Understanding Vigor Scores

Germination testing is a key component in providing quality seed to the producer. It provides assurances that the product is of good quality and provides confidence to the farmer who plants the product. A germination test is an indication of the seed’s maximum viability and thus provides an understanding of how a particular lot of seed will perform under ideal conditions. With this knowledge, a farmer can decide whether to purchase the product and, if so, can determine the seeding rate to use.

Is there a difference between germination and seed vigor?

All viable seeds will germinate if placed under the proper conditions of moisture, temperature, and oxygen. Seed vigor is defined by the International Seed Testing Association (ISTA) as the “sum of those properties that determine the activity and performance of seed lots of acceptable germination in a wide range of environments”.¹ Seed vigor is not a single property, but rather a combination of variables such as the rate, uniformity of germination, and growth of seeds under suboptimal growing conditions. It can also measure performance after storage, particularly the retention of the ability to germinate.

How is germination and vigor assessed?

The two major types of tests that Bayer uses are the:

• Warm Germination Test (WGT): a standardized test using the protocols approved by the Association of Official Seed Analysts (AOSA) and is required by the Federal Seed Act and state seed laws. The WGT determines the seed’s ability to germinate in ideal conditions. The result of this test is required to be included on seed labeling and is only valid for a prescribed period of time. WGT results are comparable across seed providers because the test methods are standardized as prescribed by law.
• Vigor Test: is not required by law and is not standardized across the agriculture industry. It determines the seed’s ability to germinate under less than ideal (typically cold) conditions. Because test methods among seed providers and seed testing laboratories can differ, the results of these tests should not be compared against one another as are WGT results.

Figure 1. Warm and cold germination tests. These images were taken at the end of the test. They demonstrate the extreme phenotypic difference between seedlings in the two tests.

The emergence of seedlings in my field is lower than the WGT indicated, was the test wrong?

The vigor test is more similar to the conditions in which many seeds actually germinate under field conditions. The WGT determines the ability of seed to produce a stand under favorable environmental conditions. When compared to actual field performance, the WGT usually overestimates field emergence, primarily because field conditions are usually less than ideal. This is why the standard recommendation is to increase seeding rates by 5 to 10% above the desired stand when seeding under less than ideal conditions.²

The vigor tests attempt to more closely simulate field conditions at planting time. As planting date becomes earlier, germination and emergence conditions become harsher because of cooler soils.

Does seed vigor affect later plant growth?

When plant height, stem diameter, and leaf area at V4 and V8 growth stages were compared among different lots of seed with varying vigor scores, all three factors increased in value when the percentage of seeds with higher vigor was increased.³ However, this response can be influenced by the post emergence environmental conditions.

Bayer has developed a proprietary vigor test that we believe more consistently predicts emergence across the varied environments in which the crop may be planted. Also, WGT and vigor test are only two components of our robust quality management system used to provide the highest quality seed available to our customers world-wide. Based on the timing requirements for the WGT, you can be assured that the germination score on your seed (which includes the date the test was performed) is relevant to help make planting decisions.

Bayer stands behind the quality of the products and growers should have confidence in each bag of seed purchased.

Sources:

¹Understanding seed vigor. 1995. International Seed Testing Association. https://www.seedtest.org/upload/prj/product/UnderstandingSeedVigourPamphlet.pdf

²Nielsen, R. 2020. Plant populations for corn in Indiana. Purdue University Extension. https://www.agry.purdue.edu/ext/corn/news/articles_20/PlantPopulation_20200326.html

³Vaz MondoI, V., CiceroI, S., Dourado-NetoI, D., PupimI, T., Neves Dias, M. 2013. Seed vigor and initial growth of corn crop. Journal Seed Science. https://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-15372013000100009

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