Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion while the lower part is called the rootstock. The success of this joining requires that the vascular tissues grow together and such joining is called inosculation. The technique is most commonly used in asexual propagation of commercially grown plants for the horticultural and agricultural trades. In most cases, one plant is selected for its roots and this is called the stock or rootstock. The other plant is selected for its stems, leaves, flowers, or fruits and is called the scion or coin. Joints formed by grafting are not as strong as naturally formed joints, so a physical weak point often still occurs at the graft because only the newly formed tissues inosculate with each other. The existing structural tissue of the stock plant does not fuse.
Advantages
Precocity. The ability to induce fruitfulness without the need for completing the juvenile phase. Juvenility is the natural state through which a seedling plant must pass before it can become reproductive In most fruiting trees, juvenility may last between 5 and 9 years, but in some tropical fruits example, mangesteen, juvenility may be prolonged for up to 15 years. Grafting of mature scions onto rootstocks can result in fruiting in as little as two years
Dwarfing. To induce dwarfing or cold tolerance or other characteristics to the scion Most apple trees in modem orchards are grafted on to dwarf or semi-dwarf trees planted at high density They provide more fruit per unit of land of higher quality and reduce the danger of accidents by harvest crews working on ladders. Care must be taken when planting dwarf or semi-dwarf trees. If such a tree is planted with the graft below the soil, then the scion portion can also grow roots and the tree will still grow to its standard size.
Ease of propagation. Because the scion is difficult to propagate vegetatively by other means, such as by cuttings In this case cuttings of an easily Tooted plant are used to provide a rootstock In some cases, the scion may be easily propagated, but grafting may still be used because it is commercially the most cost-effective way of raising a particular type of plant.
Hybrid breeding. Speed maturity of hybrids in fruit tree breeding programs. Hybrid seedlings may take ten or mor years to flower and fruit on their own roots. Grafting can reduce the time to flowering and shorten the breeding program.
Hardiness.cBecause the scion has weak roots or the roots of the stock plants are tolerant of difficult conditions. Many Western Australian plants are sensitive to dieback on heavy soils, common in urban gardens and are grafted onto hardier eastern Australian relatives. Grevilleas and eucalypts are examples.
Sturdiness. To provide a strong, tall trunk for certain ornamental shrubs and trees. In these cases, a graft is made at a desired height on a stock plant with a strong stem. This is used to raise standard roses, which are rose bushes on a high stem, and it is also used for some ornamental trees, such as certain weeping cherries.
Disease pest resistance. In areas where soil-borne pests or pathogens would prevent the successful planting of the desired cultivar. The use of Dest disease tolerant rootstocks allow tire production iom the cultivar that would be otherwise unsuccessful. A major example is the use of rootstocks in combating Phylloxera.
Pollen source. To provide pollenizers. For example, in tightly planted or badly planned apple orchards of a single variety, limbs of crab apple maybe grafted at regularly spaced intervals onto trees down rows, say every fourth tree This takes care of pollen needs at blossom time.
Repair. To repair damage to the trunk of a tree that would prohibit nutrient flow, such as stripping of the bark by rodents that completely girdles the trunk. In this case a bridge graft may be used to connect tissues receiving flow from the roots to tissues above the damage that have been severed from the flow. Where a water sprout, basal shoot or sapling of the same species is growing nearby any of these can be grafted to the area above the damage by a method called inarch grafting. These alternatives to scions must be of the correct length to span the gap of the wound.
Changing cultivars To change the cultivar in a fruit orchard to a more profitable cultivar called top working. It may be faster to graft a new cultivar onto existing limbs of established trees than to replant an entire orchard.
Genetic consistency. Apples are notorious for their genetic variability even differing in multiple characteristics such as size color and flavor of fruits located on the same tree In the commercial farming industry, consistency is maintained by grafting a scion with desired fruit traits onto a hardy plant.