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Definitions of Terms, Tools, Reasons and Limitations of Grafting
Definitions of terms
Bark: all tissues lying outward from the vascular cambium.
Callus: mass of parenchyma cells, that develops from and around wounded plant tissues. It occurs at the conjunction of a graft union, arising from the living cells of  the scion and the rootstock. The production and interlocking of these cells constitute one of the important steps in callus bridge formation between the scion and the rootstock in a successful graft.
Cambium: is a thin  layer of meristematic cells located between the bark (periderm, cortex and phloem) and the wood (xylem). Its cells are in continues division originating new cells. For a successful graft union, its really important that the cambium of the scion be in close contact with the cambium of the rootstock. 
Compatible: plants parts that are capable of forming a permanent union when grafted together.
Graft: a finished plant that comes from  joining a scion and a rootstock. 
Grafting: is a technique used to connect two parts of different plants by bringing the plant tissue together in such a manner  that they will unite and grow together.
Incompatible: plants whose parts will not form a permanent union when grafted together.
Interstock: an intermediate plant part that is compatible with both the scion and the rootstock. Used in cases where the scion and the rootstock are not directly compatible with each other or where additional dwarfing and cold or disease resistance is desired.
Scion: is the upper portion of the graft that will provide the shoot system.
It should be of a desired cultivar and disease free. For example, Picea pungens 'Hoopsii' (Hoops Blue Spruce) side-veneer grafted on P. abies (Norway Spruce).
Scion rooting: the development of roots from the scion after grafting.
Rootstock/ understoock: the lower part of the graft , which develops into the root system of the grafted plant. It may be a seedling, a rooted cutting, or a layered or micropropagated plant. e.g.  Picea abies (Norway Spruce) to receive the P. pungens 'Hoopsii' (Hoops Blue Spruce) scion.
Union: point where the scion and rootstock are joined.
 
Tools  for Grafting
Knives: Grafting knives are specially designed for this purposes. The blade is beveled only in one side and they should be kept razor sharp so they will cut smoothly. They are available in either left or right hand.
Pruning and Lopping Shears: they should be the scissors or the sliding blade type rather than the blade and anvil type. If the blade and anvil pruner is used to harvest scion wood , plant tissue will be crush. as with knives, pruning and lopping shears should be kept sharp to give clean, close cuts.
Grafting Strip: a rubber strip used to hold scion in place until knitting has occurred.
Reasons for Grafting Plants
 Grafting is used for many different purposes:
  • To perpetuate clones that cannot be maintained or economically propagated by other propagation methods.
  • To obtain the benefits of certain rootstocks.
  • To produce a crop of certain plants in a short amount of time.
  • To obtain special forms of plants growth.
  • Changing cultivars of established plants.
  • To repair damaged parts of trees.
  • Study diseases and insects resistance.
  • For Virus indexing in research programs.
  • Tolerance to different types of soil.
  • Limitations of Grafting
 Like in other propagation methods grafting has limitations. 
  • Methods of grafting may required additional facilities during aftercare to provide a controlled environment.
  • Specialized personnel with consequently higher remuneration.
  • Additional cost that involved growing or purchasing rootstocks.
  • Incompatibility between rootstock and scion.
  • Undesirable changes in the normal growth habit.

 

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