Understock

In Arboriculture and Vine growing, a understock is a subject on which one establishes a graft.

The species (or varieties) used to make understocks are not very demanding species which multiply easily by Semis or generally by vegetative Multiplication (propagation by cutting, layering).

They are generally selected for their qualities (strength, morphology, adaptation to the type of ground and the climate, resistance to the diseases…) that they will transmit to the graft.

For example, for the Cherry tree S, one grafts on Merisier for the high ones - stems and on Cerisier of St Lucia for the Espalier S.

More recently, the nurserymen started to choose their understocks not to adapt the orchard to the nature of the ground but more to implement farming strategies where the heights of tree and the densities of plantation are learnedly calculated. For the orchards of apple tree for example, one observes two tendencies: 800 to 1000 feet per hectare with MM106 and 1500 to 3000 feet per hectare with of M9.

Understock for citrus fruits

The majority of the Agrume S supports the cold climates very well (see negative for some -20°C) one thus uses a rustic species, the Poncirus, like understock, which allows certain citrus fruits grafted on Poncirus to push there or they could not it on their own roots.

Understock for apple trees

The understocks most used for the culture of the apple trees were developed by the East Malling Research Station in England. They are unknown under the name of Malling series and Malling-Merton series.

Understock for pear trees

To graft pear trees, one can use the following understocks:

  • the Sowing of pear trees (Pyrus communis) which give understocks of strong strength and often sensitive to the bacterial Feu. The franc of pear tree Kirchensaller and the American series of pear trees OHF (crossings of the Thirties of Old Home and Farmingdale, resistant to bacterial fire but with difficulty bouturables) are promising but still not very widespread…

  • sowings or cuttings of pear trees of China (Pyrus calleryana) used as understocks for the common pear trees and the Nashi S (Pyrus pyrifolia). Some cultivars are resistant to the diseases (Chancre, bacterial fire, etc) but their use is especially developed in China and in the United States.

  • Cormier (Sorbus domestica), Sorb of the bird-catchers and Aubépine (Crataegus sp.) is of anecdotic use, reserved to the private individuals and often of low longevity.

  • the Cognassier S, which are alternatives of average strength very much used in France (even if incompatibilities with the varieties Williams and Guyot, very cultivated commercially, pose problem). However, if the quince tree tolerates grounds Argile ux; in grounds Calcareous, the quince tree presents a Chlorose due to the blocking of the Fer. That brought the selectors has to try new selections of individuals resistant to chlorosis, in particular starting from cultivar BA29.

In parallel, crossings of pear trees and selections of quince trees are always tested… And certain studies seem to show that certain sowings of pear tree “Williams” present a reduced strength and weak symptoms of chlorosis

References

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