Seed Viability Test Carrying Methods
A seed is a basic element of any plant. The ovules after fertilization grow into seeds. A plant seed is made up of a seed coat and an embryo. The embryo is made up with a radicle, an embryonal axis and one (wheat, maize) or two cotyledons for example gram and pea. A seed is created inside a fruit which converts into a new plant when we plant it. Hence, the seed is a very important part. When should viability be determined? Viability will need to be determined at the start of storage and at regular intervals through storage to predict the correct time for regeneration of the accession. The viability test takes from a few days to weeks or even months to give an accurate product. If possible the results must be obtainable before the seeds are packaged and placed in the gene bank so that poor quality seeds can be recognized and regenerated before storage. Where the viability of seed cannot be determined before storage, the seeds must be placed in long-term storage to ensure their safety whilst awaiting the results of the test.
Seed testing is a very important aspect of a seed programme in India. The testing of seed samples was ready obligatory under the Seed Act, 1996 for the function of certification and for lowering enforcement. Seed testing is required to get the following objectives for minimizing the risks of planting low-quality seeds. To identify the quality problems and their probable cause through decides their quality that is their suitability for planting, to determine the need for drying and processing and specific procedures that must be used. To verify if seed meets established quality standards or labeling specifications. The main aim of the seed testing is to obtain accurate results regarding the quality status of the seed samples submitted to the seed testing laboratories. Why do we test seed viability? It is important to recognize that the seeds that are stored in a gene bank will grow to produce plants. Therefore, they must have high viability at the start and through storage. The viability of seeds at the start of storage will determine, within the environmental conditions, the storage life of the accession.
Methods of seed viability test:
Different methods of seed viability test will be given below;
The most accurate test of seed viability is the germination test. The germination test is made under controlled conditions to find out how many seeds will germinate and make normal seedlings which can develop into normal reproductively mature plants. The International Board for Plant Genetic Resources (IBPGR) Advisory Committee on Seed Storage recommends that for the initial germination test of species where a reasonable germination technique is available, a minimum of two replicates using 200 seeds (100 seeds per replicate) is suitable, providing that germination is above 90%. If not, a further 200 seeds must be tested as before and the overall result for seed viability taken as the mean of the two tests. Other biochemical tests are existing to test viability. These have the advantage of being quicker, but are not as accurate and want considerable skill and practice in their implementation and interpretation. These are not recommended by the IBPGR Advisory Committee on Seed Storage for common use as tests for seed viability.
Basic requirements for seed germination are water, oxygen, light and proper temperature. Seeds of different species have different requirements and no general set of situation can be relied upon to germinate seeds of all species. Seeds of some species are more tolerant and germinate in a wide range of conditions, but complete germination can be achieved under optimum conditions. Seed dormancy is seen when seeds imbibe water under proper temperature and light for germination but germination does not occur. How many seeds should be tested? A fixed model size germination test using 200 seeds in 4 replicates of 50 seeds is recommended as a best practice to determine viability at the beginning of storage.
Four replicates of 100 seeds are recommended based on the International Seed Testing Association (ISTA). However, best practices take into account the limited number of seeds obtainable and the aim of not wasting seeds in unnecessary testing. Overall seed viability must be taken as the mean of the replicates.
After the seed has made it to a new location and is covered with dirt, it can start germination. Germination is the procedure of seeds develops into new plants. First, environmental conditions must trigger the seed to produce. Generally, this is determined by how deep the seed is planted, water requirement, and temperature requirements. When water is plentiful, the seed fills with water this process known as imbibition. The water activates special proteins, called enzymes that begin the procedure of seed growth. First, the seed develops a root to access water underground. Next, the shoots, or growth above ground, start to appear. The seed sends a shoot towards the ground, where it will develop leaves to harvest energy from the sun. The leaves continue to grow towards the light source in a procedure called photomorphogenesis.
Many factors influence if, and how, seeds germinate. The main important factors are water availability, temperature, and sunlight. Water is very crucial to seed germination. The seed should go through imbibition to activate root growth. However, too much water can be a bad thing, as gardeners know. When a plant is still growing underground, during root development, it cannot use the sun to make food as most grown plants do. It must rely on the stored food in the seed, and oxygen from the environment to create energy. If the soil is soggy, there will not be enough oxygen and the plant will not thrive. Think about a person being set aside underwater.
Temperature is also a very important factor. A few seeds germinate when it is cold, such as plants in northern environments. Other seeds germinate when the weather gets to spring temperatures, which is why we see so much plant growth in the spring in temperate climates. Other seeds germinate after extreme temperatures, such as after a fire in the grasslands.
It determines the percentage of seeds that generate healthy root and shoot. In the laboratory, for most species the temperature range between 18 to 22°C, but for some species-specific temperature required. The duration of germination test varies from 7 to 28 days depending upon crop species. For cereals, seven days are enough.
The percentage of germination is equal to the ratio of a total number of seeds germinated to the total number of seeds planted.
In a germination test, a small section of seeds randomly selected from a larger seed lot is germinated. This process can be difficult or tedious since some seeds have special requirements, such as light, alternating temperatures, breaking a hard seed coat, or stratification.
Rolled Paper Towel Test:
For seeds that germinate easily, the proper temperature and moisture conditions need to be provided. One easy way to do this is to roll a sample from a seed lot in a moist paper towel, put in the roll into a plastic bag, and places it at the correct temperature for a sufficient time period.
Excised Embryo Test:
When the seed coat is impermeable to water or when the embryo requires after-ripening, the embryo should be excised. This process involves removing fruit parts and seed coats. Good sanitary conditions must be maintained since the exposed embryo is very susceptible to microbial attack. Seeds are viable if the cotyledons turn a green color and spread apart.
The aforementioned methods are regarded as an organic system of determining the viability of the seed. The chemical method is very effective and does not need much time like the germination test. It involves the use of a chemical identified as Tetrazolium; this chemical is poured on the seeds and the change in color of the seeds is observed.
Tetrazolium (TTC), 2, 3, 5-tri-phenyltetrazolium chloride, and stains living tissues red. This chemical can differentiate between viable and non-viable seeds, and an experienced technician can tell accurately how fresh and vigorous a seed is and whether or not vigor is decreasing. Highly viable seeds are uniformly red, whereas the seeds of reduced vigor are white and speckled white. Deeper red spots, particularly in low viability seeds, may represent microbial respiration.
If the seeds turn a reddish color, it means the seeds are viable and can germinate, but if no reaction is observed, it means the seeds are dead and will not germinate. The seeds can be washed and planted instantly.
This is the simplest technique of carrying out seed viability test. In this process, the seeds are poured into water and allowed to settle for about 30 minutes. After this period, a few seeds sink while some float. The sinking ones are the feasible once, that is, the good seeds, while the floating ones are the dead seeds. Hence, the floating ones are poured out through the ones that sank are fit for planting.
The water seed viability test:
A quick and easy seed viability test that is often recommended is to see if seeds float in water. To perform a water seed viability test, take a Mason jar or deep dish and fill it with water. Get the seeds you’re unsure of and pour them into the container with water. Let seeds sit in the water for about 20 minutes. If the seed float they are probable to be poor germination. However, if a seed sinks to the bottom of the container, they should still be viable.
There are a couple of issues with this seed viability test, but it is a quick method of checking older seeds as you are planting. Sometimes seeds just float. So just because a seed doesn’t sink to the bottom doesn’t mean that should toss them and not plant them in your garden. Go ahead and plant this floating seeds, too.
These are simple methods to determine if a seed is viable or not. Farmers must ensure they find out the viability of their seed, irrespective of the source of the seed. It helps to protect the investment and assure the farmer of a good return.