Grafting is the most widespread technique to propagate fruit plants in an agamic way. It consists of joining two different portions to form a single individual. Of the two parts, which each take the name of bionte, one will provide the root apparatus (rootstock-subject), the other the epigeal part (object). Generally the graft is performed with two blondes, but it is also possible to have the graft in three different parts (grafting-grafting). Grafting is used in special cases, ie to overcome the difference between the parts that would not allow the creation of a vascular continuity. Instead, the re-grafting is used to renew a plant already in production with new varieties. The grafts can be classified in various ways and one of these concerns the vegetative stage of the two blondes on the basis of which: herbaceous grafts (subject and graft are not lignified), semi-woody grafts (lignified rootstock, herbaceous grafting) and wood grafts (rootstock and graft are both lignified). The graft, in addition to guaranteeing the continuity of genetic characters like all other agamic propagation systems, offers many other advantages that justify its widespread use. The most important are: the possibility to choose between various rootstocks; adapt the plant to the type of soil and climate; plant cutting rule to give strength to the foliage; disease prevention; and finally, it facilitates the renewal of the varieties of the orchards when these exhaust their vegetative period avoiding the suppression and the consequent new replanting. Among the various types of grafts we focus on the detailed description of the graft called "crown".
CORRUGATION: CROWN: USE
The crown graft is used both to re-implant adult plants and to plant young nurseries. The number of scions (sharp branches) to be used therefore, is closely related to the diameter of the trunk or branches and to the number of branches that you will want to develop. Compared to the triangle graft, the crown one has fewer problems of subject-to-grip adherence. But being performed mainly in a more advanced period (March-April-May), as it is essential that the rootstock is in "suck", the scions will have a more limited development at the end of the vegetation. However, the crown graft is preferable for stone fruit, because it limits the emission of rubber resulting from deep incisions; and it is preferred to the triangle grafts that perhaps in the previous months did not have a positive outcome. This technique is very widespread in order to revitalize and expand the productivity of fruit plants such as plum, apricot, almond and cherry.
PLUG IN CORONA: THE TECHNIQUE
Before starting this technique, the subject must be cut a little above the chosen graft point. This operation, carried out in time during the vegetative rest, must be repeated before grafting with the removal of that portion left with the first cut. Along the circumference, where the scions will be inserted, slightly inclined cuts will be made, to prepare the support surfaces for the scions. The latter obtained from branches of about a year, well lignified and not yet in vegetation (it is preferable to collect them in winter and keep them in the fridge), they are prepared with a first incision at 3 centimeters from the base, perpendicular to the axis and slightly inclined from the outside to the inside so that it affects about two thirds of the trunk diameter. Throughout this thickness the wood will be removed by cutting it lengthwise so that the base of the scion results in a "clarinet beak". From the part that is diametrically opposite to this, just shaped, the bark will be removed for 1 or 1.5 centimeters without affecting the wood.
COUPLING IN CORONA: CONCLUSIVE PHASE
The road leading to the completion of the crown graft involves other small but no less important steps. We will therefore try to unglue the rootstock, where the slightly inclined planes, the bark from the wood, have already been prepared. In this place the scion will then be inserted, leaning it against the subject on the first horizontal incision. If the operation of "detachment" of the bark was a bit difficult, a long vertical incision can be made as the shaped part of the scion. When the latter is inserted the edges of the subject's bark are placed against it, the point of graft is tied and as with all types of graft the free surfaces covered with the putty. The binding of the graft point can be performed even before the insertion of the scion. This ensures that the bark detached from the subject does not tear during insertion of the scions. For drupaceous plants the technique of crown coupling it is practiced for the apricot tree in February-March; for the plums in the months of May-June; for the cherry, the best period is between March and April; finally for the almond having a rootstock with good productive characteristics the most suitable period goes from April to May even if, having an early productivity makes it possible that already in the first decade of March it is possible to carry out the grafting operation. Finally, a note should be given to soils suitable for crown grafting in stone fruit, which must be of medium, fresh dough, immune to water stagnation, therefore with the total absence of limestone to which the almond is susceptible; however the percentage of limestone in the latter must never exceed the 5% threshold.