Treesearch

Homozygous trees will never be the desired ultimate step in a forest tree improvement program. However, they will serve many purposes in forest genetics research: (1) in the detection of genetic markers; (2) in the isolation of traits under simple genetic control for the study of growth and differentiation phenomena; (3) as a tool as well as reference material in the study of breeding mechanisms in natural populations; (4) as reference material in a study of the efficiency of different selection schemes; and (5) in the study of sex control mechanisms in dioecious species. Furthermore,...

Within-species variation in turpentine composition has promise of great utility in pine genetics. Most of the early work on turpentine composition dealt with species differences, and the utility of such variation in the taxonomy of pines is well known (Mirov 1961). With the development of gas chromatographic techniques, intensive study of individual tree differences has become possible (Bannister et al. 1959; Williams and Bannister 1962); and this type of variation has been shown to occur in several pine species (Bannister et al. 1962; Blight and McDonald 1964; Smith, 1964a).

The initial size of conifer seedlings is closely related to seed size (Hadders 1963), and seed size is a maternal characteristic that is highly subject to environmental modification (Mergen et al. 1964; Righter 1945). The effect of seed weight must be accounted for in critical studies of seedlings which attempt to attribute differences in growth to specific genetic or environmental causes (Duffield 1960; Mitchell 1934, 1939).

Many seed orchard programs include a stage at which clones or seedlings are culled on the basis of progeny tests. Though breeding systems which involve progeny testing differ in efficiency, they all provide information on an individual's breeding value through its own performance and that of parental or seedling relatives. A combined index on any one trait, using information from a set of relatives, is desirable. However, tree breeders appear to be planning only limited use of indices on data from relatives. In so doing, they may be foregoing a considerable advantage, for the increased...

Readily identifiable phenotypes, such as cotyledonary chlorophyll deficiencies, whose genetic basis can be established, would be highly useful in forest genetics research as genetic markers. In the genus Pinus mutants with severe deficiencies, such as albinos, will die shortly after seed germination while those with less severe deficiencies will not. In either case, however, the symptoms appear in early stages of growth and hence these types of mutants are especially useful as gene markers.

One of the principles of experimental design is that replicates be relatively homogeneous. Thus, in forest research a replicate is often assigned to a single crew for planting in a single day on a uniform site. When treatments are numerous, a large area is required per replication, and homogeneity of site is difficult to achieve. In this situation, crop scientists (LeClerg et al. 1962) frequently divide the replicate into sub-blocks. The most used of the incomplete block designs are the lattices. Another type of incomplete block designs, the compact family block (Hutchinson and Panse 1937;...

In the genus Pinus, much of the information about species crossability that has accumulated during the past three decades has reinforced ideas about the relationships of pines based on other kinds of evidence. There are some conspicuous exceptions to this generalization, however, and the most thoroughly investigated of these exceptions is Jeffrey pine (Pinus jeffreyi Grev. & Balf. ), an economically important forest tree of montane California and adjacent parts of Oregon, Nevada, and Baja California. Biochemically, this puzzling species is much like the Sabinianae Loud. (Macrocarpae Shaw),...

Picea schrenkiana Fisch and Meyer is a relatively unknown central Asiatic species confined to the Ala Tau and Thian Shan mountains of Turkestan. Morphologically the species is most closely related to P. spinulosa (Griff.) Henry and, to a lesser degree, to P. obovata Ledeb. (Wright 1955).

Maximum early gains in the genetic improvement of eastern cottonwood (Populus deltoides Bartr.) in the lower Mississippi Valley are most likely to be achieved through identification and commercial vegetative propagation of superior genotypes. A relatively simple improvement program having this goal might include evaluation of progeny from phenotypically superior mother-trees followed by clonal tests of outstanding juvenile phenotypes selected from progeny. Such an approach is being used in the first phase of the cottonwood improvement program at the Southern Forest Experiment Station. This...

The reproductive systems of forest trees that have evolved in wild habitats are usually characterized by delayed flowering age, cyclic seed years, and possibly an optimum, rather than a maximum, number of seeds per tree. Presumably these characteristics are favored by natural selection, though not necessarily in all species or in all situations.