Both lots of seed are viable, but Lot A has lower vigour than Lot B because it takes
longer to germinate. This characteristic of low vigour often only becomes apparent in
poor conditions for germination - in this case, low temperature.
))
The example above shows that even when a seed lot has a good germination rate when
tested in ideal conditions in a laboratory or at home, it will very often germinate either
less or more slowly when it is planted out in the field. With sorghum, for example, a
laboratory germination test of 90% may give only about 50% germination in field
conditions.
Seed Longevity (Storage Life)
In ideal storage conditions such as those maintained in a plant gene bank (about -20°C
and 5% relative humidity), seed of most species will remain viable and vigorous for
many years. But in real life seed is never stored this way, and it is also often transported
long distances and handled roughly, which can be very damaging to fragile seed such as
soybean or groundnuts.
In general, seed loses its germination more rapidly when stored in hot and humid
places than in cool dry ones. Seed with a high moisture content also loses viability more
rapidly than dry seed.
As usual in agriculture there are no hard and fast rules, and for this reason the
following points should be noted:
- test seed before it is distributed, if at all possible;
- try to store seed for as short a time as possible, especially in hot or humid
conditions; - transport seed to more favourable storage conditions if it has to be stored for a long
time; - handle seed very gently—it is a living organism. Avoid throwing or dropping sacks
etc.
Approximate Seed Longevity:
1–2 years: maize, okra, parsley, parsnips, soybean
3 years: asparagus, beans, leeks
4 years: beet, chard, pepper, pumpkin
5 years: broccoli, cauliflower, celery, cucumber, eggplant, lettuce, muskmelon,
radishes, spinach, squash, turnip, watermelon
5+ years: cucumber, finger millet, teff
Recalcitrant Seed
As noted above, seed remains viable for longer when its moisture content and storage
temperature is reduced. However some species have what is known as recalcitrant seed
which does not obey these laws and which is killed when their moisture content is
reduced below a relatively high value. All such species are perennial.
Examples: cocoa, palm-oil, coconut, avocado, mango, mangosteen, durian, rambutan,
langsat, jackfruit, oak, chestnut and horse chestnut.
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GROWING FOOD – THE FOOD PRODUCTION HANDBOOK
)) A Word of Caution about Germination Tests