Seed viability and vigor: Capable of Germination
A viable seed is one which is capable of germination under suitable conditions. The definition includes dormant but viable seeds, in which case the dormancy must be broken before viability can be measured by germination. A non-viable seed, therefore, is one which fails to germinate even under optimal conditions, including treatments for the removal of dormancy. The practical definition of viability depends upon the context in which it is used; for example, to the ecologist, viability implies the ability of the seed to germinate and the ability of the seedling to establish itself in the environment in which the seed finds itself. However, when seeds are utilized, to produce a crop, for example, then viability is a measure of the suitability of the seed batch to produce a satisfactory crop.
Seed vigor is the speed of germination. It is the sum total of those properties of the seed that determine the potential level of activity and performance of the seed during germination and seedling emergence. Seed vigour is an important component of seed quality and satisfactory levelsare necessary in addition to traditional quality criteria of moisture, purity, germina-tion and seed health to obtain optimum plant stand and high production of crops.As agricultural and horticultural techniques become progressively more sophisticated, the need for high vigour seedS will increase and testing standards, similar to those reconginzed for germination will be required
A seed’s vigour determines how well it performs, its ability to yield strong seedling that become robust and uniform plants. On other hand, seeds seen to be low in vigour will produce weaker seedlings that will be more susceptible to attack, contamination and other environment issues. When seed is purchased , the germination percentage expressed on the seed tag is the result of a worm germination text conducted under nearly ideal condition. A cold vigor text more nearly approximate the conditions under which many seeds actually germinate in a field.
Generally, large seed has better field performance than small seed. Seed size os positively correlated with seed vigor, larger seeds tend to produce more vigorous seedlings. Several factors like genetic constitution , environment and nutrition of mother plant, maturity at harvest seed weight and size are known to influence seed vigour. Two criteria have been employed to evaluated the performance of seed vigour test methods for different crops.
1) Reproducibility of vigour method.
2)The relationship between vigour test results and seedling emergency in field soil.
There is no universally accepted vigour test for all kinds of seeds. The determination of following vigour tests will be useful in gaining additional information on seed quality.
1) Growth Tests
2) Conductivity Tests
3) Brick Gravel Test
4) Paper piercing Test
5) Cold Test
6) Accelerated Ageing Test
Why do we test seed viability? It is important to know that the seeds that are stored in a genebank will grow to produce plants. The viability of seeds at the start of storage will also determine, within the environmental conditions, the storage life of the accession.
Three common method of testing seed viability:
1. evaluation (examining the seed for a color change in the embryo)
2. Purity test: The percentage of seed described on the label that is actually found in the quantity of seed.
3. Weed test: Examines a sample of seed and identifies every seed that is different from the labeled seed kind
The scientific way to test seed viability is Tetrazolim chloride seed testing: The Tetrazolium Chloride (TZ) test is often called the quick germination test. It’s a chemical test used to determine seed viability, and results are usually available within 24 to 48 hours.
Testing the viability of seeds by conducting a seed germination test is an important way to deduce the quality of your seeds, to determine the efficiency of seed storage method and to help plant tje proper amount of seeds.
Writer: Susmita Adhikari (Student, Bsc Ag. 4th sem, IAAS Paklihawa)