Several different tests can be utilized to determine the viability of a seed lot. While the tetrazolium (TZ) and accelerated aging (AA) tests provide useful information about seed quality, only the germination test is valid for labeling.
The germination test determines the percentage of normal seedlings that develop under specific, controlled conditions. Only seeds that produce all the essential, functional parts of a seedling are counted as normal seedlings. Any seedling that lacks essential parts to support normal plant growth is counted as abnormal. The percentages of dead seed, hard seed or dormant seed are also determined when present.
The tetrazolium test is a rapid, chemical viability test that can be used to estimate the results of the germination test. Seeds are soaked in the tetrazolium solution, then after a short time, analysts examine seed for stained tissue. Staining indicates actively respiring tissue capable of germinating. This test cannot be used as a substitute for the germination test in labeling seed.
The accelerated aging test is a high humidity, high temperature stress test that is an indicator of vigor. The test was originally developed to help estimate the viability of soybean seed after storage. It has been adapted for other crops such as dry beans and field peas. It is not suitable for small grains. The AA test must be done in conjunction with a germination test.