What is Grafting in Plants?
In crop farming or crop agriculture, grafting is most commonly referred to as an artificial, vegetative method of plant propagation. However, as a technique or procedure, it has many other uses. The term is also applied in animals and in humans as in skin grafting.
Plant grafting is a procedure in which parts of plants are joined together with the ultimate intention of making them unite and continue growing as one plant. A grafted plant, therefore, is a composite of parts derived from two or more plants.
Grafting generally applies to the dicots and to the gymnosperms because of the presence of a continuous vascular cambium between the xylem and the phloem. But in the monocots that have no vascular cambium, successful grafts are rare and difficult.
Two terms are common in grafting: rootstock and scion. These terms are always used in reference to what is grafting rather than in other methods of plant propagation.
The rootstock, also called understock or simply stock, is the lower part having roots and usually consists also of a stem that is to become the lowermost part of the shoot of the grafted plant. The rootstock provides anchorage as well as support to the upper parts of the plant.
The scion, or cion, is the upper part that is joined to the rootstock and is the main component of the plant shoot when the plant is fully developed. It usually consists of the primary stem (trunk) and branches except the portion that belongs to the rootstock. The scion determines the characteristics of the plant as to leaves, flowers, fruits and seeds, and thus needs to be chosen with care.
In plant propagation by grafting, the scion to be joined to the rootstock consists of a portion of stem, usually small twigs, with multiple number of buds. The apical bud is usually included, but other species can be readily grafted using scions with only axillary buds. Where the scion consists of a single bud, the grafting method is especially termed budding.
1. Plant Propagation. In some plant species and varieties, grafting is the better method of mass propagation where uniformity in plant characteristics is desired. This is so in plants in which other asexual methods are ineffective. It is also employed where other methods do not allow the production of a big number of planting materials in the shortest time possible. While budding has the potential of producing more clones from a single mother plant because scions with a single bud are used, the growth of the scion is slow and it will take more time to produce the right sizes of budded plants for outplanting. Plant cuttings generally exhibit the same growth rate.
2. Producing Composite Plants with Rootstocks Having Special Characteristics. Desirable scions can be grafted on rootstocks that are adapted to certain conditions such as heavy, wet, or dry soils, or resistant to soilborne pests and diseases. There are rootstocks also that will enhance the vigor or induce dwarfing of the grafted plant. In citrus, some rootstocks favor the production of fruits with better size and quality (Hartmann and Kester 1975).
In general, the compatibility of the rootstock and scion that leads to successful union depends on how close they are in their taxonomic classification. The possibility of a successful union is more ensured among plants within the same species. But intergeneric grafting is now widely practiced in plant propagation to take advantage of more adapted and disease resistant rootstocks. Examples are the eggplant (Solanum melongena) and upo or bottle gourd (Lagenaria siceraria), as rootstocks, with tomato (Lycopersicon esculentum) and watermelon (Citrullus lanatus), respectively. Eggplant and tomato belong to the family Solanaceae while bottle gourd and watermelon are both members of the family Cucurbitaceae.
Old jokes in relation to what is grafting: (1) Q: Can bamboo and banana be grafted? Ans: Yes, as in banana cue (a bamboo stick is used to pierce a fried sweetened plantain for easy handling). (2) Q: Can bamboo and coconut be grafted? Ans: Yes, to produce tuba or coconut toddy (a segment of bamboo culm is traditionally used as a container into which the coconut inflorescence that is sliced daily is inserted to collect the sweet coconut sap that exudes).
3. Conversion of Adult Trees to Desirable Types. Large, mature trees can be converted to another species or variety having desirable characteristics by topworking (or top-grafting). Regrafting of the top with scions obtained from “carabao” mango has been applied in mango trees that have started fruiting but found to belong to an inferior variety (click here to read). Intervarietal conversion is also resorted in association with the rejuvenation of old and unproductive coffee. Likewise, some dioecious trees can be converted from male to female to make them productive or from female to male to ensure supply of pollen for the entire orchard.
4. Producing Botanical Curiosities. Special types of plants can be produced by grafting two or more scions with different characteristics on the same rootstock. For example, a mango tree can be topworked in a manner that different branches will bear different fruit types. A croton or san francisco (Codiaeum variegatum) can also have a foliage with different leaf types and variegation.
5. Artistic Enhancement. In bonsai, a tree that lacks an essential branch at certain part of the trunk, or branch, can have one by grafting thereon a scion, usually by side or approach grafting. This is a strategy applied in creating fine bonsai trees that requires a substantial understanding on what is grafting and its various techniques.
6. Repairing Damaged Trees. Tree plants with damaged portions of the trunk are common where there are goats and carabaos. Occasionally, damage to trunks and branches is also caused by fire, insects, diseases, mechanical impact, and mishandling of tools. These damaged parts can be repaired and saved by inarching or bridge-grafting.
7. Additional Anchorage and Support. In places that are prone to strong winds, it is advantageous if tree crops are anchored well to the ground. Lodging can be prevented or minimized by producing tripods or multiple-trunk trees by inarching. Similarly, weak branches and split trunks can be prevented from breaking by brace grafting.
8. What is Grafting: Indexing for Virus Diseases. Some plants have strong tolerance to virus diseases so that even if the disease is present, they exhibit little or no symptom. To identify plants that may carry the virus, scions or buds from such plants are grafted onto a healthy, susceptible indicator plant. If the suspected plant from which the scion or bud is derived is infected, the virus will be transmitted and the indicator plant will show the symptoms of the disease (Hartmann and Kester 1975).
HARTMANN HT, KESTER DE. 1975. Plant Propagation: Principles and Practices. 3rd ed. New Jersey: Prentice Hall Inc. 662 p.
(Ben G. Bareja May 2011)