381
The F v /F m ratio represents the maximum efficiency of the photosystem II; a low
value of F v /F m indicates an inefficient use of the absorbed energy and photoinhibition (Murchie and Lawson 2013). The F v /F m ratio decreased in C. fissilis plants
grown at 10 °C and remained with no changes in C. saltensis (Fig. 14.3). These
results indicate that although C. fissilis increased energy dissipation in the form of
heat, in the long term, this mechanism was not enough to compensate the deleterious effects of stress. Consequently, irreversible damage occurred in the photochemical stage of photosynthesis and photoinhibition.
From the results obtained on the modulated fluorescence variables, it can be
inferred that C. saltensis was able to acclimate at low temperatures, whereas C. fissilis was not. This behavior agrees with the climatic features of the home sites of
both species. It suggests that photosynthesis of C. saltensis from Yungas (Calilegua
provenance), with minimum temperatures of 12 °C, is more tolerant to low temperatures than photosynthesis of C. fissilis from Alto Paraná Rainforest (San Antonio
provenance), with minimum temperatures of 16 °C.
The leaves of C. saltensis grown at 10 °C showed higher concentrations of quercitol and catechin than those grown at 25 °C. Contrary to C. saltensis, in response
to low temperatures, C. fissilis kept the concentrations of quercitol and catechin
with no changes (Fig. 14.3).
It can be concluded that C. saltensis, with a higher altitudinal niche than C. fissilis, is more tolerant to low temperatures, since it has a stable photosynthesis and
the ability to synthesize cryoprotectants in these environmental conditions.
Interspecific variation of water stress tolerance in the genus was also studied
(Ruiz et al. 2013). It is well known that the seedling stage is the most critical for
trees development (Garkoti et al. 2003), because its limited root system is more
vulnerable to water shortage. The understanding of seedling adaptive physiological
responses to drought is relevant to predict potential areas of cultivation. The aim of
this work was to study the physiological response in greenhouse conditions of seedlings of C. balansae, C. balansae × C. saltensis hybrid (average annual rainfall
below 1000 mm at their home sites), and C. fissilis, (average annual rainfall above
2000 mm) under different simulated water regimes. Two provenances of C. balansae (Río Seco and Yuto), one provenance of the hybrid (Pintascayo), and two provenances of C. fissilis (San Antonio and Guaraní) were submitted to four simulated
rainfall treatments: 600 mm/year, 800 mm/year, 1000 mm/year, and 1200 mm/year.
This factorial trial was installed in Famaillá Experimental Station of INTA (27° 3’
S, 65° 25’ W, 450 m asl) with a completely randomize design of 15 replications
(N = 300). One seed per pot was sown in January; pots were 13 cm in diameter and
45 cm in deep and were filled with a local loamy soil. After sowing, the pots were
transferred to a greenhouse in order to exclude the natural rainfall. The pots were
maintained close to field capacity until the beginning of simulated rainfall treatments and were rotated regularly in their positions to avoid confounding effects of
light and temperature gradients. With seedlings emerged, rainfall treatments were
applied from March to December, and, from August onward, leaf relative water
content (RWC) and water potential (Ψ w ) were measured. The RWC was calculated
according to the following equation:
14 Breeding Strategy for the Cedrela Genus in Argentina
The F v /F m ratio represents the maximum efficiency of the photosystem II; a low
value of F v /F m indicates an inefficient use of the absorbed energy and photoinhibition (Murchie and Lawson 2013). The F v /F m ratio decreased in C. fissilis plants
grown at 10 °C and remained with no changes in C. saltensis (Fig. 14.3). These
results indicate that although C. fissilis increased energy dissipation in the form of
heat, in the long term, this mechanism was not enough to compensate the deleterious effects of stress. Consequently, irreversible damage occurred in the photochemical stage of photosynthesis and photoinhibition.
From the results obtained on the modulated fluorescence variables, it can be
inferred that C. saltensis was able to acclimate at low temperatures, whereas C. fissilis was not. This behavior agrees with the climatic features of the home sites of
both species. It suggests that photosynthesis of C. saltensis from Yungas (Calilegua
provenance), with minimum temperatures of 12 °C, is more tolerant to low temperatures than photosynthesis of C. fissilis from Alto Paraná Rainforest (San Antonio
provenance), with minimum temperatures of 16 °C.
The leaves of C. saltensis grown at 10 °C showed higher concentrations of quercitol and catechin than those grown at 25 °C. Contrary to C. saltensis, in response
to low temperatures, C. fissilis kept the concentrations of quercitol and catechin
with no changes (Fig. 14.3).
It can be concluded that C. saltensis, with a higher altitudinal niche than C. fissilis, is more tolerant to low temperatures, since it has a stable photosynthesis and
the ability to synthesize cryoprotectants in these environmental conditions.
Interspecific variation of water stress tolerance in the genus was also studied
(Ruiz et al. 2013). It is well known that the seedling stage is the most critical for
trees development (Garkoti et al. 2003), because its limited root system is more
vulnerable to water shortage. The understanding of seedling adaptive physiological
responses to drought is relevant to predict potential areas of cultivation. The aim of
this work was to study the physiological response in greenhouse conditions of seedlings of C. balansae, C. balansae × C. saltensis hybrid (average annual rainfall
below 1000 mm at their home sites), and C. fissilis, (average annual rainfall above
2000 mm) under different simulated water regimes. Two provenances of C. balansae (Río Seco and Yuto), one provenance of the hybrid (Pintascayo), and two provenances of C. fissilis (San Antonio and Guaraní) were submitted to four simulated
rainfall treatments: 600 mm/year, 800 mm/year, 1000 mm/year, and 1200 mm/year.
This factorial trial was installed in Famaillá Experimental Station of INTA (27° 3’
S, 65° 25’ W, 450 m asl) with a completely randomize design of 15 replications
(N = 300). One seed per pot was sown in January; pots were 13 cm in diameter and
45 cm in deep and were filled with a local loamy soil. After sowing, the pots were
transferred to a greenhouse in order to exclude the natural rainfall. The pots were
maintained close to field capacity until the beginning of simulated rainfall treatments and were rotated regularly in their positions to avoid confounding effects of
light and temperature gradients. With seedlings emerged, rainfall treatments were
applied from March to December, and, from August onward, leaf relative water
content (RWC) and water potential (Ψ w ) were measured. The RWC was calculated
according to the following equation:
14 Breeding Strategy for the Cedrela Genus in Argentina