Genetic manipulation of wood of the southern pines including chemical characteristics

Summary

A review of possible changes in wood morphology through genetic manipulation of the southern pines showed that:

• 1. Significant changes can be obtained by modifying tree form, growth rate and disease resistance.

• (a) Compression wood can be reduced by developing straighter trees. The inheritance of straightness is so strong that one generation of selection has resulted in enough improvement to enable deemphasis of this characteristic in second-generation breeding.

• (b) Branch size affects the final product by knot volume and the associated compression wood, included bark and resin; it is moderately genetically controlled.

• (c) Use of disease-resistant trees not only results in greater wood volume but in higher quality wood. Logs infected with fusiform rust give lower pulp yields and lower mullen and tensile strength in the paper.

• (d) Growth rate has a limited effect on wood qualities in mature loblolly pine. It is possible to have fast growth combined with either high or low specific gravity wood, since these characteristics are not closely related genetically.

• 2. Inheritance of wood qualities per se is strong enough to obtain meaningful changes in both yield and quality of pulp and paper.

• (a) Wood specific gravity, which is really a complex of several characteristics, has responded well to selection. Specific gravity differences affect yield, quality and cost from harvesting to the end product.

• (b) Cell wall thickness appears to be the most important morphological characteristic that affects pulp and paper qualities; it is moderately genetically controlled directly and also controlled through specific gravity.

• (c) Pulp yield per unit volume increases when specific gravity is increased; also, 1 to 7 percent greater yields are found per unit weight dry wood.

• (d) Parent trees with juvenile wood of high or low specific gravity produce progeny with juvenile wood similar to the parents. Pulping tests showed high gravity juvenile wood had characteristics similar to mill run chips.

• (e) Moisture content inheritance closely parallels that of specific gravity.

• (f) All important wood morphological characteristics tested are under enough genetic control to obtain useful gains.

A review of the inheritance of chemical characteristics revealed the existence of few definitive studies. Cellulose yield is inherited in such a manner that selection will not be effective, whereas, oppositely, resin content is inherited in a manner allowing gains to be made through selection. Because of the relationship between chemical characteristics and wood morphological characteristics such as specific gravity, breeding for one will generally affect the other.

A previously unreported study of six trees from six control-pollinated families, all of which had the same mother but different fathers, showed that the sugar contents of the six families were essentially constant; glucose varied from 65 to 70 percent but this difference was not statistically meaningful. Polysaccharide differences were not closely related to specific gravity. Because of the close relationship between morphological and chemical characteristics it is the author's opinion that breeding for chemical differences should be limited to those instances in which it is specially useful for yield improvement.

It is possible to manipulate wood in a desired direction by breeding for characteristics that affect wood or by breeding for the wood characteristics directly. Enough is now known about the effect of differing wood properties on the final product so that the worth of changes obtained can be assessed in terms of economic or utilization values.