Asexual Propagation of crops:
Asexual or vegetative propagation involves the growing of new plants from the vegetative parts of the parent plants.
Plants that can be propagated by vegetative means are:
1. Plants that do not produce seeds.
2. Plants that produce seeds, but the seeds are not viable for planting.
3. Plants that are easier to propagate by vegetative means, instead of using seeds which may take a longer period.
Asexual or vegetative propagation can be divided into four groups namely, cutting, budding, grafting and layering.
When parts of a plant are cut into portions and planted to produce new plants, such cut portions are called cuttings.
Cuttings may come from stems or leaves depending on the type of plant being propagated. Plants whose stems produce roots fairly readily are propagated by stem cuttings.
Hardwood cuttings are prepared from stems of perennial plants, taken from the previous season’s growth. These cuttings may be from 15-30cm long depending on varieties. Examples of plants propagated by cuttings are cassava stem (Fig. 16.18), hibiscus, sugar cane, cocoa, kola and coffee while soft wood cutting is obtained from sweet potato.
Precautions to be taken during cutting
i. Cut from mature stems
ii. Make sure that cutting have axillary buds.
iii. Use sharp cutlass for the cuttings
Suckers are shoots which normally develop from the base of the parent plant. Many crops can be propagated by suckers and examples of such crops include banana (Fig. 16.19), plantain and pineapple. Suckers usually contain large quantities of food reserves and can survive for some time before being planted.
Layering is used to produce new plants of crops like cocoa, kola and coffee. A branch or shoot growing near to the ground is bent over so that one or two of the nodes touch the ground. A slit is made on the node, and the branch pegged to secure it in position. The node is covered with soil. Adventitious roots grow out from the node. When the roots are well established, the stem is severed from the parent plant and transplanted to the field to become a new plant.
The diagram showing layering.
Precautions to be taken during layering
i. Ensure that one or two nodes touch the ground
ii. Make a slit in the node to case the propagation of adventitious roots
iii. Peg the bent shoot to secure it in position
iv. Cover the node with moist soil
Budding is a skilled technique used when plants do not grow easily from cuttings. A bud is cut from a matured branch (usually two years old).
Attached to the bud is a flat, shield-shaped piece of stem. The stem piece and bud is called the scion. An inverted T-shaped cut is made in the bark of another tree of a desirable characteristic called the stock and the edges of the cut are turned back to expose the cambium. The scion is inserted into the stock and then the two are bound into position and the joint made water-proof e.g. by polythylene tape or raffia, leaving the actual bud exposed. This prevents the bud from being scalded by the sun and also prevents bacteria and water from entering the wood before it heals. If the bud unites successfully with the stock, it begins to develop into a new shoot after about three weeks. At this stage, the wrapping is removed.
The bud eventually produces a shoot system and when well developed, the portion of stock above the bud is removed with a sharp knife or secateurs. The cut may be tarred or covered with paint in order to prevent the entry of disease. All branches below the scion should be carefully removed. When fully developed, the budded plant is carefully transplanted to its permanent site. Crops normally propagated by budding include citrus especially, cocoa and rubber. The processes involved in budding.
Grafting is closely related to budding and is a method of vegetative propagation which involves the application of a whole shoot or stem (the scion) into another plant (the stock). Grafting brings into close contact the vascular cambia of both the scion and the stock. As in budding, both the scion and the stock must be closely related to avoid incompatibility, which could result in the breaking of the scion from the stock at later date. The basic grafting operation is similar to that of budding. Types of grafting include the cleft, saddle, side and whip and the tongue. Crops easily propagated by grafting is the citrus spp. The processes involved in grafting
Precautions to be taken during grafting
i. Take care not to injure the cambia of scion and stock
ii. Choose scion and stock of almost the same size and relations
iii. All side shoot below the point of union of scion and stock must be cut off
iv. The tape should be tied from below upwards to prevent rain damage to the grafted site.
Advantages of vegetative propagation
i. Plants that do not produce seeds can be propagated e.g. navel orange
ii. It enables plants such as yam with low seed germination to be propagated
iii. There is no change in quality, growth habit and possibly yield, when plants are propagated by vegetative means.
iv. Plants tend to mature and bear fruits early.
v. The quality of one plant can be blended with the quality of another plant. E.g a particular plant may be high yielding, but highly susceptible to certain diseases. In this case, the scion of such a plant can be grafted with a disease resistant root stock, that may be low yielding, but of the same species.
Disadvantages of vegetative propagation
i. Budding and grafting need special skills
ii. Easy transfer of diseases is possible, if propagation method used is not carried out efficiently.
iii. One variety of a plant can be produced indefinitely.
iv. Plants produced are not vigorous and may not live long.
21. MILKING MACHINE
22. SIMPLE FARM TOOLS
23. AGRICULTURAL MECHANIZATION
24. THE CONCEPT OF MECHANIZATION
25. PROBLEMS OF MECHANIZATION
26. SURVEYING AND PLANNING OF FARMSTEAD
27. IMPORTANCE OF FARM SURVEY
28. SURVEY EQUIPMENT