Types of Seed Viability and Vigour Tests
It is critical to understand that seeds deposited in a gene bank will develop into plants. As a result, they must be highly viable at the outset and during storage. The viability of seeds at the beginning of storage will also define the accession’s storage life, given the environmental parameters.
Why should we test seeds for germination?
The importance of seed testing precedes several centuries. There are several reasons why we must test seeds and provide a basis for price and consumer discrimination among different types of seeds in the market. Here are some objectives why seed testing is important:
- To establish their quality, i.e., whether or not they are suitable for planting.
- To establish the requirement for drying and processing, as well as the specific procedures to follow.
- To determine if seed satisfies defined quality criteria or labeling requirements.
- To determine the source of the quality issue and the most likely reason for the same.
How is seed viability determined?
Seed viability testing is essential for seed conservation monitoring. Depending on the species, it might take anything from a few days to weeks. While many different tests exist to test seed viability, here are few critical tests that accurately determine seed viability:
Physical purity testing is an analysis used to classify a seed lot’s makeup. It’s crucial for determining if a particular seed sample meets the required purity criteria and can accurately reflect the seed lot. By hand, blowers, or sieves, the working sample is usually divided into four components (purity seeds, other crop seeds, weed seeds, and inert materials), and the proportion of each component is then measured by weight.
- Parts of the working sample that reflect the crop species being examined are known as pure seeds. All botanical variations of that kind/species are included in the pure seeds section. Immature, sick, shriveled, damaged (>1/2 of their original size), or germinated seeds are also included.
- Other crop seeds are crop seeds that are not related to the crop species being studied; they generally make up less than 5% of the overall sample weight.
- Weed seeds are seeds that have been designated as weeds by legislation, rules, or common use.
- Structures, stems, leaves, sand and stone particles, empty glumes, lemmas, paleas, chaff, awns, spikelets, and other non-seed components are examples of inert substances.
Standard Germination Test
Germination is described in seed testing as “the emergence and development of those critical structures from the seed embryo that, for the sort of seed tested, indicate its capacity to grow into a normal plant given suitable soil circumstances.”
Seedlings that lack an important structure, have a poor or unbalanced development, or have decay or damage that interferes with the normal growth of the seedling are not included in the germination percentage calculation. Diseased seed, old seed, mechanically damaged seed, seed kept in high moisture, and excessive heating of seed during storage or drying are all factors that might impair seed performance in germination tests.
Determining Moisture Content
The quantity of water in a seed is measured by its moisture content (mc). In any seed-testing facility, it is normally given as a percentage on a wet weight basis. The moisture level of the seed is the most important factor that affects the seed’s quality and storage life. Seed moisture content is linked to a number of physiological seed quality factors. Seed maturity, optimum harvest timing, mechanical damage, economics of artificial seed drying, seed lifetime, and insect & disease infestation are just a few examples.
Quick Viability Test by Tetrazolium Chloride
The quick viability test is also known as the Tetrazolium Chloride (TZ) test. It’s a chemical test that determines seed viability, and it normally takes 24 to 48 hours to get results. The TZ test can provide an early and rapid indication of seed viability, but it is not a substitute for a more thorough seed germination test.
It works by the following method: By hydrogen transfer process catalyzed by cellular dehydrogenases, all respiring tissues may transform a colourless chemical, TZ (2,3,5 triphenyl tetrazolium chloride), to a carmine red coloured water-insoluble formazan. TZ penetrates both live and dead cells, but only living cells catalyse the synthesis of formazan, which is non-diffusible and colours the viable seeds red, but the lack of respiration precludes formazan production, leaving the dead seeds (aged tissue) uncolored.
Accelerated Aging Test
The Accelerate Aging test uses increased temperatures to artificially speed up the aging process in order to imitate real-time aging. Manufacturers may use this test to get their product to market faster. Accelerated aging is optional, however when determining an expiry date, real-time aging is necessary.
A cold germination test is used to assess a seed lot’s ability to germinate in cold, damp soils, which can result in poor field performance. The cold test was created to imitate harsh field conditions and assess seed emergence capabilities. For maize and soybeans, it is the most extensively used vigour test.
The vigour of seeds is influenced by a variety of genetic and environmental variables, as well as crop management decisions made during seed development. Variety, weather conditions during seed growth and maturity, mechanical damage during harvest or cleaning, insufficient drying, and improper storage conditions are all aspects to consider. Although such conditions may impact the vigour of the seeds, their effects may not be shown in routine germination test findings. Only more severe examinations, such as vigour tests, can identify these effects. Speak to Gubba to learn more about seed viability and vigour testing.
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