COLLECTION OF PLANT PROPAGULES
Responsible, safe and efficient harvesting methodology can significantly reduce the impact that the collection process has on the wild plant. As much as possible, the collection event should be planned out beforehand and not left to arbitrary decisions in the field. It would not be of benefit and in fact be potentially detrimental to you and/or the plant to have unnecessary visitations or collections made due to improper planning.
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Seed quality is primarily dependent upon the methodology of the seed collector and the post-harvest handling of the collected material. Improper harvesting and cleaning protocols may cause unwanted damage to the collected seeds. Seed collection trips should coincide with the plant’s natural seed production cycle, concentrating particularly during the period of maturation just before natural seed dispersal. Seeds are usually considered mature when it can be removed from the plant without impairing the seed’s germination. This usually indicates that the seed has reached its maximum dry weight and no further increase will occur. A seed is a miniature plant in an arrested state of development and most seeds contain a built-in food supply (orchid seed is an exception). Harvesting prematurely ripened fruits or immature seed usually result in plant embryos that are insufficiently developed, thin, underweight, shriveled, low quality and short-lived. If harvesting is delayed, the fruits may dehisce, fall to the ground, or be eaten or carried off by birds or animals. Seed viability of tree and shrub species varies considerably from year to year, from locality to locality, and from plant to plant.
Different types of fruits are classified by the nature and structure of the ovary wall and their ability to split apart when ripe (dehiscence), as well as the manner in which this occurs, and the way in which the seed is attached to the ovary.
Dry dehiscent - Fruit capsules dehisce (burst open) or “shatter” at maturity to release single, dry seeds. To avoid seed losses, such fruits from such plants should be harvested before they are fully ripe. A problem of dry dehiscent seeds that occur on a single plant is that they may not develop uniformly and at harvest a portion of the seeds will be immature. Dry dehiscent type fruits and capsules include follicles, pods, capsules, siliques, cones of conifers, some grasses (caryopses) and Compositate plants (achenes).
Dry indehiscent – Fruits do not dehisce nor release their seed immediately upon maturity. Commonly found in agronomic plants grown for their seeds, such as corn, beans, and wheat. Some species tend to lodge (stems bend over) thereby necessitating the stems to be cut, dried and cured prior to harvesting. Timing of harvest is dependent upon when and how normally dispersed (e.g. wind, animals, insects, etc.).
Fleshy fruits – Seeds are produced in fleshy fruits. Many times, dispersal is enhanced by animals ingesting the fruits and disseminating the seeds through their digestive tract. Pick fruits when ripe and if possible, avoid ones that have fallen to the ground. Overly ripe fruit and fruit that have dropped tend to have increased problems with microorganism growth. Remove the flesh off of the seeds before storing. If it is left on and allowed to dry, it can be hard to remove and may contribute to dormancy problems.
It is also important to know if the seeds you are collecting are recalcitrant (desiccation intolerant) or orthodox (desiccation tolerant).
Recalcitrant seeds cannot withstand any drying, have some seed coats adapted to prevent excessive water loss while others have no such adaption and are prone to rapid water loss post harvest. In fleshy fruits, high seed moisture can be maintained by keeping the fruit intact. Their individual seeds can be stored in impermeable plastic bags, but must be aerated by opening the bag intermittently to compensate for the restrictive gas exchange environment. While in the field and during transport, insulate against heat and temperature extremes. Try to maintain a temperature as close to ambient as possible.
In mature fruit, indicate if picked off the ground or parent plant. Try not to collect from the ground if possible, unless it is known that they have recently fallen.
In general, the dessication tolerance of orthodox seed varies throughout its development. They tend to be intolerant of drying during early development and become more tolerant as the seeds mature. If the fruits are immature, leave the seeds within the fruit. Treat in the same manner as recalcitrant seeds.
If you are unable to submit your seed samples to a storage or propagation facility right after a collection is made, simple cleaning, processing, and storage steps should be initiated to maintain the quality of the seeds.
1) Low humidity is important during drying and curing to minimize the growth of microorganisms.
2) Drying temperatures should not exceed 110oF (43°C). If the seeds are wet, 90°F (32°C) is better. Too rapid drying can cause shrinkage and cracking and can sometimes produce abnormally hard seed coats.
3) Seeds from ripe fleshy fruits are usually scooped out, washed and dried, but may require additional cleaning through extended soaking, mechanical means (specialized machines), or washing through screens.
4) Extended soaking- macerated fruits are placed in a container with water and allowed to soak for a few days in the refrigerator or no warmer than 70oF (21°C). Stir occasionally. Usually, the good seeds will sink to the bottom and the lighter pulp and empty seeds will remain on the top.
5) Cleaned and dried mature seeds can be temporarily stored in closed containers in the refrigerator.
Unlike flowering plants, ferns reproduce by means of spores. These spores are very small and can be hard to see with the naked eye unless in large quantities. Making a successful collection of spores takes some practice and a little luck. The two most important factors to consider when attempting spore collection are: maturity of spores and contamination from weedy fern spores.
Most fern species tend to develop and release spores on a seasonal basis, so timing of collection is a critical factor. Mature spores and sporangia will often be dark in color and uniform in texture, although it is best to look for spore maturity characteristics on a species by species basis. This is because fern spores can range in color from green to black, or even yellow. A magnifying device can be utilized to determine spore maturity and texture of sporangium. If sporangia feel or look as if they have a rough texture, it is likely that they sporangia are uncoiled and the spores have already been released. Often times sporangia and spores are encapsulated within an indusium, or covering. Each species is different but most species will shed their indusium close to optimal spore maturity, which can be used as indicator for proper collection timing.
Collection of vegetative material from ferns should be done conservatively because plants can be easily damage if over-collected. One fertile frond can yield hundreds of thousands of spores, so large amounts of material need not be collected for successful propagation. Upon collection, fern fronds should be rinsed or sprayed down with water to wash off any weedy fern spores. After spraying down with water collected material should be placed in a sealed plastic bag to maintain a moist environment until material can be processed in laboratory setting. Maintaining a moist environment is crucial during transportation because if material is allowed to dry out spores will be released in the collection bag, which will make processing very difficult. Material should be kept in this moist condition for a day or two at the most. However, the quicker the collected materials can be processed, the better.
Processing of collected fern material should be done in an environment with as few contaminants as possible. Microscopic spores, from ferns and mold, can be floating in the air all around you, which can lead to contamination. Collected material should be placed in a folded paper packet and kept in dry conditions for 24 hours. With in this period of time the frond or pinnae will dry out, and this will in turn trigger the sporangia to uncoil and release spores. After approximately 24 hours of drying, all mature spores should be released from the collected material. A paint brush can be used to brush the spores from the surface of the paper packet. Most likely a combination of spores, sporangia, and other vegetative debris will be a resulting product. This can then be sifted with a #230, 63 micron, sieve to achieve pure spores.
Pictures below are examples of three stages of fern spore maturity of Chirstella sp.
Figure 1 is an example of immature spores which have a pale green color and the indusium is still intact to the sporangium. These spores are far too immature to collect, wait a week or more, depending on the species, and you might have a better chance of finding mature spores.
Figure 2 is an example of sporangia that have already released their spores. Note the coarse texture and light brown color. Also notice that the indusium is no longer attached to the sporangia. This material is far past optimal collecting condition. Collection of this quality of material will result in many sporangium and very few spores, your better of waiting until next season for more mature material.
Figure 3 is an example of a fern that has just reached optimal spore maturity. Some of the sporangia near the tip of the pinnae have already begun to release spores, but majority of the sporangia are at the right stage of maturity. Note the dark brown/black color of the spores and smooth texture of the sporangia. Also, notice the indusium is still attached yet beginning to unhinge from the sporangia. Upon collecting and processing several pinnae, this fern yielded several tens of thousands of spores ready for propagation.
Fern fronds should be kept in plastic bags and not allowed to dry out during transport. If immediate delivery to the laboratory is difficult, place frond between 2 sheets of paper and allow to air dry flat within a plastic bag propped open. Spores will fall off frond as it dries. Seal the bag shut when completely dry and maintain a flat position to keep the spores on the paper surface.
Plants possess the ability to go through a process of dedifferentiation and regeneration into new root and/or shoot systems, and any vegetative part of the plant can potentially be used as a cutting. These plant processes make vegetative propagation possible and in fact, it is used extensively with dicotyledonous plants and a few monocots. Listed here are various types of cuttings that can be made and the methods for preparing and caring for them will be discussed.
Successful propagation of vegetative material is dependent upon many different factors such as the vigor of the parent, the collection date and even the environmental conditions at the time of collection. Correct handling of vegetative material is also important.
1. Vegetative materials deteriorate quickly post harvest and quick transfer from field to the propagative facility is imperative to ensure maximum viability.
2. Additional care must be taken during transport since they are easily mechanically damaged and sensitive to excessive heat.
Stem cuttings are the most common type of explants used for propagation, where shoot segments containing the apical and/or axillary meristems are collected.
Stem cuttings are best gathered in the early part of the day and should be kept moist, cool, and turgid at all times by wrapping in damp, clean wrapping material or by placing in a plastic bag, and keeping the cuttings out of the sun. Soaking the cutting material or cuttings in water for prolonged periods to keep them fresh is not recommended. The propagating material should be taken from healthy, normal and moderately vigorous plants growing under the plant’s natural light requirements. Cuttings should not be selected from extremely weak growth with abnormally long or small internodes or from interior shoots, as well as vigorous abnormally thick, or heavy ones. Avoid taking cuttings from plants that show symptoms of mineral nutrient deficiency, disease, and insect infestations. Avoid material with flower buds if possible, but take cuttings preferably from the upper part of the plant. While terminal parts of the stem are usually the best for cuttings, a long cutting can be divided into sections and used for propagation.
Stem cuttings are usually divided into 4 categories, with generally distinguishable characteristics that determine each category. Characteristics such as color of the leaves and stems, firmness of the wood, and stage of bud development can be used to assess the suitability of potential cutting material.
1) Hardwood – Hardwood cuttings are the least expensive and one of the easiest method of vegetative propagation. They are easy to prepare, not readily perishable and may be shipped safely over long distances if necessary.
Hardwood cuttings vary considerably in length from 4 – 30 inches. At least 2 nodes are included in the cutting: the basal cut is usually just below a node and the top cut ½ to 1 inch above a node. The diameter of the cutting may range from ¼ inch to 1 or even 2 inches depending upon the species. The three different types of cuttings that can be prepared are the straight, heel and mallet. A straight cutting is the most commonly used stem cutting. Mallet and heel cuttings are used for plants that might otherwise be more difficult to root. For the heel cutting, a small section of older wood is included at the base of the cutting. For the mallet cutting, an entire section of older stem wood is included.
Hardwood cuttings from deciduous and broadleaf evergreen plants are taken from dormant, mature stems, with no obvious signs of active growth. The cuttings should have an ample supply of stored foods to nourish the developing roots and shoots until the new plant becomes self sustaining. The tip portions of a shoot are usually low in stored foods and are discarded. Central and basal parts make the best cuttings. Where it is difficult to distinguish between the top and base of the cuttings, it is advisable to make one of the cuts at a slant rather than at right angles.
2) Semi-hardwood – Semi-hardwood cuttings are usually taken from new shoots just after a flush of growth has taken place and the wood is partially matured. The cuttings range from 3-6 inches in length and leaves are retained at the terminal end.
3) Softwood (greenwood) – Softwood cuttings are prepared from soft, succulent new growth of deciduous or evergreen species. Shoots are suitable for softwood cuttings when they possess some degree of flexibility, but are mature enough that they can be snapped easily when bent sharply. Some of the best cutting material is the lateral or side branches of the stock plant. Software cuttings are usually 3-5 inches long with two or more nodes, with the basal cut usually made just below the node. Softwood cuttings generally root easier and quicker than the other types but require more attention and equipment.
4) Herbaceous – Herbaceous cuttings are made from succulent, herbaceous plants and are usually 3-5 inches long with leaves usually retained on the terminal end.
New plants can be initiated through leaf cuttings in some species. In the propagation through leaf cuttings, adventitious roots and shoots must be regenerated, usually from the base of a leaf blade, or leaf blade and petiole. The original leaf does not persist or become part of the new plant.
Leaf – Bud Cuttings
Leaf-bud cuttings, sometimes referred to single-node cuttings, consist of a leaf blade, petiole, and a short piece of the stem with the attached axillary bud. In some cases where shoots can not be obtained through leaf cuttings, leaf-bud cuttings can be used to obtain shoots from the axillary bud at the base of the petiole. This method is useful when plant material is hard to obtain or scarce, and has to potential to produce at least twice as many plants as stem cuttings.
When lateral shoots are not available, such as palms and other monocots, it is sometimes possible to produce vegetative shoots from root cuttings. Roots are often considered to be more juvenile in age than most of the tree, with the most juvenile material being closest to the trunk/main stem, having a greater propensity to form shoots. Sprouts arising naturally from the roots of trees generally are juvenile in form and are great sources for root cutting material. Also, almost any plant that suckers in nature is a good candidate for production by root cuttings. Collect roots just before the new growth starts, when the roots are well supplied with stored foods. Root cuttings can be transported/stored for a short while in a moist sterile medium, such as peat moss.
Root cuttings must initiate a new shoot system from an adventitious bud as well as an extension of the existing root piece.
Flowerbuds and Inflorescences
A few plant species have been known to form adventitious shoots from immature flower buds and flower inflorescences. Some flowering shoots contain vegetative buds that do not develop but remain dormant. Sometimes the dormancy can be broken to produce juvenile vegetative shoots.