363
13.2.4 Clonal Seed Orchards of Cedrela balansae and Cedrela
angustifolia: Molecular Genetic Bases
Seed orchards are the most common and cost-effective means of making available a
stable supply of genetically improved seeds (Ipinza and Vergara 1998; Varghese
et al. 2000). The optimal function of clonal seed orchards (CSO) depends on many
factors; the genetic purity of the clones to be included in the orchard is a crucial
starting point.
As was described in the present chapter, our work allowed us to detect genetically pure C. balansae populations from those containing a significant proportion of
trees that harbor genetic contributions of both C. balansae and C. saltensis parental
species. Consequently, Acambuco and Pintascayo populations were discarded to
comprise the C. balansae CSO. In addition, all clones to be included should have a
purity ≥99%, according to genetic assignment analysis by AFLP markers.
In long-term breeding programs, the intensity of selection applied over breeding
populations to build up seed orchards with superior genotypes restricts the number
of genotypes involved in the final orchard, thereby decreasing genetic diversity and
increasing the risk of inbreeding depression over successive generations. To balance
genetic gains and diversity, genomic diversity parameters through the employment
of molecular markers represent a valuable tool as selection criteria (Marcucci Poltri
et al. 2003; Zelener et al. 2005). Accordingly, for the optimal design of C. balansae
CSO, a genome analysis of 51 superior individuals selected from C. balansae breeding population – showing a purity ≥99% – was carried out (Soldati et al. 2015). To
characterize the levels of genetic diversity, to estimate the rates of inbreeding (Fis),
and to determine the genetic similarities and relationships between selected individuals, seven polymorphic SSRs (Soldati et al. 2014a) and two AFLPs markers
combinations (Soldati et al. 2013) were used.
Genetic diversity was moderate to high (He = 0.716 from SSR and He = 0.269
from AFLP markers) and similar to average genetic diversity found in natural populations of the species (He = 0.618 from SSR and He = 0.222 from AFLP markers;
Soldati et al. 2013) suggesting that selected individuals for the CSO are representative samples of the breeding population. In addition, no significant grouping of individuals either by families or by geographical origins was observed, which is
consistent with results obtained for the natural populations studied; as was previously mentioned, C. balansae populations could behave as a homogeneous genetic
unit in the Yungas. However, low average similarity index (0.229 and 0.521 for SSR
and AFLP markers, respectively) between individuals and low rates of inbreeding
(Fis = 0.12, SSRs) were detected. Therefore, inbreeding levels for the proposed
CSO could be considered as acceptable.
The absence of interspecific hybridization between C. angustifolia and C. saltensis or between C. angustifolia and C. balansae, described in this chapter and
reported by Zelener et al. (2016), suggests that all individuals of C. angustifolia
breeding population are genetically pure; therefore, no CSO purification is required.
Accordingly, a genome analysis of 44 superior individuals from breeding
13 Patterns of Neutral Genetic Variation for High-Value Cedar Species…
13.2.4 Clonal Seed Orchards of Cedrela balansae and Cedrela
angustifolia: Molecular Genetic Bases
Seed orchards are the most common and cost-effective means of making available a
stable supply of genetically improved seeds (Ipinza and Vergara 1998; Varghese
et al. 2000). The optimal function of clonal seed orchards (CSO) depends on many
factors; the genetic purity of the clones to be included in the orchard is a crucial
starting point.
As was described in the present chapter, our work allowed us to detect genetically pure C. balansae populations from those containing a significant proportion of
trees that harbor genetic contributions of both C. balansae and C. saltensis parental
species. Consequently, Acambuco and Pintascayo populations were discarded to
comprise the C. balansae CSO. In addition, all clones to be included should have a
purity ≥99%, according to genetic assignment analysis by AFLP markers.
In long-term breeding programs, the intensity of selection applied over breeding
populations to build up seed orchards with superior genotypes restricts the number
of genotypes involved in the final orchard, thereby decreasing genetic diversity and
increasing the risk of inbreeding depression over successive generations. To balance
genetic gains and diversity, genomic diversity parameters through the employment
of molecular markers represent a valuable tool as selection criteria (Marcucci Poltri
et al. 2003; Zelener et al. 2005). Accordingly, for the optimal design of C. balansae
CSO, a genome analysis of 51 superior individuals selected from C. balansae breeding population – showing a purity ≥99% – was carried out (Soldati et al. 2015). To
characterize the levels of genetic diversity, to estimate the rates of inbreeding (Fis),
and to determine the genetic similarities and relationships between selected individuals, seven polymorphic SSRs (Soldati et al. 2014a) and two AFLPs markers
combinations (Soldati et al. 2013) were used.
Genetic diversity was moderate to high (He = 0.716 from SSR and He = 0.269
from AFLP markers) and similar to average genetic diversity found in natural populations of the species (He = 0.618 from SSR and He = 0.222 from AFLP markers;
Soldati et al. 2013) suggesting that selected individuals for the CSO are representative samples of the breeding population. In addition, no significant grouping of individuals either by families or by geographical origins was observed, which is
consistent with results obtained for the natural populations studied; as was previously mentioned, C. balansae populations could behave as a homogeneous genetic
unit in the Yungas. However, low average similarity index (0.229 and 0.521 for SSR
and AFLP markers, respectively) between individuals and low rates of inbreeding
(Fis = 0.12, SSRs) were detected. Therefore, inbreeding levels for the proposed
CSO could be considered as acceptable.
The absence of interspecific hybridization between C. angustifolia and C. saltensis or between C. angustifolia and C. balansae, described in this chapter and
reported by Zelener et al. (2016), suggests that all individuals of C. angustifolia
breeding population are genetically pure; therefore, no CSO purification is required.
Accordingly, a genome analysis of 44 superior individuals from breeding
13 Patterns of Neutral Genetic Variation for High-Value Cedar Species…