Seed storage : Maintaining seed viability and vigour for restoration use

Maintenance of seed vigor and viability in term germination from harvest until planting is of utmost importance in any seed production programme. Care should be taken at every stage of processing and distribution to maintain the viability and vigour. The harvested seeds of most of the orthodox crop seeds are usually dried end it stored for at least one season until the commencement of the next growing season, except those of the recalcitrant seeds which the requires high moisture content for safe storage (once dried the viability will be lost. E.g.- Jackfruit, Citrus, Coffee, Cocoa, etc. The dry weather alters moisture content of the seed, thereby reducing the viability. In most of the agricultural crops aging start at physiological maturity, which is irreversible. Hence seeds become practically worthless if they fail to give adequate plant stands in addition to healthy and vigorous plants. Good storage is therefore a basic requirement in seed production. The purpose of storages is to maintain the seed in good physical and physiological condition from the time they are harvested until the time they are planted. It is important to get adequate plant stand in addition to healthy and vigorous plants.

In order to preserve seed viability and vigor over the short term (a few weeks to a few months), seeds should be stored in a cool, dry, and rodent-proof location. Specific information on best practices for storing seed over the long term (several months to a year or more) is given below:

Store only new, mature, healthy and well-dried seeds.
Keep them in dry and cool place to extend their viability.
Seed stored at 60-degree Fahrenheit stays viable twice as long as seed stored at 70 degrees Fahrenheit.
The sum of the temperature in degree Fahrenheit and relative humidity should not exit 100. For example, if seed is stored at 50-degree Fahrenheit storing it at 40% humidity will work but storing it at 60% humidity is not recommended.
As a rule of thumb, the longevity of seed is halved for each 10 degrees increase in storage temperature, or 1% is increase in seed moisture content during storage.
Seeds easily re-absorb moisture. To maintain dryness, keep seed in tight containers like tin cans or glass jars with tight fitting lids.
Put in some moisture absorbing material. Dry wood ash, dry charcoal, powdered milk, toasted rice, or small pieces of newspapers are all good. The drying material should take up about ¼ of the container space.
If possible, include the initial percentage viability of the seeds. To do this, plant some seed to see how many germinate. If 8 of 10 germinate, for example, percent viability is 80%. This information will help us to learn about how much each type of seed loses viability between collection and planting.
Protect seeds from insects and fungi. Before storing in containers, mix with dry ash, powdered seeds of black pepper or neem leaves. Or use extract of neem, peanut, Castor bean or cotton: 1 teaspoon oil/ 1kg seed. Or use naphthalene balls:1 or 2 pieces/10kg seeds.
Protect from rodents and birds during storage.

Seed selection for extended storability

Store will mature seeds.
Store normal colored seeds.
Seed should be free from mechanical injury.
Seeds should not have met with adverse conditions during maturation.
Seeds should be dried to optimum moisture content.
Seeds should be treated with fungicide before storage.
Suitable packaging materials should be used for packing.

Factors affecting seed longevity

Kind or variety of seed: Seed storability is considerably influenced by the kind or variety of seeds. Some seeds are short lived. E.g.: Onion, Soybean and Groundnut. As a general rule starchy seeds can be stored considerably for a longer period compared to proteinaceous or oily seeds because of their hygroscopic nature.

Initial seed quality: Seed lots having plumpy, vigorous undamaged seeds store longer than that of deteriorated. Even seed lots having good germination at the beginning of storage period, may deteriorate at a faster rate depending upon the severity of weathering damage, mechanical injury or otherwise in the field. The low quality seeds should invariably be rejected. Even at best storage conditions, the initial quality of the seed cannot be improved (except for the dormant seed) but can only be maintained.

Moisture content: The most important factor influencing seed viability during storage is the moisture content and the rate of deterioration increases, as the seed moisture content increases. The drier the seed the higher will be the storage life.
Seed moisture content(%)———————————– storage life
11-13———————————————————- ½ year
10-12———————————————————- 1 year
9-11———————————————————- 2 year
8-10———————————————————- 4 year

It is well known that higher moisture content enhances the biological activity in the seeds and causes excessive heating, besides promoting mould and insect activities.

Relative humidity and temperature during storage

Seeds are hygroscopic. They attain rather specific and characteristic moisture content when subjected to given level of atmospheric humidity at a particular temperature (equilibrium moisture content). The equilibrium moisture content for a particular kind of seed at a given relative humidity tends to increase as temperature decreases and the deterioration starts.

Provenance

The seeds harvested in different climates (or) at different times show differences in viability. Because they would have been subjected to different pre harvest conditions which will have caused different amounts of deterioration by the time, the seeds are harvested.

The activity of organisms associated with seeds in storage

The bacteria, fungi, mites, insects, rodents and birds may do harm to seeds in storage.

Writer: Jyoti Kafle (Student, IAAS, Paklihawa, Rupandehi)