20
Once the selection of provenances has been performed, progress can be made to
define seed-producing areas (SPA), which usually represent the most elementary
basic propagation material. SPA are natural stands or plantations, with good accessibility to the trees and their crowns, high productivity and low periodicity in seed
production, high specific purity in the case of possible inter-specific hybridization,
and with a mode of trees of good phenotype. The objective of the SPA is the provision of seeds from a known provenance. A thinning that eliminates undesirable
individuals (i.e., unhealthy, phenotypically diminished) will lead to the formation of
a seed stand (SS). This new basic propagation material already involves genetic
gain, even when it is based on light phenotypic selection.
The next step is the establishment of seed orchards (SOs), which are plantations
made with selected genetic material and with the specific purpose of producing
seeds for the plantation program. Clonal SOs are often the core product of the first
cycle of a high-intensity breeding program and require mastering the vegetative
propagation technique by grafting or rooting of cuttings. Progeny SOs allow dispensing with vegetative propagation, which is important to simplify the process and
occasionally crucial since in some species the percentage of success is very low (or
null) or depends on the genotype. In a low-intensity strategy, these progenies will be
the product of open pollination of the selected mothers. Thus, progeny orchards will
have greater genetic diversity than clonal orchards, which may be a particularly
sought-after effect if the goal is to increase adaptability rather than productivity.
However, open pollination involves the inclusion of many undesirable genes, leading to the need to test individuals in the orchard. In this way, the same group of trees
is a progeny trial and, simultaneously, the future seed orchard, which will only be
established when the genetic thinning prescribed by the trial evaluation is carried out.
However, monitoring and evaluating a progeny trial often exceed the possibilities
of a low-intensity breeding strategy. Gene source plantations (GSP) have been proposed as an alternative to progeny SO (Lindgren 2000). These are plantations established with seedlings from open pollinated selected trees, usually mass selected in
previous plantations or directly in the natural forest. They may be established in a
similar fashion to regular plantations and may serve concurrently several functions,
such as production of desirable commercial products, conservation of the genetic
diversity of the species, and as a local demonstration plot or as seed source for plantations, while retaining options to initiate a more regular improvement program. If
it will effectively function as a seed source, it should be thinned aiming to eliminate
undesirable individuals. The original material should include the seed of a high
number of mothers, since an intense thinning of their progeny could leave a limited
number of families in the GSP, thus favoring inbreeding.
Summarizing, recurrent selection cycles with recombination and infusions of
new material typical of high-intensity breeding are replaced, in low-intensity breeding, by linear chains leading to the development of a program with a predicted end
(Fig. 1.5). This does not mean that if the demand for seeds for productive or restoration purposes increases more than expected, the initial low-intensity program cannot be reformulated toward a new improvement cycle, moving in this case to a
classic high-intensity program.
M. J. Pastorino
Once the selection of provenances has been performed, progress can be made to
define seed-producing areas (SPA), which usually represent the most elementary
basic propagation material. SPA are natural stands or plantations, with good accessibility to the trees and their crowns, high productivity and low periodicity in seed
production, high specific purity in the case of possible inter-specific hybridization,
and with a mode of trees of good phenotype. The objective of the SPA is the provision of seeds from a known provenance. A thinning that eliminates undesirable
individuals (i.e., unhealthy, phenotypically diminished) will lead to the formation of
a seed stand (SS). This new basic propagation material already involves genetic
gain, even when it is based on light phenotypic selection.
The next step is the establishment of seed orchards (SOs), which are plantations
made with selected genetic material and with the specific purpose of producing
seeds for the plantation program. Clonal SOs are often the core product of the first
cycle of a high-intensity breeding program and require mastering the vegetative
propagation technique by grafting or rooting of cuttings. Progeny SOs allow dispensing with vegetative propagation, which is important to simplify the process and
occasionally crucial since in some species the percentage of success is very low (or
null) or depends on the genotype. In a low-intensity strategy, these progenies will be
the product of open pollination of the selected mothers. Thus, progeny orchards will
have greater genetic diversity than clonal orchards, which may be a particularly
sought-after effect if the goal is to increase adaptability rather than productivity.
However, open pollination involves the inclusion of many undesirable genes, leading to the need to test individuals in the orchard. In this way, the same group of trees
is a progeny trial and, simultaneously, the future seed orchard, which will only be
established when the genetic thinning prescribed by the trial evaluation is carried out.
However, monitoring and evaluating a progeny trial often exceed the possibilities
of a low-intensity breeding strategy. Gene source plantations (GSP) have been proposed as an alternative to progeny SO (Lindgren 2000). These are plantations established with seedlings from open pollinated selected trees, usually mass selected in
previous plantations or directly in the natural forest. They may be established in a
similar fashion to regular plantations and may serve concurrently several functions,
such as production of desirable commercial products, conservation of the genetic
diversity of the species, and as a local demonstration plot or as seed source for plantations, while retaining options to initiate a more regular improvement program. If
it will effectively function as a seed source, it should be thinned aiming to eliminate
undesirable individuals. The original material should include the seed of a high
number of mothers, since an intense thinning of their progeny could leave a limited
number of families in the GSP, thus favoring inbreeding.
Summarizing, recurrent selection cycles with recombination and infusions of
new material typical of high-intensity breeding are replaced, in low-intensity breeding, by linear chains leading to the development of a program with a predicted end
(Fig. 1.5). This does not mean that if the demand for seeds for productive or restoration purposes increases more than expected, the initial low-intensity program cannot be reformulated toward a new improvement cycle, moving in this case to a
classic high-intensity program.
M. J. Pastorino