138
gain by a more efficient photosynthetic performance (e.g., Premoli and Brewer
2007; Molina-Montenegro et al. 2012) and the efficient allocation of non-structural
carbohydrates (e.g., Fajardo et al. 2013).
The dissimilar results thrown by the two last essays may be due to the different
ages of evaluation, what was evidenced by the lack of age-to-age correlation in the
second and longer trial. Alternatively, differences could be related to the sampling
sites. In the first case, the contrasting morphotypes were vegetating close to each
other, and consequently gene flow likely exists among them, thus restricting differentiation and consequently adaptation. On the contrary, in the second study, both
morphotypes are separated by a relatively large distance, and gene flow is likely
more limited than in the first case, and therefore adaptation is more probable.
Based on the previous results, altitudinal and latitudinal zonation should be considered in the definition of management units and/or in the delineation of provenance regions in N. pumilio, although not in a clinal way, since ecotypic variation
seems to prevail. The seed sources for restoration programs, as well as the seed
orchards for low-intensity breeding, should avoid the admixture of genetic materials
from stands markedly separated in altitude or latitude. Observed gaps in bud sprouting and growth rhythm development between provenances in both gradients evidenced adaptation to local conditions. Particular site conditions should not be
dismissed in active restoration. On the other hand, the amount of annual precipitation does not seem to make a difference among populations.
5.5.3 Genetic Variation by Means of Progeny Trials
A preliminary study of intra-population genetic variation (Mondino 2014) was conducted by means of a greenhouse progeny test that included the progeny of 68 openpollinated mother trees corresponding to four natural populations of the Province of
Chubut (N = 897). At the end of the first growing season, several architectural traits
were measured in each potted seedling. The dispersion of data was large due to the
low sampling level; however, the difference among populations and the significance
of the family factor could be shown for some traits. Differences among populations
were proved to be significant for height, slenderness index (height/diameter ratio),
and branchiness index (height/number of branches ratio), for which a differentiation
among populations of Q ST = 15%, Q ST = 16%, and Q ST = 17% was estimated, respectively. It must be highlighted that the differentiation was due to only one population
that was different from the other three: San Martin, which is in fact a marginal population of the steppe, completely isolated from the forest continuum (43° 49′ 47′ S,
70° 45′ 33′ W; 1350 m asl), and subjected to stressful precipitation conditions
(annual average of 300 mm). The heritability estimated for the traits whose family
factor resulted significant were mostly moderate, ranging from 0.15 to 0.57
(Table 5.5).
C. Soliani et al.
gain by a more efficient photosynthetic performance (e.g., Premoli and Brewer
2007; Molina-Montenegro et al. 2012) and the efficient allocation of non-structural
carbohydrates (e.g., Fajardo et al. 2013).
The dissimilar results thrown by the two last essays may be due to the different
ages of evaluation, what was evidenced by the lack of age-to-age correlation in the
second and longer trial. Alternatively, differences could be related to the sampling
sites. In the first case, the contrasting morphotypes were vegetating close to each
other, and consequently gene flow likely exists among them, thus restricting differentiation and consequently adaptation. On the contrary, in the second study, both
morphotypes are separated by a relatively large distance, and gene flow is likely
more limited than in the first case, and therefore adaptation is more probable.
Based on the previous results, altitudinal and latitudinal zonation should be considered in the definition of management units and/or in the delineation of provenance regions in N. pumilio, although not in a clinal way, since ecotypic variation
seems to prevail. The seed sources for restoration programs, as well as the seed
orchards for low-intensity breeding, should avoid the admixture of genetic materials
from stands markedly separated in altitude or latitude. Observed gaps in bud sprouting and growth rhythm development between provenances in both gradients evidenced adaptation to local conditions. Particular site conditions should not be
dismissed in active restoration. On the other hand, the amount of annual precipitation does not seem to make a difference among populations.
5.5.3 Genetic Variation by Means of Progeny Trials
A preliminary study of intra-population genetic variation (Mondino 2014) was conducted by means of a greenhouse progeny test that included the progeny of 68 openpollinated mother trees corresponding to four natural populations of the Province of
Chubut (N = 897). At the end of the first growing season, several architectural traits
were measured in each potted seedling. The dispersion of data was large due to the
low sampling level; however, the difference among populations and the significance
of the family factor could be shown for some traits. Differences among populations
were proved to be significant for height, slenderness index (height/diameter ratio),
and branchiness index (height/number of branches ratio), for which a differentiation
among populations of Q ST = 15%, Q ST = 16%, and Q ST = 17% was estimated, respectively. It must be highlighted that the differentiation was due to only one population
that was different from the other three: San Martin, which is in fact a marginal population of the steppe, completely isolated from the forest continuum (43° 49′ 47′ S,
70° 45′ 33′ W; 1350 m asl), and subjected to stressful precipitation conditions
(annual average of 300 mm). The heritability estimated for the traits whose family
factor resulted significant were mostly moderate, ranging from 0.15 to 0.57
(Table 5.5).
C. Soliani et al.