Chapter 20 Methods of Tree Breeding and Their Characteristics
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CHAPTER 20 METHODS OF TREE BREEDING AND THEIR CHARACTERISTICS In addition to choosing among several objectives breeders has led forest geneticists to devote con- when tree breeding projects are established, deci- siderable time to establishing arboreta and carrying sions have to be made in regard to specific traits to out species crossability studies. be improved and, what is equally important, the Introduction of forest tree species in the southern method or methods of breeding to be used. Im- United States has long interested landowners and provement in crop plants may be achieved in many foresters. Zon and Brisco (1911) described the suc- different ways, but all methods of breeding do not cess and failures of planted eucalypts in Florida apply equally well to southern pine problems, and dating from about 1878. Gemmer (1931) outlined the advantages of each method have to be balanced plans of the USDA Forest Service for testing intro- against the disadvantages. Also, the tree breeder duced pines in Florida. Locations at which exotic may have an opportunity to use several methods species are tested have been listed in a survey of simultaneously or to combine several methods. genetics and tree breeding research (Dormán 1966). Methods of tree breeding must be evaluated on the Many pine species have been test planted in the basis of genetic and tree breeding principles and, South and some survive, but overall performance most importantly, on the basis of the species and has generally been unsatisfactory. Results of plant- traits with which the work is to be done; cultural ings in Florida were summarized (Kraus 1963), as practices and forest products must also be con- were those in North Carolina (Barber 1953), Mis- sidered. A good method of breeding, in general, sissippi (Schmitt and Namkoong 1965), Louisiana may not be effective for a specific problem. (Grigsby 1969), Georgia (Jones 1966; Reines and Most tree breeding projects have limited time Greene 1956-57), and Texas (Zobel, Campbell, and funds; thus, efficiency or simplicity of various Cech, and Goddard 1956; Long 1973). breeding methods becomes very important, as All these pubhcations describe survival and other pointed out in the chapter on research needs. The information for imported pines in test plots in the chosen method must not only work, it must work southern United States. In no case did survival, better than any alternative method. Execution of a form, height growth, or resistance to insects and breeding plan requiring four generations of an an- diseases equal the general performance of native nual plant is far simpler than four generations of United States pines. Pines from the western forest trees. Thus, the tree breeder will concen- United States such as lodgepole, ponderosa, and trate on achieving the greatest gain in each genera- Monterey have been tried, as have pines from tion, rather than on only the results after a series of Mexico, British Honduras, Spain, Italy, China, generations. Korea, and Japan. Expectations for many years The individual tree breeding methods discussed were high, but results in this country have been here fit into the organization plan for the South virtually nil. described in chapter 16. Advantages and disadvan- tages of each method are discussed so that they can be used effectively at the proper time and place by the keyman in all this process, namely, the crea- Exotics for Large-Scale Planting in the South tive, applied tree breeder. Also, the more impor- The successful uses of exotics in forest planting in tant technical subjects that should be used to en- South America, South Africa, Australia, New Zea- hance various breeding methods are given. land, and some places in Europe are often cited as examples of the value of this work. It has been pointed out by Thulin (1957) that in Australia insuf- IMPORTATION OF NEW SPECIES ficient high-quaUty trees of Monterey pine occur per acre to justify establishment of seed production Introduction of new species of plants from dif- areas. This may come as a shock to many foresters ferent regions or different countries has been an who like to point to this work as a prime example of important part of breeding programs for many what can be obtained by tree introduction. It is species, and the same can be said of animal breed- quite true that Monterey pine grows very fast in ing. Nonlocal species have been used in two ways: Australia, but a selective breeding program is still to be placed directly into commercial production, or necessary to develop varieties of good quality. to be utilized in hybridization for the purpose of Form of southern pines planted in Australia was so combining one or more desirable traits with local bad that foresters started a tree selection program species. The success achieved by plant and animal in 1938 as part of a seed procurement project to 358 provide better planting stock. While introduction of such as poor form could be selected against in the Fi softwoods has been successful in Australia, there and subsequent generations so that a few undesira- have been no reports of the use of hardwoods to ble traits might not cause a species to be rejected replace eucalyptus. From the standpoint of forest for introduction, especially if it had a very impor- tree breeding in the southern United States, it is tant desirable trait such as resistance to a serious important to realize that, in general, pines exported pest. to other countries on a large scale have been either Complete testing of introduced species requires southern pines or pines from southern latitudes. that they be planted on a variety of sites in each Monterey pine is native in southern California, and climatic zone in the South. Many years must pass Mexican weeping pine is native to Mexico. Thus, before we can be certain what timber yield and the South already has or has test planted the wood quality will be and whether new species can species that are commonly imported by other coun- withstand exposure to all types of weather condi- tries. Introduction of the two nonsoutheastern tions as well as all types of disease and insect pests. pines, Monterey and Mexican weeping pine, have However, this process could be speeded up by using been unsuccessful in the South because of their inoculation techniques or growth chambers to simu- susceptibility to insect pests and cold damage. late climate conditions at various locations. Therefore, the introduction of species that are superior to the native southern pines does not, at this time, appear at all promising. Introduction of Advantages of Tree Introduction in the South hardwoods might be possible, but the South is well 1. In principle, it may be quicker and cheaper to supplied with these also. Arboreta planting is con- introduce a new species or variety if it exists than tinuing. Certain young eucalyptus trees grow fast to create one through a selective breeding program in south Florida. Something useful may show up in with local species. the future from this work, particularly as hybridi- 2. Even though not suitable for large-scale field zation material for disease and insect resist- planting, certain species may have genes or blocks ance or adaptability to poor sites. It is for this of genes that can be transferred to a native species reason that performance in arboreta should be care- that is weak in some character such as susceptibil- fully recorded so that records are obtained on form, ity to disease or insect attack. wood quality, and susceptibility or resistance to 3. Introduced species may provide much wider specific pests. This has not been done in the past; latitude in the choice of paternal stock in hybridiza- therefore, no records are available to show why tion than if only local species are used. For exam- certain species failed or if they had certain valuable ple, hybrid vigor may occur in crosses between traits. distantly related species, races, or varieties of the There are many ecological factors important in same species, provided, of course, that they will successful plant introduction work, and ignorance cross. or disregard of these factors has been the cause of 4. It is advantageous in hybridization work to most of the failures. Nearly always, trees do best have parental stock readily available. Although pol- when planted on sites and in climates very similar len of some trees such as the pines can be shipped to those of their origin. Seed should be obtained long distances, it is difficult to find competent from the better individuals and races of each people to correctly identify the species, collect the species. In the past, tree introduction has been pollen, and ship it to the tree breeder. most successful in Australia, New Zealand, South Africa, and parts of Europe where native species were few in number or species with wood of the Disadvantages of Tree Introduction in the desirable type—softwoods, for example—did not South exist. Quite the reverse is true of the southern forests; in fact, we are blessed by nature with the 1. It is costly and time consuming to test all the best of the pines and have Uttle chance of getting prospective tree species on a variety of sites in the better from somewhere else. South for an adequate period of time to insure reli- able performance data. Introduction for Breeding Stock 2. There is only a slight chance that species growing faster and having higher value wood than Use of non-native tree species to hybridize with local species will be found because there are a great local southern species may be of benefit in some number of southern tree species and many of them tree breeding problems.