General Principles of Seed Storage
In view of the various factors affecting seed viability in storage, the following principles emerge as necessary for good storage.
a) Seed storage condition should be dry and cool.
b) Effective storage pest control.
c) Proper sanitation in seed stores.
d) Before placing seeds into storage they should be dried to safe moisture limits, appropriate for the storage system.
e) Storing of high quality seed only, i.e well cleaned , treated as well as of high germination with vigour and good pre-storage history.
f) Determine seed storage needs in view of period or length of storage time, and prevailing climate of the area during storage period.
Long term storage requires more exacting conditions of seed storage than short-term storage. Similarly, the regions with favourable storage climate, i.e one where relative humidity is rather low require less sophistication than areas of high relative humidity.
It is considerable importance to decide well in advanced how long it will be necessary to maintain the germination capacity of seed lot. Two types of problems that must be dealt with in seed storage are:
1. Pest Control
As the requirements become more exacting, the cost of storage facility per unit of seed stored increases rapidly.
Types of storage requirements. The types of storage needed can be related to the time of storage expected and can be classified into four types:
a) Storage of commercial seeds
b) Storage of carry-over seeds
c) Storage of foundation seed stocks
d) Storage for germ plasm seeds
a) Commercial Seeds:
The largest storage need 75 to 80 % is for the storage of seed from harvest until planting time, the next year. The storage period ranges from a few days to eight or nine months.
For most species, the requirements for seed storage are relatively simple. In the regions of no rainfall and low relative humidity, a smooth bare place may be reasonably satisfactory. However, loss from stealing, birds, and rodent s can be considerable and germination capacity can decline, at least in the surface seed, from heat damage and ultraviolet rays. Since it is not possible to have such a favourable climate every where, some shelter may be necessary. Such storage facilities can vary greatly. Successful storage structures and methods of storage for meeting the required needs should have following features.
i) Seeds placed in storage must be cleaned to free them of trash which may harbour insects or fungi and prevent free circulation of air.
ii) Seeds should be undamaged to minimise decline in vigour and germination.
iii) Seeds must be dried to a moisture content less than 14 percent for starchy seeds, and less than 11percent for oily seeds.
iv) Storage structure should be constructed so that the rain cannot enter, and that no serious gain in moisture will occur pests of stored seed should be effectively controlled if the following features for constructing warehouses are observed, and the other suggested measures are followed.
Construction Features for Good Seed Warehouse:
a) Warehouse should have no windows and have only one door constructed of metal which can be sealed properly and locked.
b) The material used for construction may be stone, concrete, brick, metal or wood. Regardless of the material, the foundation should be made of stone or concrete and should extend 90 cm above the ground level.
c) A lip around the building at the 90 cm height extending out 15 cm should also be constructed. Such construction makes entrance by rodents virtually impossible, as long as the foundation remains uncracked.
d) The floor must be paved and any cracks that may develop must be repaired.
e) Construction of the floor, walls and ceiling of the storage should be such that no cracks exist which can harbour insects. All cracks around openings, E.g Electric conduits, ventilation openings, and doors should be thoroughly sealed.
f) Ventilation openings should be screened against birds and insects.
Other Measures for Pest and Disease Control:
Good sanitation in the seed store is necessary for protection from insects and rodents. The tom seed bags should either be immediately repaired or replaced with new bags to avoid spillage in warehouse. All spilled seeds or floor sweepings should be immediately removed. Discarded seed and cleanings should be carried away, not just dumped outside the door and left to harbour storage insects. In addition to cleanings, the floor and walls should be sprayed with a residual insecticide as often as required. In a well – maintained store, spraying once a year may be quite satisfactory. The recommended materials and rates are DDT –( 50 percent WP) ½ to 1 lb/gal 1000 ft2 (1 to 2 g/m2) , Malathion ( 25 percent WP) 1lb/gal 1000 ft2 (1.25 g/m2). Malathion should not be used on such surface as brick, cement and concrete.
An insecticide combined with a fungicide may be applied as a protectant. The most commonly used insecticide is DDT. DDT also has the advantage of long duration.
Once the seed storage is completely free of insects, the most serious source of reinfestation is infested seed which is brought in seed may be brought from the field already infested, or it may be transferred from an infested storage. Such infestation is controlled by fumigation. Rather than fumigating the whole storage, it is better to have a fumigation room, or to fumigate the seed on a concrete floor under a tarpaulin before it enters the main storage room. The fumigation room should have its own door to the outside, and only after fumigation, should the seed be brought in to storage area.
Fumigation is effective only in gas-tight storage. Numerous effective fumigants are available. However, there is a small safety margin between the dose that is toxic to insects and a dose that will cause loss of germination or vigour of seed. Reasonably safe fumigants at temperatures below 30 0 C and seed moisture below 12 % are the following (Parking , 1963).
Methyl Bromide 16 to 32 oz per 1000 ft3 ( 16 to 32 mg per cubic metre)
Hydrogen cyanide 32 to 64 oz percent 1000 ft3 ( 32 to 64 mg per cubic metre)
Hydrogen Phosphide 5 to 10 tablets per metric ton of seed ( Phostoxin, Phosphine)
3 to 7 Days
It must be borne in mind that fumigation, particularly repeated fumigation, amy seriously reduce the vigour and even the germination capacity of seeds. This is particularly true of seeds with high moisture content. Seeds with moisture contents greater than 14 percent should be dried to below this value before fumigation. A high temperature also increases damage to seeds by fumigants. Hence, fumigation should be used only with entering seeds, and all other measures should be used to maintain insect control in the stored seed. Prophylactic biweekly or monthly fumigation of seed storages can lead to serious germination problems. It is far better to build an insect- proof storage, and make certain that seeds, bags or anything else placed in the storage are insect –free. Ofcourse, if a storage containing much seeds does become infested, then fumigation is required.
Seed Moisture Content:
To prevent damage from storage fungi, it is best to store seeds which have been well-dried to safe moisture content limits.