presence of fungi can be detected in a TZ test, but since the TZ test is a snapshot of the seed at about two days, it cannot detect how much the fungi will develop and hurt the seed by the end of the germination test. Labeling using the TZ test is not allowed except in a very few instances.