W.H. CRAMW.H. CRAM is superintendent of the Tree Nursery Division, Canada Department of Regional Economic Expansion.
FOR THE PURPOSE of this paper " other high-yielding characters " are such as resistance to climatic and urban stresses, production of nectar from flowers, tannin from bark, sugar from sap, resin from gum, and amenity values for shelter and landscape. These characters, while not necessarily related to timber yields, provide economic advantages to society if developed through the application of tree breeding practices.
For the most part the characters to be considered are controlled by multiple genes and are not simply inherited, so reproduction of the desired phenotypes is difficult. Too frequently, selected seed trees are of a heterogenous nature for many factors, including the characteristic desired. Mass reproduction of such selections by vegetative propagation is the only quick and easy way of exploiting trees having desired combinations of characters. However, asexual reproduction often presents insurmountable problems, so that seed provides the only economic and practical means of reproduction. For further discussions of mass reproduction see Fielding (1969) and Cram (1969).
The following presentation is not an account of all tree breeding activities for such factors. It is merely a review of recent advances as reported by others at this consultation. In addition, mention is made of maple syrup from sap and resin from gum.
Certain extreme environmental and climatic conditions are detrimental to culture of trees, so improvements by breeding should provide trees adapted to extreme conditions.
COLD RESISTANCE
Selection and propagation of varieties which flush late in the spring and cease growth early in the autumn present possibilities for preventing damage by spring and autumn frosts (Holzer, 1969; Lacaze, 1969. For the most part, cold resistance or frost hardiness is not a critical factor for species indigenous to the temperate zone and presents no problem for Picea abies (L.) Karst where it attains its optimum development. However, in mountainous countries and particularly at the limits of distribution of a species, it is important.
On the other hand, resistance to late spring frosts that occur during flushing time necessitates selection for late flushing plants. For example, Kriebel (1957) found that southern sources of Acer saccharum resisted late spring frosts more than northern sources with earlier bud break. Similarly, winter and autumn frost damage is overcome by selection of provenances and progenies which stop growth soon enough to avoid injury. Cold resistance obviously depends on the single and combined expression of many traits. Ways need to be developed to study these traits under controlled conditions.
DROUGHT RESISTANCE
Resistance to drought has been described (Bolotin, 1969) as a polygenic trait involving roots, foliage, transpiration, osmosis and ability to withstand water losses. Progeny tests are recommended to detect drought resistant individuals and to identify hereditary characters associated with drought resistance. Selection of ecotypes having natural resistance in dry habitats is another promising way to develop drought-resistant varieties. A major problem in studying drought resistance is the lack of standardized procedures for testing.
URBAN STRESSES
Conditions under which urban trees must live include stress factors of soil compaction, air pollution and salty soil (Santamour, 1969). Species and individuals tolerant to such environmental stresses can be identified. Superior selections may be propagated as clones by cuttings or grafting. Combinations of clones with good tolerance to air pollution grafted onto clonal rootstocks with tolerance to soil compaction and salt could produce trees especially adapted to urban environments.
This programme requires stringent selection criteria and unique designs for progeny tests. Efforts to reduce the severity environmental stress factors for urban trees should also be considered if trees are to survive and prosper ill the cities of tomorrow.
SHELTERBELTS
Selection of seed sources by evaluation of provenances provides a breeding technique for the establishment of shelterbelt trees adapted to specific climates, altitudes, soils or geographic areas of the world. Preliminary survival observations of young provenance plantings for Pinus radiata (Eccher, 1969) demonstrated the superiority of an Italian seed source for shelterbelts in Italy. Survival of mature Scots pine plantings (Cram and Brack, 1953) demonstrated the superiority of a Russian provenance for the adverse climatic conditions of the Canadian prairies. Schmidt-Vogt (1969) found major differences among provenances of Alnus glutinosa in extent of root development. Obviously root systems influence windfirmness and resistance to desiccation and deserve more attention in tests of provenances and progenies. (dram (1969b) summarized results of a breeding programme designed to improve the vigour of Caragana arborescens for shelterbelt plantings in the Canadian prairies. Hybrid progenies from cross combinations of vigorous and self-incompatible selections have demonstrated 27 percent greater height than open-pollinated progenies in nine years.
NECTAR FOR BEES
Selections of Robinia pseudoacacia. I,. with higher sugar content of the nectar and with later and longer periods of flowering (Keresztesi, 1969) have significantly increased honey-bee pastures and improved aesthetic aspects by afforestation of regions and shelterbelts. Of the total commercial honey production in the forested area of Hungary, 80 percent originates from R. pseudoacacia stands, occupying 21.5 percent of the forest area.
The annual yield of honey per hectare of forest amounts to more than U.S.$26, almost exactly half the value of wood produced per hectare. Thus, the importance of breeding to enhance honey production is obvious. Some 32 selections have been propagated and evaluated.
TANNIN YIELDS
Phenotypic selection for tannin content and possibly bark thickness (Nixon, 1969) could be effective for the economic improvement of Acacia mearnsii. Relationships among parent tree selections and half-sib progenies were highly significant for vigour as expressed by bark thickness and diameter.
Tannin content correlated with both of these component characters, but individuals or families with a high tannin content are not necessarily the most vigorous. Phenotypic selection for tannin and to some extent for bark thickness should be effective in increasing production of tannin.
LANDSCAPE VALUES
Embellishing landscapes with forests and trees adds to their natural beauty. Breeders can contribute by producing trees with desirable traits of spring blossoming, leaf colouration, particularly in autumn, unique shapes of stems and branches, fruit production for man or wildlife, bark colouration and texture. Keresztesi (1969) reports on selection of Pinus sylvestris L. and Populus for aesthetic values Intensity of the blue-needle colouration factor for Picea pungens appears (Cram, 1969a) to be genetically controlled because hybrid progenies of some combinations between parental selections proved consistently superior for this character. Two selected parents producing these superior 'blue" progenies are being propagated by grafting for establishment of a natural crossing block, to produce hybrid seed by natural cross pollination of the self-incompatible parents.
STEM EXUDATIONS
Breeding improved strains of Pinus elliottii var. elliottii for increased oleoresin yield is being carried out by the U.S. Forest Service. Squillace and Fisher (1966) provided evidence on the inheritance of composition of turpentine. Development of a juvenile screening method for potential oleoresin yields (Squillace and Gansel, 1968) has permitted screening of progenies after two years in the nursery. Selections from F1 progenies have been released for seed orchard establishment and commercial-scale seed production is under way.
The sap of Acer saccharum Marsh. is used for the production of syrup and sugar in the northeastern United States and adjacent Canada. The U.S. Forest Service has initiated a breeding programme in Vermont to develop maple with greater sap yields of higher sugar content. Summaries of the reproduction and genetics of sugar maple have been published by Kriebel and Gabriel (1969). Plus trees have been selected and collected into a breeding orchard for future research.
Other papers presented at the Washington consultation provided information on the selection and inheritance of many traits other than those influencing wood production. All these have economic ramifications. In order to utilize the practical advantages of these special traits, desirable phenotypes should be selected and bred by the appropriate system to produce superior progenies.
BOLOTIN, M. 1969. Selection for drought resistance in woody species. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/3.
CRAM, W. H. 1969a . Breeding and Genetic of Caragana. For. Chron., 45(6): 1-2.
CRAM, W. H. 1969b . Use of self-incompatibility factors for hybrid seed production. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-11/17.
CRAM, W. H. &; BRACK, C. G. E. 1953. Performance of Scotch pine races under prairie conditions. For Chron., 29: 334-342.
DAVIS, T. A. 1969. Variation in the staminal bundles of the wild silk-cotton tree (Bombax ceiba Linn.) Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/11.
ECCHER, A. 1969. Preliminary observations on trials for some Pinus radiata D. Don provenances in Italy. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/8.
FIELDING, J. M. 1970. Mass production of improved material. Unasylva, 24(2-3).
HOLZER, K. 1969. Late frost injury in an alpine Norway spruce (Picea abies [L.] Karst) provenance test. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/2.
KERESZTESI, B. 1969. Selection of forest trees and shrubs for improvement of the bee pastures and in favour of the landscape architecture. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/5.
KRIEBEL, H. B. 1967. Patterns of genetic variation in sugar maple. Ohio Expt Sta. Res. Bull. 791. 65 p.
KRIEBEL, H. B. & GABRIEL, W. J. 1969. Genetics of sugar maple. U.S.D.A. Res. Pap. WO-7. 17 p.
LACAZE, J. F. 1969. Héritabilité du caractère débourrement végétatif dans une population d'épicéa du 2e plateau du Jura. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/13.
NIXON, K. M. 1969. Selection for components of bark and tannin yield in black wattle (Acacia mearnsii DeWild). Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/6.
SANTAMOUR, F. S. 1969. Breeding trees for tolerance to stress factors of the urban environment. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/4.
SCHMIDT-VOGT, H. 1969. Growth and root development in Alnus glutinosa of different provenance. Second World Consult. Forest Tree Breeding. FAO-FO-FTB-69-6/12.
SQUILLACE, A. E. & FISHER G. S. 1966. Evidences of the inheritance of turpentine composition in slash pine. U.S.F.S. Res. Pap. NC-6, p. 53-59.
SQUILLACE, A. E. & GANSEL, C. R. 1968. Assessing the potential oleoresin yields of slash pine progenies at juvenile ages. U.S.F.S. Res. Note SE-95. 4 p.
