Abstract
The establishment of clonal seed orchards is a viable option for the continuous production of improved seed of desired genotypes. Grafting is the main technique used to establish clonal seed orchards. The objective of this study was to examine how the geographic location and the age class of the donor trees of buds, the phenological status of the buds, and the anatomical characteristics of the scions and the rootstocks affect the survival and growth of Pinus engelmannii Carr. grafts. Scions were collected from two trees in each of three age classes (young, middle-aged, and old). Grafting was performed with buds in two physiological states (end of dormancy and beginning of sprouting). Cross-sections of the grafted organs were obtained for anatomical analysis. A Cox proportional hazards model was used to determine the effects of the variables that were considered. The age class of the scion donor trees, the total area of the cut surface of the scion, and the density of resin channels in the scions significantly affected (p < 0.05) survival of the grafts. By contrast, the physiological state of the buds and the other anatomical characteristics of the grafted organs did not significantly affect graft survival. In P. engelmannii, grafting was most effective when scions from middle-aged trees were used. Graft survival was enhanced by a small total area of the cut surface of the scion and low density of resin channels in the scions. The area of the cambium of the scions directly influenced growth of the grafts.
Highlights
Grafting is a vegetative propagation technique that consists of joining parts of two different plants, which fuse together to form a callus, growing as a single plant [1,2,3].Vegetative propagation by grafting allows the preserving of genetic resources of high commercial, ecological, and cultural value [2].The provenance of the scion or barb has a greater effect on survival than the characteristics of the recipient rootstock when grafting Pinus taeda L. [4], and the quality of the rootstock that is used has significant effects on the survival and growth of the grafts [5]
Notwithstanding, since the grafting was undertaken at the end of the winter season, and the age of the rootstock was not variable under evaluation, we considered the possible growth that the rootstock underwent between the two grafting dates to be negligible
For the grafting of Araucaria angustifolia (Bertol.) Kuntze in Parana, Brazil, in April with average temperatures that fluctuated between −3 ◦ C and 18 ◦ C and with a high relative humidity, a survival of 60% was reported at 12 months after grafting [7]
Summary
Grafting is a vegetative propagation technique that consists of joining parts of two different plants (a scion with a rootstock), which fuse together to form a callus, growing as a single plant [1,2,3].Vegetative propagation by grafting allows the preserving of genetic resources of high commercial, ecological, and cultural value [2].The provenance of the scion or barb has a greater effect on survival than the characteristics of the recipient rootstock when grafting Pinus taeda L. [4], and the quality of the rootstock that is used has significant effects on the survival and growth of the grafts [5]. For the grafting of woody species, it is advisable to select scions and rootstocks of the highest possible quality [6]. Forests 2019, 10, 112 indicate that the best time to graft woody species is in the winter, i.e., between December and February in the northern hemisphere [7,8,9]. It has been noted in the literature that it is possible to graft conifers at any time of the year, if the temperature and humidity of the site where the grafts are maintained are controlled [10]. Several studies of conifers have demonstrated that grafting scions obtained from trees that are younger than 50 years of age increases the success of the grafting [1,7,11]
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