​

Collection

 

As has already been emphasised, for those subjects that are available locally, the most satisfactory system of seedling production is one based on the collection of the seed ‘in house’. This allows the confirmation of parental identity, an assessment of the quality of the crop and the potential to harvest the seed at a particular moment of maturity. This does not however preclude obtaining material from reliable correspondents with access to particular individual specimens and/or stands in cultivation or in the wild and who have the ability to transmit the material quickly and effectively and who are in a position to follow the designated protocols. Thus if the nursery is operating with an extensive catalogue grown in relatively small quantities and only small samples of seed are required annually - then self collection for much of the list (and hence known provenance) may accrue benefits.

 

In spite of this recommendation the economics of this mode of collection must be assessed in relation to the benefits when compared with commercial sourcing. For subjects that do not lose water readily or do not lose viability quickly or do not have dormancy issues then commercial sourcing will probably be a relevant resource.

 

The objective in the collection of seeds is to harvest high quality seeds in such a way that there is no detriment to the integrity and condition of the seed and its contents - so that the highest level of viability and condition is maintained.  

 

It is not sensible to waste time and resources collecting poor or substandard samples of seed.

 

The collection of seeds (and/or fruits) requires a number of preliminaries to be considered:-

a) designate the source and confirm an identification.

b) assess the quality.

c) obtain the necessary permissions to collect (if such are required or as a courtesy).

d) gear up – ie assemble the required kit for collecting, labels, packets and containers, cool boxes for removing field heat and for transporting the sample.

e) determine the quantity needed and assess whether this is available – this should be monitored through the season.

f) schedule the collection when the seeds or fruits have reached the required stage of maturity so that they can be gathered easily or when the dormancy avoidance dictates or before the critters deem them palatable.

 

The actual collection will require some attention:-

a) Collection when conditions are suitable

b) Adopt suitable methods to avoid detriment to the seed or the parent tree or shrub.

c) Wear any protective equipment - gloves, smog masks etc, when necessary, to avoid allergic reactions etc

d) As even small quantities of (especially) big seeds or fruits are likely to ‘heat up’ as a result of their normal metabolic activity – the material should be packeted in ‘small’ units and it would be prudent to provide a cool box for temporary storage and transport in order to remove the ‘field heat’.

e) Collect as clean a sample as is feasible – remove leaves and other detritus as you go.

 

Extraction

 

The objective in the extraction, of a sample of seed from its surrounding fruit, is to avoid damage to or cause any detriment to the structure and integrity of the seed and its contents or to reduce the level of viability or to affect any dormancy conditions.

 

The extraction of seeds from the fruit is determined by one of the following processes:-

a)) separation of the seed from the remainder of the fruit, in order to obtain a clean and unadulterated sample;

b) separation of the seeds from multiseeded fruits into single entities;

c) isolation of the seeds from the flesh or other materials constituting the fruit (which may contain germination inhibitors or harbour agencies which may be detrimental to the survival of the seed).

 

The process should be achieved

a) with the minimum of damage to the physical integrity of the seed;

b) with the retention of acceptable levels of quality;

c) without altering the internal physiology of the seed and especially without enhancing any dormancy conditions or inducing secondary dormancy;

d) without enhancing any seed coat condition associated with moisture permeability and

e) without critically affecting the moisture content of the seed.

 

The actual methods of extraction are as disparate and diverse as the individual types of fruit themselves. It is possible to describe various generalised methods of seed extraction but it is to be emphasised that each sample should be dealt with and organised on an individual basis. The process should be monitored continuously in order to modify the action of equipment or the treatment process itself to suit each sample and that regular assessment is made of the status of the seed in order to maintain quality control and so produce a sample with the highest capacity to regenerate.

 

Drying

Those plants which liberate their seeds from the fruits simply as a result of drying – is a common process - and as water is withdrawn by the parent or is lost by the action of external agencies, the fruits mature to the point at which they open or release the seeds. It would appear that within rough parameters this process is sequential. The process will proceed as the fruits gradually dry, or the fruits may disintegrate or even explode – depending on their mode of dispersal. Fruits of this type therefore will generally be collected as they become fully mature and reach the point at which they are approaching the stage at which they will open to disperse the seeds.

 

In many species of plants the seeds are liberated from the fruit as a result of the withdrawal or loss of water from the fruit tissues until such time as a point of weakness is triggered and the seeds are gradually exposed or even explosively ejected. The time of collection however prior to this stage is often critical as drying of the fruits, using an artificial (hence external) source, will not necessarily produce the correct drying process (sequence) and the points of weakness will not be triggered and the fruits will remain stubbornly closed – Ceanothus, Euonymus, Magnolia.

 

The cones of conifers, in general (ie not those producing a fleshy fruit or serotinous cones), normally open and liberate their seeds as a result of a natural drying process. As harvested cones are necessarily collected before they open and liberate their seeds, the cones can be dried artificially in gentle, dry warmth when they will respond without difficulty and open successfully. On a large scale this activity can be undertaken in a suitable ‘kiln’ - in which the cones can be tumbled dried at no more than 60˚C. This will achieve satisfactory results and a clean sample of seeds will be produced. If the cones are of the type which break up to liberate the seeds it will be necessary to fan the resulting mass to separate the seeds from the scales.

 

Serotinous cones can usually be opened by flaming them over a fire; however if they are particularly tightly closed and do not respond they should be soaked, then frozen and then thawed and dried. The seeds will then shake out once the scales open.

 

Fleshy Fruits

Fleshy fruits, of whatever construction (drupes, pomes, berries, arils etc), have generally evolved as a mode of dispersal for the seed and represent the various ways of attracting an animal vector by providing a food resource. The same strategy has developed in many other genera where the outer tissues of the seed have adapted for the same purpose once the fruit case has opened (eg Euonymus, Magnolia). The attraction to the vector is often enhanced by the development of colour which identifies the food resource and the stage of development in terms of palatability and food value. This type of strategy also provides for the possibility of an extensive distribution of the seeds especially with birds - which can cover large distances while the seed is still in the gut. Fruits and seeds of this type will, more often than not, contain seeds with a ‘hard’ seed coat condition – this provides the protection for the seed to avoid damage as it passes through the gut and the various digestive processes and if all has gone to plan the seed coat will have been degraded close the level allowing water permeability when it is eventually expelled. Artificial extraction does not achieve this degradation so that it is important that the process does not enhance the condition – which usually occurs when the seed is dried more than is necessary.

 

The process used for extraction of the seeds is to macerate and ferment the fleshy fruits in water under warm conditions until the seeds begin to separate from the flesh, at this stage mild agitation will cause the seeds to sink to the bottom of the container. The dross and liquor are decanted off and the seeds can then be rinsed clean and any adhering material gently rubbed away. Do not allow the process to go beyond the stage at which separation can be achieved - to avoid any detriment to the seeds. Finally wash the seeds with a small amount of dilute detergent and rinse again – this should remove any remaining potential issues such as residual fat which may affect water uptake by the seed or any flesh or skin which may contain germination inhibitors.

 

Assessment

 

Among the ancilliary considerations which may govern the suitability of a sample for collection are:-

a) determination of biological problems such as infestation by insects etc and fungal infection

b) the seed count is usually measured and expressed in two ways - 100grain weight or seeds per unit weight (ie per oz, per lb, per kg) - however it is important, for comparative purposes, to be aware of the status of the assessment of a particular seed lot in terms of whether the data provided is a function of the dry or fresh weight. This is a useful piece of information in that it gives a useful guide to the confirmation of identity, an indication of quality (potential vigour) insofar as it can be assessed against the known average. It also provides information as part of the seed sowing rate calculations and deriving quantities in the purchase of seed. This factor is commonly affected by the nature of the growing season.

c) an approximate field assessment of the viability of the proposed sample.

 

Recording

 

The importance of recording all the relevant activities and conditions with dates and details concerning a seed lot is a sine qua non in the whole process of seed propagation. This provides the basis for the development of efficient and reliable systems for future reference and comparison in developing processes and protocols.

 

Some indication of this detail is presented in Appendix 6.

 

When growing woody plants from seed, at the species level, there is an expectation that the ‘offspring will resemble the parent’ – it is well known that some species will vary considerably (often clinally) and the taxonomic unit (rank) is then decided by the arcane deliberations of the taxonomist – hence the provenance of a seed sample is therefore of some importance