A seedling is young plant saprophytes developing out of plant embryo from a seed up to one metre of height and the term seedling production is the production of seedlings for a certain purpose, especially plantation. The scope of seedling production has been brought by various issues on environmental protection, forest production, tree improvement, ecosystem balance, forest regeneration and many other programs. To fulfill the demand and objective of plantation, there are several techniques and procedures of seedling production developed by experiences and researches on it.
Appropriate site selection, site preparation, quality seed collection, seedlings establishment, storage, protection, management and supply are the components of high seedling yields. Use of efficient machines and strong supervision by experts has wide scope in it.
Mostly seedlings are produced in a nursery either from seed or from vegetative parts. During the plant production, nursery should be established in which beds are prepared for seed sowing and germination of seeds, root-shoot cutting, etc. For very minute seeds, a seed tray for seedling production is prepared filled with different media such as coarse sand, fine soil, forest soil, etc. Sometimes, plastic covered shade house or green house is constructed, where seed trays are placed and seeds are sown in tray for quick germination because there are humidity and temperature controlled. After germination when seedlings gain height or form of 2-4 leaves, they are picked out and transplanted into poly bag or in other type of containers. Overhead shade is provided for root and shoots’ setting and to gain resistance and gradually seedlings become hardened, overhead shade is removed when plants are ready to transplant.
- Seed Sowing: Seeds may be sown by two ways either directly into the pots or it may be sown first in seedbeds or seed trays and the seedling are later picked out into the pots. Generally, Sowing seeds directly into the pots should be used only with fairly large seeds having a germination percentage of more than 40%. Some species that are usually sown areAcacia catechu, Artocarpus lakcocha, Bassia butyracea, Albizea spp., Pinus etc. Methods of direct sowing are also divided into three parts ;
- Broadcast sowing: in this method, the seeds are merely scattered over the surface of the soil. For example, Alnus nepalensis has been successfully established along the lamosangu –charikot road.
- Line sowing: usually strips 30-45cm wide are cleared and hoed depth of 15cm or more. it commonly requires 15-20 times as much seed per hectare as would be needed if the same quantity of seeds was used to raise plants in nursery.
- Patch sowing and sowing in pits: This is sowing of seeds by forming pits and patches in nursery. The development of root of seedlings should be better in pits than patches. This is observed in acacia catechu forest in Pokhara valley. The optimum time for sowing seeds on most sites is during the premonsoon rains as soon as the soil has been sufficiently moisture .In areas where snow can be relied on, sowing before the first snowfall often gives good results, the seed will germinate after the snow melts.
- Cutting: Cuttings can be done differently such as Branch cutting, stem cutting and root shoot cutting.
- Layering: Layering can be done into two ways, i.e., Ground layering and Air layering.
- Grafting: Cleft-graft, veneer-graft, splice/whip and tongue-graft and underbark graft. A scion is used to stock for seedling production.
- Budding: An bud of desired spps is used to stock of inferior species
- Tissue culture: Tissue culture (often called micro propagation) is a special type of a sexual propagation where a very small piece of tissue (shoot apex, leaf section, or even an individual cell) is excised (cut-out) and placed in sterile (aseptic) culture in a test tube, Petri dish or tissue culture container containing a special culture medium. The culture medium contains a gel (agar) with the proper mixture of nutrients, sugars, vitamins and hormones, which causes the plant part to grow at very rapid rates to produce new plantlets. It has been estimated that one chrysanthemum apex placed in tissue culture could produce up to 1,000,000 new plantlets in one year.Thus, tissue culture is used for rapid multiplication of plants.A very specialized laboratory is required for tissue culture.All the procedures are done in a laboratory and special ventilated cabinet that is as sterile as an operating room.
- Different techniques in plant tissue culture may offer certain advantages over traditional methods of propagation, including;
- The production of exact copies of plants that produce particularly good flowers, fruits, or have other desirable traits.
- To quickly produce mature plants.
- The production of multiples of plants in the absence of seeds or necessary pollinators to produce seeds.
- The regeneration of whole plants from plant cells that have been genetically modified.
- The production of plants in sterile containers that allows them to be moved with greatly reduced chances of transmitting diseases, pests, and pathogens.
- The production of plants from seeds that otherwise have very low chances of germinating and growing, i.e., orchids and nepenthes.
- To clean particular plant of viral and other infections and to quickly multiply these plants as ‘cleaned stock’ for horticulture and agriculture.
- Plant tissue culture relies on the fact that many plant cells have the ability to regenerate a whole plant (totipotency). Single cells, plant cells without cell walls (protoplasts), pieces of leaves, or (less commonly) roots can often be used to generate a new plant on culture media given the required nutrients and plant hormones.
Type of Containers
- Container-raised plants (plants in polypots): Raising plant s in polythene containers has become general practice for afforestation in tropical countries, mainly because the rate of survival of seedling is higher especially under unfavorable conditions. They also reduce the rate of failure due to the careless handling by inexperienced labor. Other advantage are that nurseries do not need good soil. The slandered container for raising plants in the nursery is a polythene pots, 3inch*7inch (7.5cm*18cm) lay flat closed at the bottom and made up of transparent 200 gauge polythene with two holes on the side of drain out water. When filled each about 2.5cm in diameter. Black polythene pots are now being used raised seedlings as it is slower to degrade under the effects of sunlight, also prevents the growth of algae within the pots. Especially nurseries above 1500m elevation or where seedlings have to be kept in the pots for more than year, black polythene is preferable.
- Bare-root plants: In this system, seedlings are not grown in separate containers but together in a bed with thousand of plants of others. It is best suited to species with medium to large size seed e.g. pinus spp. The main advantages of bare-root are that they are much easier to transport than plants in containers.
- Large ball-rooted seedling: These are plants of 75-150cm in the nursery for 12 months or longer, and lifted with a ball of soil around their roots 10-15cm in diameter, which is usually wrapped in grass, sacking etc. to keep it moist during transports. This is traditional method in Europe, practically for raising ornamental trees but has been largely replaced growing plants in large containers of plastic and other materials.
- Stump (roots and shoots cuttings): Stumps are prepared by digging up plants from nursery beds, cutting off the stems a few containers above ground level, and shortening and trimming the roots. This method is much easier to transport than container raised plants and less subject than bare root plants.
- Cutting and other vegetative propagated methods: The main use of cutting and other vegetatively propagated materials is when species to raise from seed or seed is not readily available. They also have the advantage of reducing the time needed in the nursery to obtain plants large enough for planting in the field. Another advantage of cuttings is that they are genetically identical with their parent trees so that trees of good form and vigor can be reproduced easily. Cuttings can be classified as: Stem cuttings, Leaf cuttings, Leaf bud cuttings & Root cuttings.
Care and Handling of seedling
From the time you receive your seedlings until they are planted, proper care is vital to maintain their healthy condition. Remember, seedlings are perishable. So, it’s the best to plant them as soon as possible once you have received your order. Here are a few seedling care and handling tips to keep in mind:
- Minimize exposure to wind and sun during transporting seedlings.
- Store in refrigerated location, if available.
- Allow for ventilation around stacked seedling packages.
- Protect seedlings from freezing temperatures.
- Mend any accidental tears in the seedling package with tape to reduce moisture loss.
- Do not water seedlings. Watering will wash away the protective gel applied to the roots at the nursery.
- Protect seedlings from direct sunlight and wind before and during planting.
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