Christmas Tree Genetics Program
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Tree Improvement Program
Tree improvement is the application of genetic principles to increase the value of tree crops. Recently, tree improvement programs for species important to North Carolina's Christmas tree industry have been initiated. Each of these program is uniquely tailored to the individual species according to their biologic constraints and importance to the state's industry.
- Fraser Fir
- Virginia Pine
- Eastern White Pine
- Eastern Redcedar
- Leyland Cypress
The Tree Improvement Process
Limbs & Needles. 1996. Vol. 23(4):10,12,14.
Introduction
Tree improvement is the application of genetic principles to increase the value of tree crops. Worldwide, tree improvement techniques are being employed on virtually all commercially important forest tree species to the enhance economic returns from wood and paper products. To date, most tree improvement efforts directed at Christmas tree production have been either superficial or non-sustained. Recently, however, the North Carolina legislature has responded to growers’ needs by providing funding for a Christmas tree genetics program. The development of focused tree improvement programs for Christmas tree species important to the state including Fraser fir, Virginia pine, eastern white pine and eastern redcedar are currently underway at North Carolina State University. These new programs will integrate and build upon past Christmas tree genetics efforts by NCSU, the North Carolina Division of Forest Resources and other organizations. This article presents an introduction to the overall tree improvement process.
Improvement Overview
Tree improvement relies on understanding and using variation that naturally occurs in tree populations. Tree improvement increases the value of a tree species by 1) selecting the most desirable trees from natural stands or plantations, 2) breeding or mating these select trees and 3) testing the resulting progeny. The trees involved is this process are referred to as the breeding population. This three-step process is then continuously repeated to further improve the average value of the breeding population. Each iteration of this improvement process is referred to as a generation. See Figure 1 & Figure 2 for graphical representations of the tree improvement process.
The production population is another group of trees established to meet commercial planting demands. Usually the production population is a seed orchard or group of trees at a single location managed specifically for seed production. For species which can be readily propagated using rooted cuttings, a hedge orchard managed to produce cutting material may serve as the production population. Seed and hedge orchards generated from a tree improvement program are established from grafts, rooted cuttings or seed of the very best trees in the breeding population.
Selection
Tremendous variation exists in natural stands for many important Christmas tree characteristics such as growth rate, color, branching habit and disease resistance. Growers often encounter this variation in their Christmas tree plantations. Observed characteristics such as growth rate are referred to as the phenotype of a tree. A tree’s phenotype is determined by both its genetic constitution, or genotype and the effect of the environment as described by the following equation:
P = G + E
where,
P = phenotype
G = genotype
E = environment.
When selecting trees, what you see is not necessarily what you get. Genetically inferior trees may sometimes appear phenotypically desirable because they grew in an unusually favorable micro-environment. Conversely, genetically superior trees may appear phenotypically undesirable due to poor environmental conditions. Characteristics vary in the degree of genetic versus environmental influence. For example, genetic control of branching habit is stronger than for height growth so that the selection process is generally more effective for branching traits.
Initial selection of trees from natural stands or unimproved plantations are necessarily based solely on phenotype. Since the variation due to environmental effects is less in plantations than natural stands, selection is more effective in plantations. In order to ensure that the selection process is as effective as possible in unimproved stands, candidate trees are graded according to predetermined criteria. Both the candidate tree and neighboring check trees are measured and compared in order to account for local environmental effects. Once a tree improvement program is underway, genetic information (performance of relatives) is used to increase the effectiveness of the selection process.
Breeding
The next step in the tree improvement process is mating or breeding among the select trees. For this purpose, branch tips or scion of each selection are grafted onto seedling rootstock to establish a breeding orchard. Control-pollinations are then performed among the selections. Control-pollination starts with covering receptive female cones with bags during early spring to prevent natural pollination. Pollen collected from other select trees or mixed from a group of select trees is then injected into the pollination bag. After pollination has occurred, the bags are removed and the cones allowed to ripen. Each cone-producing branch is labeled to ensure correct identification at cone harvest. Control-pollination is performed according to certain mating designs among the select trees in order to maximize the overall genetic information derived from the resulting progeny.
Testing
Seed produced from tree improvement breeding efforts are used to establish progeny tests. The purpose of these tests are to 1) provide genetic information about the select parent trees and 2) provide an improved population of trees from which the next generation of select trees is made. Tree families established in progeny tests are randomized and replicated in a designed manner to meet statistical and genetic criteria. Families are planted in several sites and in more than one year to sample an adequate number of environmental conditions. Christmas tree progeny tests are intensively managed similarly to a typical Christmas tree plantation. Growth and quality measurements are made periodically in these tests until harvest. These data are entered into a data base and analyzed. The results are used to assess the genetic worth of the original selections, to make selections for the next generation and to make recommendations for establishing and upgrading seed and hedge orchards.
Final Remarks
Tree improvement is the successive application of selection, breeding and testing to continuously improve the value of a population of trees. The best trees of the population are used to propagate planting stock for commercial plantations.
While the Christmas tree industry stands to reap tremendous benefits from tree improvement, it should not be viewed as a panacea. Tree improvement is one of many tools needed to continue to improve the productivity and quality of Christmas trees crops. Growers must continue to use the best available technology to manage their plantations. In fact, the greatest benefits from tree improvement will be achieved on the best sites receiving the best management.
Due to the nature of trees, the tree improvement process requires both a large-scale effort and a relatively long time-frame to achieve its results. Researchers, extension personnel, government and commercial propagators, and growers must all cooperate to ensure that these results are realized as rapidly as possible. While hard work and patience will be required, the Christmas tree industry will be rewarded with new standards of productivity, quality and profitability.
Figure 1. Diagram of the tree improvement process. Selection, breeding and testing are repeatedly carried out in the breeding population (left column) while the production population (center column) produces seed for commercial use (right column).
Figure 2. The variation of most important Christmas tree traits can be described with a bell-shaped or normal distribution. This distribution is symmetric around the average value with fewer trees occurring as the value increases and decreases from the average. In a tree improvement program, the best trees in the upper tail of the distribution (yellow areas) are selected. These select trees are then bred and their progeny are established in test plantations. Successive generations of selection, breeding and testing are carried out to further increase the average value of the breeding population.
Reprinted from Limbs & Needles with permission.
