Mature seeds are used to propagate rootstocks. Seedlings may be grown from fresh seeds collected in the fall and stratified at approximately 45°F for 60 to 90 days. After stratification the seeds can be germinated in boxes at 70°F, although germination from seed has a relatively low success rate (25-35%). Seedlings are lined out in the spring when the soil temperatures are 55°F or higher. Plants develop a better lateral root system when they are transplanted at 6 to 8 inches tall. Seedlings can be grafted at the end of one season’s growth, when the rootstock and scion are dormant (LaRue et al., 1982).
Grafting should be conducted during the dormant period, before vegetative growth begins, on rootstocks at least 1/3 inch diameter. The scion wood should be 1/4 to1/3 inch in diameter and about 3 to 5 inches long with 2 to 4 buds. Scion cuttings should be collected from healthy, well lignified plants during winter dormancy and kept in cold storage until the time of grafting. A whip and tongue graft is used when the diameter of the scion is thin, while a wedge graft is appropriate for scions with thicker diameters (Bellini, 2002).
To propagate rootstocks with cuttings use softwood cuttings, root with bottom heat under mist, and treat with indole-3-butyric acid (IBA) (Hartman et al., 2010). Rootstocks from cuttings can also be obtained by removing large sized roots from young plants. These cuttings are put in a greenhouse under mist and moved to a nursery in the spring. Self-rooted cuttings can support a graft within one year (Bellini, 2002).
Micropropagation is a method used to produce a large number of identical plants from a small amount of plant tissue. This method is advantageous when there is a limited source of plant tissue; however, it is labor intensive and expensive, requiring sterile laboratory facilities. The performance of micropropagated trees varies by cultivar. For example, micropropagated trees of cultivars ‘Jiro’ and ‘Hiratanashi’ grow easily and more quickly than grafted trees and showed less shock at transplant compared to grafted trees (Tetsumura et al., 1999).