66
narrow sense, heritability of h
2
= 0.61 must be considered as high. These results are
similar to those of studies with other forest tree species (Gallo and Geburek 1991;
Vitasse et al. 2009; Alberto et al. 2011; Premoli and Mathiasen 2011) and are evidence of a moderate adaptation to the local conditions as well as a high ability to
adapt to eventual environmental changes. From a productive point of view, the high
heritability reveals the possibility of selecting individuals that sprout early or late in
the season, depending on the selective pressure of the occurrence of late frosts
(spring) of the implantation site.
Foliar senescence started, on average, 426 days after the beginning of the previous year (March 1) and ended on April 18 (474 days), without significant differences among populations. On the other hand, the family factor resulted significant
but only explained 3.3% and 1.1% of the total variance of S 10 and S 90 , respectively,
with a low intra-population variation as estimated through the narrow sense heritabilities (h
2 S10 = 0.13; h
2 S90 = 0.07; Table 3.1). A subset (65 open-pollinated families,
373 individuals) of the above evaluated trees was measured again for the same traits
three seasons later in a climatically contrasting year (Duboscq-Carra et al. 2020).
Bud burst date (BBD), foliar senescence (FL), growing season length (GSL) and
relative height growth (RHG) were analysed. Growing degree days (GDD) and
chilling hours (CH) until bud burst were also calculated, with two possible basal
temperatures (5 °C and 7 °C) to evaluate their role in BBD. Significant differences
among populations and years in BBD and GSL were found by means of linear
mixed models, with the family factor explaining around 30% and 12% of the total
variance, respectively. In addition, differences between years but not among populations were detected for FL and for RHG. A tight relationship between GDD and CH
with BBD was found, and significant differences among populations and years were
found for both variables. Also, a high and positive correlation between the altitude
of natural populations and the mean BBD and GDD suggests that probably altitude
is conditioning thermal requirements of bud burst. Altogether these results revealed
the genetic control of bud burst and foliar senescence, but also the plasticity of these
traits, and that GDD and CH are implicated in BBD, suggesting good perspectives
to face the climate change scenario.
Stomatal density variation of preformed leaves was also analysed in this trial
(Duboscq-Carra 2019). Three leaves were measured per sapling from a subsample
of the trial (five saplings per family). Nail polish impressions from dehydrated
leaves (Brewer 1992) were taken on the abaxial surface of each leaf. Stomata were
counted under an optical microscope (Leica
®
DM500, Leica Microsystems) on a
field of view of 0.05 mm
2
with a magnification of 500x. The mean stomatal density
of the whole trial was 250 s/mm
2
, and significant differences among populations
cannot be shown. However, the family factor was significant, explaining 5% of the
total variance. The intra-population variation in this trait resulted moderate according to an estimated narrow sense heritability of h
2
= 0.21.
Several other characters were analysed in the same trial (Trial 2, Table 3.1),
including architectural, physiological, phenological, and growing traits. The general
pattern for the species in Argentina in quantitative traits resulting from these analyses (Duboscq-Carra 2019) is low differentiation and low intra-population variation,
P. Marchelli et al.
narrow sense, heritability of h
2
= 0.61 must be considered as high. These results are
similar to those of studies with other forest tree species (Gallo and Geburek 1991;
Vitasse et al. 2009; Alberto et al. 2011; Premoli and Mathiasen 2011) and are evidence of a moderate adaptation to the local conditions as well as a high ability to
adapt to eventual environmental changes. From a productive point of view, the high
heritability reveals the possibility of selecting individuals that sprout early or late in
the season, depending on the selective pressure of the occurrence of late frosts
(spring) of the implantation site.
Foliar senescence started, on average, 426 days after the beginning of the previous year (March 1) and ended on April 18 (474 days), without significant differences among populations. On the other hand, the family factor resulted significant
but only explained 3.3% and 1.1% of the total variance of S 10 and S 90 , respectively,
with a low intra-population variation as estimated through the narrow sense heritabilities (h
2 S10 = 0.13; h
2 S90 = 0.07; Table 3.1). A subset (65 open-pollinated families,
373 individuals) of the above evaluated trees was measured again for the same traits
three seasons later in a climatically contrasting year (Duboscq-Carra et al. 2020).
Bud burst date (BBD), foliar senescence (FL), growing season length (GSL) and
relative height growth (RHG) were analysed. Growing degree days (GDD) and
chilling hours (CH) until bud burst were also calculated, with two possible basal
temperatures (5 °C and 7 °C) to evaluate their role in BBD. Significant differences
among populations and years in BBD and GSL were found by means of linear
mixed models, with the family factor explaining around 30% and 12% of the total
variance, respectively. In addition, differences between years but not among populations were detected for FL and for RHG. A tight relationship between GDD and CH
with BBD was found, and significant differences among populations and years were
found for both variables. Also, a high and positive correlation between the altitude
of natural populations and the mean BBD and GDD suggests that probably altitude
is conditioning thermal requirements of bud burst. Altogether these results revealed
the genetic control of bud burst and foliar senescence, but also the plasticity of these
traits, and that GDD and CH are implicated in BBD, suggesting good perspectives
to face the climate change scenario.
Stomatal density variation of preformed leaves was also analysed in this trial
(Duboscq-Carra 2019). Three leaves were measured per sapling from a subsample
of the trial (five saplings per family). Nail polish impressions from dehydrated
leaves (Brewer 1992) were taken on the abaxial surface of each leaf. Stomata were
counted under an optical microscope (Leica
®
DM500, Leica Microsystems) on a
field of view of 0.05 mm
2
with a magnification of 500x. The mean stomatal density
of the whole trial was 250 s/mm
2
, and significant differences among populations
cannot be shown. However, the family factor was significant, explaining 5% of the
total variance. The intra-population variation in this trait resulted moderate according to an estimated narrow sense heritability of h
2
= 0.21.
Several other characters were analysed in the same trial (Trial 2, Table 3.1),
including architectural, physiological, phenological, and growing traits. The general
pattern for the species in Argentina in quantitative traits resulting from these analyses (Duboscq-Carra 2019) is low differentiation and low intra-population variation,
P. Marchelli et al.