Explanation of the diagram
Grafting (including budding) is a process by which a portion of the shoot system or root system of the same or different plants, brought into intimate contact, unite and grow together anatomically, and interact physiologically as a single functional unit (whole plant).
Scion is the upper of the two or more pieces brought into contact during the process of grafting, which grows into all or part of the shoot system.
Stock is the lowest of the pieces brought into contact during the process of grafting, which develops into the root system and in some cases the lower portion of the shoot system below the graft union. Similar terms are rootstock and understock.
In the case of natural grafting, described in the section on Natural and Human History of Grafting and Budding, the parts that come into contact are shoots or roots of the same or adjacent intact plant, so that the terms stock and scion become somewhat ambiguous. For example, when the trunks or limbs of two adjacent trees come into contact and become grafted together, it is rather meaningless to use the horticultural terms stock and scion.
In the case of deliberate (horticultural) grafting, the scion is usually detached from the scion donor plant and placed into contact with an intact stock plant. This is known as detached scion grafting. Approach and Inarch grafting are exceptions in that they are deliberate grafting methods in which both stock and scion donor plants are intact (on their own root systems) during the period of graft union formation.
Budding (bud grafting) refers to any grafting technique in which the scion consists of only a single bud and associated stem tissue. By contrast, the term "grafting" is usually used to refer to methods that involve a multibud scion.
Double working refers to a three part plant with two graft unions, constructed from a stock and a scion separated by an intermediate shoot piece known as an interstock.
Top working refers to the practice of grafting new scions high up in the canopy of an established tree, to change over to a new (fruit) variety, or to insert a pollinizer branch, etc. In many cases topworking is performed on a tree that was previously grafted (e.g. in the case of apples, top working might be performed on a tree that was originally grafted to a dwarfing rootstock). In such cases the topworked tree consists of at least three genotypes, so it could, technically (but not commonly), be referred to as doubleworking- new scions / interstock (original scion) / rootstock.
High working is similar to topworking, but the graft is usually performed earlier, during the nursery production phase of the plant's life span, in order to create a special growth form. For example a weeping cultivar of flowering cherry might be highworked onto a non-weeping cherry understock to create a weeping canopy several feet high on an upright (non weeping) trunk.
Conventional Scion/Interstock/Stock Nomenclature: It is a common practice, which you will see in other sections of this course, to refer to the names of the scion and stock and interstock varieties involved in a particular graft combination in the order: scion/stock or scion/interstock/stock. E.g. Macintosh/MM111 refers to the apple variety Macintosh grafted onto a MM111 rootstock, whereas Macintosh/M9/MM111 would refer to a double worked tree consisting of a Macintosh scion, an M9 interstock and a MM111 rootstock.
As you continue with lecture sections following this one, find one or more specific examples (crops and applications) of placement types B through E.
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