grafting


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grafting,

horticultural practice of uniting parts of two plants so that they grow as one. The scion, or cion, the part grafted onto the stock or rooted part, may be a single bud, as in buddingbudding,
type of grafting in which a plant bud is inserted under the bark of the stock (usually not more than a year old). It is best done when the bark will peel easily and the buds are mature, as in spring, late summer, or early autumn.
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, or a cuttingcutting,
in horticulture, part of a plant stem, leaf, or root cut off and used for producing a new plant. It is a convenient and inexpensive method of propagation, not possible for all plants but used generally for grapes; chrysanthemums; verbenas (stem cuttings); blackberries
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 that has several buds. The stock may be a whole mature plant, such as an apple tree, or it may be a root (usually of a seedling). The most important reason for grafting is to propagate hybridhybrid
, term applied by plant and animal breeders to the offspring of a cross between two different subspecies or species, and by geneticists to the offspring of parents differing in any genetic characteristic (see genetics).
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 plants that do not bear seeds, or plants that do not grow true from seed. It is also used in dwarfing and in tree surgery, to increase the productivity of fruit trees by adding to the number of buds, to adapt a plant to an unfamiliar soil or climate by using the roots of another plant which thrives in that environment, and to combat diseases and pests (e.g., the phylloxeraphylloxera
, small, sap-eating, greenish insect of the genus Phylloxera, closely related to the aphid. Phylloxeras feed on leaves and roots, and many species produce galls on deciduous trees.
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) by using a resistant stock. Grafting does not produce new varieties, since both stock and scion retain their characteristics. Grafting, which was employed in Roman times, is used extensively by nurserymen and other horticulturists. In general, only closely related plants can be grafted successfully. As a rule, the process is begun when the scion is dormant and the stock is just resuming growth. There are many methods of grafting, all of which depend on the closest possible uniting of the cambiumcambium
, thin layer of generative tissue lying between the bark and the wood of a stem, most active in woody plants. The cambium produces new layers of phloem on the outside and of xylem (wood) on the inside, thus increasing the diameter of the stem.
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 layers of both scion and stock.

Bibliography

See R. J. Garner, The Grafter's Handbook (3d ed. 1968).

Grafting

 

in horticulture, the insertion of a scion or bud from one plant onto another plant, known as the stock. The cambiums of the stock and the scion are placed close together, and, as a result, they concresce completely, forming a single, normally functioning plant.

Grafting is one of the most important methods of vegetative propagation for fruit-bearing species. It is also used to preserve the varietal characteristics of perennial plants; to replace a stock that is not adapted to existing soil and climatic conditions; and to replace a scion with one that is more economically valuable, winter-hardy, and disease- and pest-resistant. In addition, grafting may be used to induce fruit production, to mend plants with injured barks, and to form ornamental creeping and dwarf plants.

There are several hundred methods of grafting, but only about ten to 15 are used in commercial production. Budding, grafting proper, ring grafting, inarchment (grafting by approach), and seedling-inarchment are commonly used for propagating fruit species. In herbaceous plants parts of fruits, tubers, and bulbs may be inserted into the stock, or the embryos of one seed may be transferred to another. Winter grafting is done indoors during vegetative rest, usually in the second half of the winter. Spring grafting is performed from March through June, and summer grafting from June through September. All grafting under the bark of the stock, including budding, is done when there is cambial activity. Other methods are performed at earlier periods.

Budding is the most common and simplest method of grafting. It is more productive than other methods, having a higher percentage of successful unions and requiring only a small number of cuttings. Spring budding uses buds from the previous year’s cuttings that unfold within 15 to 20 days. This form of propagation is used mainly for fast-growing drupaceous species in the south, where there is a long vegetative period. For summer budding, cuttings of the current season are used, whose buds remain dormant until the following spring. Grafting is completed 50 to 60 days before the onset of the cold season: in the northern zone by August 5, in the Central European USSR by August 15, and in the south by September 15.

Stocks for budding are maintained in a state of high cambial activity by means of watering and hilling. This helps the bark separate readily from the wood. Mature cuttings, which are 30 to 40 cm long and no less than 6 mm thick, are obtained from fruit trees on the day they are to be grafted or the night before. Well-developed, mature buds from the middle part of the cuttings are used. Budding involves several operations: slicing off a sliver of bark with a bud, making a T-shaped incision in the bark of the stock near the root collar (5–7 cm from the soil surface), inserting the sliver in the incision, and binding of the site of budding with linden bast, polychlorvinyl film, flax fiber, or some other material. The bud may be cut off with or without a thin layer of wood. Two buds are sometimes used to increase the number or successful unions if the scion variety has buds that unfold with difficulty. After budding is completed, the soil is loosened and the plants are hilled if necessary. At the time of inspection, after ten to 15 days, plants with dead buds are re-grafted, and those with successful unions have their bindings loosened.

Grafting proper includes the following general types: whip grafting, veneer grafting, side grafting, wedge grafting, cleft grafting, bark grafting, and bridge grafting. Whip grafting (simple or improved) is possible when the stock and scion are of equal diameter. It is used in plant nurseries and for regrafting one- and two-year-old branches of adult trees in orchards. With simple whip grafting, equal-length oblique cuts are made on the upper end of the stock and the lower end of the scion. With improved whip grafting, longitudinal notches are made on the oblique cuts, forming little “tongues.” The scion and stock are then joined together, and the site of joining is bound as in budding and covered with grafting wax. Veneer grafting is used when the stock is thicker than the scion. The stock is cut down to form a small stump, to which is applied a scion whose sliced surface exactly matches in length and width the vertical cut on the stock. Side grafting is performed on the lower part of the stock, which is cut down to form a tenon 10 to 15 cm long. A lateral notch is made in the stock, into which the cutting, sliced to form a double-faceted wedge, is inserted.

In wedge grafting the stock is cut crosswise, and a wedge-shaped piece is cut out of the wood laterally. The lower end of the cutting, sharpened on two sides into a wedge, is then inserted into the stock. Cleft grafting, which is performed on thick stocks, is commonly used for regrafting fruit trees. The stock, in the form of a stump, is split vertically and cuttings that have two recesses or are sharpened into wedges are inserted from two sides. With bark grafting, the stock is cut down to a stump and one or more cuts to the cambial layer are made on the side; into these are inserted the cuttings, which are cut slantwise or with a recess. Another type of bark grafting involves removing a thin strip of bark, sometimes with a layer of wood, from the end of the stock, which is cut down to form a tenon. The bark is longitudinally cut apart in the lower part, and a graft with a slanting cut is inserted. Bridge grafting is used for trees whose bark has been severely damaged by rodents or burns. A scion is placed over the wound.

Ring grafting is used in the spring, summer, and early autumn to propagate the walnut, pecan, chestnut, and mulberry. A ring of bark is removed from the stock at the graft site, and a similarly sized ring of bark with a bud from the scion is inserted.

REFERENCES

Vanicek, K. H. Uluchshenie drevesnykh nasazhdenii privivkoi. Moscow, 1960. (Translated from German.)
Biriukov, M. P. Privivka plodovykh rastenii. Sverdlovsk, 1962.
Garner, R. Rukowdstvo po privivke plodovykh kul’ tur. Moscow, 1962. (Translated from English.)
Stepanov, S. N. Plodovyi Pitomnik. Moscow, 1963.

M. D. KUZNETSOV

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