Cultivar Selection And Stem Cutting Propagation Of Magnolia Grandiflora

Magnolia grandiflora L. (Southern Magnolia) is a beautiful evergreen tree, native to the southeastern US. It is a very popular and important landscape plant for shade trees and everyday gardens. The plant is always attractive by its beautiful habits, leathery lustrous dark green foliage, and magnificent creamy white and fragrant flowers. At abroad, more than 80 cultivars of Southern Magnolia have been selected and vegetatively propagated for the commercial nurseries. After the plant was introduced to China more than 100 years ago, it was widely planted in Central and Southern China. However, only one cultivar was published and it was not found in commercial industries. Since Southern Magnolia is mainly propagated by seeds, it is understandable that no cultivar is available in the market and the potential for selecting new cultivars from seedling populations is great. With the increasing of market demand on new cultivars and their clonal propagation techniques, this project was conducted on selecting and clonally propagating of Magnolia grandiflora. The selection and propagation were limited to Changsha and adjacent areas and the conclusions were:(1) Two new cultivars, Magnolia grandiflora'Bixia'and Magnolia grandiflora'Dalun' were selected based on their habits and morphological uniquenes.'Bixia'is selected for its light green, glabrous leaves and rounded habit;'Dalun'was selected by its narrow pyramid habit and dense foliage. Anatomy of their leaf epidermis further verified their differences by their structures of upper epidermis cells, stomata density, and surface coverings.(2) Magnolia grandiflora could be clonally propagated by stem cuttings. The better time to take hardwood cuttings was November, when the stem active growth was slow down and enough carbohydrates were cumulated for overwintering. Softwood cuttings collected in June were also feasible for rooting of Southern Magnolia. March and August of the year should be avoided for collecting stem cuttings. Stem cuttings of Southern Magnolia should be treated with rooting hormones. The highest rooting percentage,70.8%, was obtained under the treatment of K-IBA at 20 g/L. During November, K-IBA concentrations from 10 to 20 g/L could be applied for rooting of stem cuttings. K-NAA concentrations from 5 to 20 g/L had the similar effect of K-IBA (> 50%). Both IBA and NAA could increase rooting rates of Southern Magnolia. However, potassium salts of rooting hormones worked better than other carriers because they could be directly dissolved in the water (not alcohol). The quality of roots followed the same trends as rooting percentages.(3) The anatomy of stem transverse sections indicated that root formation of Southern Magnolia cuttings originated from both cambium tissues and callus. For future studies, we should induce adventitious root formation of Magnolia grandiflora from both positions and improve its root percentage and quality. The findings could be also applied for studies of other species in Magnoliaceae.