Grafting in Conifers: A review

Grafting is one of the vegetative propagation methods most commonly used worldwide to preserve genotypes and increase germplasm production. The method involves the insertion of a scion from one individual plant into a rootstock from another individual to form a single plant. It has been widely used in fruit trees and hardwoods, but much less so in conifers. Grafted trees are used to establish asexual seed orchards for producing forest germplasm and thus yield genetically improved seed on a large scale. Sprouting processes (callus formation) in the grafted plant are affected by several factors, the most important of which are the technique used, grafting season, phenological and physiological state of the scion and the rootstock, taxonomic affinity between the organs, age of buds and rootstocks, microclimatic conditions of the site where the grafts are maintained, and genetic, anatomical and histological differences between the grafted organs. On the other hand, graft incompatibility can be caused by extrinsic or intrinsic factors. Grafting is also used to rejuvenate mature trees (upper buds), and it is possible to shorten the process by applying growth promoting hormones. Good results have been achieved with conifers in grafting tests conducted in the United States and some parts of Europe and Asia; however, successful grafting and survival of conifer grafted rootstocks have not yet been achieved in Latin American countries.