110
interspecific variations could be observed regarding the precise location of both
inflorescence types. In N. obliqua, nodes bearing pistillate inflorescences are consecutive to those bearing staminate inflorescences, whereas both flower types are
separated by one to several sterile nodes in the closely related species N. alpina.
Therefore, at the shoot level, a higher probability of geitonogamous self-pollination
would be expected in N. obliqua than in N. alpina (Puntieri et al. 2009).
4.6.2 Flower Phenology
The knowledge of the periods of pollen release and pistillate flowers receptivity is
highly relevant for the application of technics of manual pollination as well as for
understanding the processes conditioning seed production in natural populations. In
several Nothofagus species, including N. obliqua, the production of great amounts
of seedless fruits is common (Donoso et al. 2006a; Azpilicueta et al. 2010; Torres
et al. 2019). Factors related to such a pattern are rather unknown and may include
pollen limitation, self-interference and resource limitations, among others.
Concerning self-interference, previous observations have suggested high degrees of
overlapping between the periods of pollen release and stigma receptivity at the
shoot level (Torres and Puntieri 2013). In the cited research, the period of stigmatic
receptivity of N. obliqua was assessed through the application of manual sequential
pollination in hydroponically grown shoots.
After evaluating pollen germination on the stigmas, it could be suggested that
pistillate flowers may be receptive as soon as the expansion of their subtending
leaves allows the exposure of the stigmas to air currents. Pollen germination on the
stigmas was observed until 15 days after the anthesis of pistillate flowers, whereas
maximum pollen germination occurred between 3 and 6 days after the anthesis of
pistillate flowers. Preliminary results have shown that pollen release would be
highly dependent upon air temperature and humidity (Torres 2013). Therefore, it
could be hypothesized that the degree of temporal intra-individual overlapping
between pollen release and stigma receptivity could be linked to climatic conditions
during early shoot growth.
4.6.3 Test of Manual Pollinations
So far, there are few experimental populations of mature Nothofagus trees in
Argentina, and Nothofagus seeds are mainly collected from natural populations.
High interannual variations in flower and, therefore, seed production are typical in
several Nothofagus species, including N. obliqua. Thus, the simultaneous occurrence of high flower production in selected trees is one of the main conditioning
factors for controlled crossings.
M. M. Azpilicueta et al.
interspecific variations could be observed regarding the precise location of both
inflorescence types. In N. obliqua, nodes bearing pistillate inflorescences are consecutive to those bearing staminate inflorescences, whereas both flower types are
separated by one to several sterile nodes in the closely related species N. alpina.
Therefore, at the shoot level, a higher probability of geitonogamous self-pollination
would be expected in N. obliqua than in N. alpina (Puntieri et al. 2009).
4.6.2 Flower Phenology
The knowledge of the periods of pollen release and pistillate flowers receptivity is
highly relevant for the application of technics of manual pollination as well as for
understanding the processes conditioning seed production in natural populations. In
several Nothofagus species, including N. obliqua, the production of great amounts
of seedless fruits is common (Donoso et al. 2006a; Azpilicueta et al. 2010; Torres
et al. 2019). Factors related to such a pattern are rather unknown and may include
pollen limitation, self-interference and resource limitations, among others.
Concerning self-interference, previous observations have suggested high degrees of
overlapping between the periods of pollen release and stigma receptivity at the
shoot level (Torres and Puntieri 2013). In the cited research, the period of stigmatic
receptivity of N. obliqua was assessed through the application of manual sequential
pollination in hydroponically grown shoots.
After evaluating pollen germination on the stigmas, it could be suggested that
pistillate flowers may be receptive as soon as the expansion of their subtending
leaves allows the exposure of the stigmas to air currents. Pollen germination on the
stigmas was observed until 15 days after the anthesis of pistillate flowers, whereas
maximum pollen germination occurred between 3 and 6 days after the anthesis of
pistillate flowers. Preliminary results have shown that pollen release would be
highly dependent upon air temperature and humidity (Torres 2013). Therefore, it
could be hypothesized that the degree of temporal intra-individual overlapping
between pollen release and stigma receptivity could be linked to climatic conditions
during early shoot growth.
4.6.3 Test of Manual Pollinations
So far, there are few experimental populations of mature Nothofagus trees in
Argentina, and Nothofagus seeds are mainly collected from natural populations.
High interannual variations in flower and, therefore, seed production are typical in
several Nothofagus species, including N. obliqua. Thus, the simultaneous occurrence of high flower production in selected trees is one of the main conditioning
factors for controlled crossings.
M. M. Azpilicueta et al.