- introduction to avoiding losses
What is the most important thing about handling seeds?
Remembering that they need to be looked after if they are to remain alive and able to germinate.
But aren't seeds resting stages that don't need the care that seedlings do?
some tree seeds are not really resting organs, but start to germinate immediately (B 13);
Other kinds of seeds are resting organs, that can be dried and stored (B 33); but
Most seeds are liable to die, if they are subjected to:
So it's better to think of them as delicate?
Yes; a potential seed crop needs looking after throughout the flowering, fruiting and collection periods; and then right up until the seeds are sown.
Why starting as early as that?
Because there may be steps that can be taken to increase the chance of collecting viable seeds. For example:
But how can I do anything about animals eating the fruits?
Well, one can concentrate on reducing the number of fruits taken, for instance by:
How about seed pests?
Substantial losses of potential seed supplies, and seedlings with missing parts and poor growth, can sometimes be caused by:
If unchecked, some pests can spread within the tree nursery, giving continuing trouble.
Can anything be done about insects?
Ways of reducing insect attack can usually be developed (C 45 in Manual 3), especially when their life-cycle has been studied. For example, you could:
And what about rodents?
They can usually be kept out by:
Setting traps, or keeping a cat, can also help keep the numbers down.
How about seed diseases?
There are three main types:
What kinds of rough handling should be avoided?
Moist seeds (B 12–13), and especially those that have already started to germinate (B 44) need particular care.
How about high temperatures?
Dry seeds are often more tolerant of heat than their seedlings are, and some can stand
temperatures of 40–50°C, but hot conditions like this should generally be avoided.
Most moist seeds could be damaged or killed by such temperatures, even if they occurred for less than an hour. For instance, cocoa beans for consumption are often dried in full sun on the edge of a road, but those to be sown need to be kept much cooler and moister or planted immediately.
So how should seeds be dried, then?
See sheet B 33 for the general principles for dry seeds, and remember that moist seeds may need to be sown at once (B 13), or dried reasonably slowly. Rapid drying can impose too much stress on the cells (C 10 in Manual 3).
A method suitable for one tree species will not necessarily be appropriate for all the others.
But mightn't the seeds go mouldy if they are not dried quickly?
Sometimes yes, if drying is too slow, or if large piles of fruits or seeds are left without being
turned over periodically; but
Usually no, if the air can circulate freely.
Aren't low temperatures good for storing seeds?
Not necessarily, because of chilling injury (D 11 in Manual 4) to moist tissues of many
tropical species at the temperatures in a refrigerator (about 4–14°C).
However, after careful drying, some kinds are indeed best stored cold, and some can even stand being kept in a deep-freeze at temperatures of about -10°C to -20°C.
Where is the best place to keep those where low temperatures are harmful?
In a dry and airy place (B 33), protected from rodents. If an air-conditioned room is available (around 18–23°C), this could be ideal, but not if the electricity supply is liable to go off for long periods at a time.
How often should I check seeds?
Every day for recent collections which have not yet been dealt with;
Twice a week for seeds that are drying and may need turning;
Once a week for batches of species which are prone to attack; and
Once in 3 months for dried, protected seed in longer-term storage.
What do I need to look for when checking?
Any signs of a bad smell or mould developing, discolouring of some seeds, or the droppings of insects or mice.
- fruit and seed collection
What are the most important points about collecting seeds?
If seeds are being collected from experiments, assisted pollinations or controlled crosses (B 23), it is important to keep each batch separate.
When should fruits be collected?
At or close to the time they become fully ripe (B 12). For each species, one needs to judge
how to strike a balance between collecting:
too early, when seeds might not be completely developed, while those the tree sheds first may be empty; and
too late, when most fruits might already have been eaten or the seeds dispersed.
Harvesting fleshy fruits for human consumption is often best done a little earlier, while they are still firm, if they will finish ripening after picking.
Supposing they don't all ripen together?
In some species, fruiting is spread over weeks or months, while in others all the fruits ripen at about the same time. In the former case, several collections may need to be made, but that could mean greater flexibility in arranging the collection to fit with the time for sowing the seeds (B 43).
What are the different ways of collecting seeds?
Which is the best?
It is often preferable to collect fruits (or cones) before they fall or release their seeds (B 12), because:
But picking the fruits will involve climbing, won't it?
Yes, it usually does, except for:
How do they work?
The simplest kind is just a long pole which is used to knock down the fruits. Alternatively an open bag, basket or tin is attached to a long piece of bamboo, so that fruits or seeds can be collected by pushing at the fruit when it has been manoeuvred inside. A somewhat more sophisticated version is the ‘fruit-picker’ which also incorporates a blade to cut the fruit stalk, and sometimes a pole in sections that can be screwed into one another.
What climbing methods can be used?
How can the trunk of a tree be climbed directly?
In some parts of the tropics, ladders are attached to the trunks of trees in order to make successive collections of honey from wild bees. Where appropriate, these could also be used for seed collection.
But the fruits are usually out in the crown, away from the trunk!
Yes indeed, except for those species where the fruits are borne on the trunk (B 11). So there is generally a second stage to fruit collection, in which the climber has to reach some of the fruits and detach them, or push at their stalks with a short pole.
Are there some safety guide-lines?
How about using a collecting sheet on the ground?
This is more likely to be successful if the:
What materials would be suitable?
Anything that is large enough, such as cloth, plastic shadecloth (A 24 in Manual 1), closely woven mats, roofing panels or old pieces of plywood.
Polythene sheeting can sometimes be used, but you may find problems with:
- seed extraction and cleaning
Do seeds always need extracting?
No; because sometimes they are:
Aren't all the other kinds too diverse for one method to apply?
Well, fruits and cones do differ greatly in their nature, size and the number of seeds they contain, and so the appropriate ways of handling them vary in detail. However, they can be broadly divided into:
Note: try and avoid damaging the seeds during extraction and cleaning! Seeds with hard coats (B 13, B 34) are generally less delicate than those that are soft.
|Sometimes seeds are hard to extract.|
How can seeds best be extracted from fleshy fruits?
Firstly, they should be pulled open or chopped up, without damaging too many seeds;
Secondly, the seeds need to be separated from the fruit pulp, which can usually be done by washing, sieving and rinsing, which also cleans them; and
Thirdly, the water should be allowed to drain away from the seeds, so that they become surface-dry and less likely to start rotting.
Can they be left to steep in water?
This can often help to soften the fruit tissues, provided that:
Are there some other general points about fleshy fruits?
Sometimes seeds just fall out.
And are there some general methods for dry fruits?
If necessary, shake or sieve to extract the rest of the seeds.
What about dry fruits that don't open up?
These are more difficult. For instance:
Supposing I want to try strong chemicals?
You could do a small experiment (B 48), remembering that:
And what about fruits with a single seed?
Usually they do not need to be extracted, but can be handled like seeds. Examples include Terminalia, which can usually be dried and stored, and the 2-seeded fruits of many diptercarps, which cannot.
Do all kinds of seeds need to be cleaned?
No, although most of them do. As well as removing most fruit remnants, twigs and leaves, cleaning may involve:
Supposing the cleaned seeds quickly start to rot?
There are four possible explanations:
spreading the washed seeds out more thinly for better drying;
dusting them with a fungicide such as propamocarb (B 47) before storing or sowing;
the seed-lot is infested with the resting stages of fungi or bacteria, when you could treat them as under (2); or
the seeds were empty or dead in the first place (B 13).
Where should I keep the cleaned seeds?
Immediately they are clean, make a choice between:
- drying and storing seeds
Which kinds of tree seeds can be dried for storing?
So what needs to be done with those that cannot be dried and stored?
Usually they need to be sown at once, or within 1–2 days.
Isn't that sometimes rather inconvenient?
Yes, especially when:
Can anything be done about it?
Here are some suggestions:
What is the best way to handle the kinds of seeds which can be dried?
By extracting and cleaning (B 32) the batch promptly, and then:
Where would be a good place to dry them?
Somewhere under cover where they are protected from rain and strong winds, and also from animals (B 30), but not in still, moist air that might encourage moulds to grow.
Air-conditioned rooms can provide ideal conditions for drying many tropical seeds, as the air is dry, cool but not too cold, and is moved about and replenished by the fan.
Special seed kilns are used in seed testing laboratories.
How fast can I dry seeds?
Aim for a moderate rate of drying:
Tests suggested that Triplochiton scleroxylon fruits are best dried at a moderately slow rate of about 1% of their original weight each hour (see Longman et al., 1978 in B 52).
How dry do they need to be?
This tropical species stored best at 8–14% moisture content.
Experience in the USA suggests that a wide range of seeds stored best at 5–12% moisture content, although there were examples below 1% and as high as 30%.
But how can I tell how dry my seeds are?
An accurate determination is not usually practicable for the smaller grower. However, it is a reasonably straightforward job in a seed-testing laboratory, where different drying regimes can be tested using a large seed-lot, and then recommended procedures worked out for those who do not have facilities for accurate weighing of seed samples.
How is moisture content determined?
How do you get the samples to be equivalent?
For larger seeds, you could count out a standard number, for instance between 15 and 30.
For smaller seeds, you could take a standard fresh weight, say between 50 g and 150 g.
Why not use the fresh weights of the living seeds as the standard, so that it was not necessary to destroy any of them by strong heating and drying?
Yes, that would be much easier, but fresh weights are so changeable that they would make
too unreliable a standard for accurate studies.
For the grower, however, fresh weights can be give a rough guide of the rate of drying, and also for instance to:
What is a seed kiln?
A drying ‘oven’ in which the air humidity and temperature can be controlled, so that pre-set drying regimes can be routinely applied to seed-lots.
So it's no use to smaller growers, then!
It could be if you:
What kinds of containers can be used to store seeds?
There are basically two approaches:
Which is best?
Bags are the most suitable in many cases, provided that they can be kept in cool, dry
conditions, and protected from pests (B 30). The seeds can then dry further in storage,
rather than going mouldy.
Sealed containers are preferable when already dry seeds need protection from a humid atmosphere. Note: when a sealed container is cooled in a refrigerator, the relative humidity of the air inside increases, and the moisture content of the seeds may rise.
And what kind of practical storage conditions are usually best?
These vary quite a lot from species to species, but in general seeds remain viable longer in dry, cool conditions that do not fluctuate greatly.
How cold is suitable for tropical trees?
Seeds can be stored:
For instance, Triplochiton scleroxylon fruits that had been dried in the way described above kept for 18 months at - 18°C with little loss of viability.
How long will my seeds keep alive in storage?
This can vary from a few weeks to several years.
If every seedling will be needed, it might be better to sow the whole batch soon, before any viability is lost.
If you have plenty of seeds, viability can be checked (B 48) from time to time by:
NOTE: bear in mind that seeds that do not germinate may be dormant rather than dead (B 13).
What about longer-term storage?
This is particularly needed when:
Long-term storage of seed (and sometimes of pollen) is a job for a specialised centre, where:
Are there any unusual ways of keeping seeds alive longer?
Yes. For example:
- pre-sowing treatments
What are pre-sowing treatments?
In the narrow sense, they are ways of breaking any seed dormancy (B 13) that may be present;
In the wide sense, they also include anything else that needs to be done to the seeds before they are sown, in order for them to germinate successfully, such as:
Which kinds of pre-treatments do dormant seeds require?
These are described in sheet B 13 for the commonest types of dormancy.
When should they be done?
Dry abrasion of ‘hard’ coats is generally best done 1–2 days before sowing, because it may
let in moisture and resting stages of moulds that could shorten the storage life;
Treatment in liquids needs to be done shortly before sowing, as the seeds will be wet.
Other types of dormancy often involve providing specific germination conditions.
Why should seed temperatures be altered gradually?
Because sudden changes impose an extra and unnecessary stress on the living cells in the
seed, which have been remaining alive at a very low rate of activity (C 14 in Manual 3).
For example dry, unmilled rice grains can remain viable when stored in a deep-freeze, but none will germinate if they are put straight into water at 25–30 C.
Is there a simple way of avoiding sudden temperature change?
You could let seeds warm up slowly by wrapping the unopened seed containers in a thick layer of newspaper, and leaving them in a shady place for 6–24 hours.
But I might want to open the containers to take out some seeds and keep the others in store!
Yes, you might; but opening a container while it is still cold from the refrigerator or deep-freeze will mean that water is immediately deposited on the seeds inside, just as happens on the outside of a cold drinks bottle or can. This cold water:
One way of getting over this problem is to store the dried seeds in several smaller containers, rather than a single large one.
Is soaking in water always necessary for dry seeds.
No. Sometimes it is better to let them take up water from the moist germination medium (B 42) after sowing (B 43).
Which kinds do need soaking first?
Those in which the entry of entry of water is slow, because:
Pre-soaking can also lead to more uniform germination of all the viable seeds, which can be an advantage, particularly when growing seedlings for research (C 7 in Manual 3).
How can seeds be pre-treated against diseases and pests?
If these are liable to cause problems, seeds can be coated with small quantities of an appropriate powder, or soaked briefly in a diluted solution (B 47). Alternatively, in difficult cases a small amount of fungicide could be incorporated in the germination medium.
NOTE: always wash your hands well after using any of these poisonous chemicals!
For most species, however, proper seed handling and protection (B 30–34), coupled with good germination conditions (B 40–47), mean that such pre-treatment may be unnecessary.