132
providing a first approach to the analysis of the genetic diversity of a species. A
generalized interpretation of the genotype-environment relationship will make it
possible to discern whether the type of variation is clinal, i.e., gradually changing
characters, or ecotypical, that is, variation occurring in discrete changes of the character (it does not correspond to a gradual change of the environmental conditions).
However, the establishment of common garden experiments is needed to distinguish
between environmental and genetic effects. To accomplish this, breeding the bulk
progeny of several natural populations in a common location is a further step on the
way to unravel the genetic patterns of a species. Yet, a next step can be advanced if
we keep the identification of the parental relationships of those progenies assayed.
The analysis of variation of quantitative traits in progeny trials allows us to estimate
the genetic variation within and between populations.
Out of the two species considered in this chapter, N. pumilio is the one with more
breeding potential, due to its better productivity and forestry shape. Additionally,
the interest on cultivating these species is higher in N. pumilio due to the fact that it
lacks the ability to resprout from the stumps, thus making its cultivation for restoration purposes more necessary than in N. antarctica. Consequently, there are more
advances in quantitative genetics of N. pumilio, which will be presented below following the three levels of analysis: (1) in situ geographic variation, (2) among populations’ variation in common garden trials, and (3) genetic variation by means of
progeny trials.
5.5.1 In Situ Geographic Variation
Variation in seed traits across environmental gradients could evidence adaptive processes. Aiming to analyze this possibility, Mondino (2014) collected seeds in 14
natural populations of N. pumilio in the Province of Chubut (a small portion of the
wide Argentine distribution of the species), representing a latitudinal range of 2
degrees and a precipitation range from 400 to 1000 mm of annual average. The
mean weight of 100 seeds was 1.36 g, and differences among populations were
shown by means of an ANOVA for weight, width, length, and length/width ratio of
the seeds (80.6% of the total variance was explained by population in the weight
trait). However, it was not possible to recognize a consistent pattern associated with
the two environmental characters considered (different interactions were shown
between precipitation and latitude factors depending on the trait).
Based on a new seed collection in six populations, now representing three altitudinal levels in two sites (Mondino 2014), interaction between altitude and sites was
shown for 100-seed weight (the highest population produced the heaviest seeds in
one site, while the opposite was verified in the other). A different picture was found
for seed-shape traits, where those of the highest altitude were the narrowest in
both sites.
C. Soliani et al.
providing a first approach to the analysis of the genetic diversity of a species. A
generalized interpretation of the genotype-environment relationship will make it
possible to discern whether the type of variation is clinal, i.e., gradually changing
characters, or ecotypical, that is, variation occurring in discrete changes of the character (it does not correspond to a gradual change of the environmental conditions).
However, the establishment of common garden experiments is needed to distinguish
between environmental and genetic effects. To accomplish this, breeding the bulk
progeny of several natural populations in a common location is a further step on the
way to unravel the genetic patterns of a species. Yet, a next step can be advanced if
we keep the identification of the parental relationships of those progenies assayed.
The analysis of variation of quantitative traits in progeny trials allows us to estimate
the genetic variation within and between populations.
Out of the two species considered in this chapter, N. pumilio is the one with more
breeding potential, due to its better productivity and forestry shape. Additionally,
the interest on cultivating these species is higher in N. pumilio due to the fact that it
lacks the ability to resprout from the stumps, thus making its cultivation for restoration purposes more necessary than in N. antarctica. Consequently, there are more
advances in quantitative genetics of N. pumilio, which will be presented below following the three levels of analysis: (1) in situ geographic variation, (2) among populations’ variation in common garden trials, and (3) genetic variation by means of
progeny trials.
5.5.1 In Situ Geographic Variation
Variation in seed traits across environmental gradients could evidence adaptive processes. Aiming to analyze this possibility, Mondino (2014) collected seeds in 14
natural populations of N. pumilio in the Province of Chubut (a small portion of the
wide Argentine distribution of the species), representing a latitudinal range of 2
degrees and a precipitation range from 400 to 1000 mm of annual average. The
mean weight of 100 seeds was 1.36 g, and differences among populations were
shown by means of an ANOVA for weight, width, length, and length/width ratio of
the seeds (80.6% of the total variance was explained by population in the weight
trait). However, it was not possible to recognize a consistent pattern associated with
the two environmental characters considered (different interactions were shown
between precipitation and latitude factors depending on the trait).
Based on a new seed collection in six populations, now representing three altitudinal levels in two sites (Mondino 2014), interaction between altitude and sites was
shown for 100-seed weight (the highest population produced the heaviest seeds in
one site, while the opposite was verified in the other). A different picture was found
for seed-shape traits, where those of the highest altitude were the narrowest in
both sites.
C. Soliani et al.