The demand for conifer trees (e.g., pines and firs) to make wood products continues to increase. One proposed solution to this problem is to identify individual trees that possess desirable characteristics, such as a rapid rate of growth, and produce numerous, genetically identical clones of the superior trees by somatic cloning. Somatic cloning is the process of producing plant embryos, in vitro, from plant cells that are not zygotes. These clones can be cultivated to yield stands, or whole forests, of conifer trees that possess the desirable characteristic(s).
One method for somatically cloning trees utilizes in vitro treatment of isolated, living, conifer tissue under conditions that promote formation of conifer somatic embryos, and then whole plants, from the treated tissue. The isolated conifer tissue may be cultured in the presence of one or more auxins, and/or cytokinins, to promote formation and multiplication of embryogenic tissue that is then cultured under conditions that promote formation of cotyledonary embryos that are morphologically similar to zygotic embryos produced in vivo. The embryos may then be germinated to yield conifer trees. An example of conifer embryogenic tissue are embryonal suspensor masses (ESMs) that can be formed, by tissue culture in vitro, from conifer embryos dissected from conifer seeds. By way of example, FIG. 1 shows pine embryonal suspensor masses in liquid culture. FIG. 2 shows a pine, cotyledonary, somatic embryo formed from ESM (cotyledons are visible at the top of the embryo).
A continuing problem, however, is stimulating efficient formation of conifer, cotyledonar, somatic embryos that are capable of germinating with high frequency to yield conifer plants. Preferably, the conifer cotyledonary somatic embryos, formed in vitro, are morphologically, anatomically and biochemically similar, or identical, to zygotic conifer embryos formed, in vivo, in conifer seeds of the same species. In particular, there is a need for methods for producing, in vitro, greater numbers of zygotic-like cotyledonary somatic embryos than are produced by prior art methods. Preferably, the germination frequency and quality of the conifer, cotyledonary, somatic embryos produced by the novel methods should be higher than the germination frequency and quality of conifer cotyledonary somatic embryos produced by prior art methods.