IFEVA   02662
INSTITUTO DE INVESTIGACIONES FISIOLOGICAS Y ECOLOGICAS VINCULADAS A LA AGRICULTURA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Changes in source-sink relationships during grain-filling and its effects on sunflower root system viability and canopy functionality
Autor/es:
LISANTI, S.; J.M.CABARCOS; A.J. HALL; C.CHIMENTI
Lugar:
Mar del Plata/Balcarce
Reunión:
Conferencia; 18th International Sunflower Conference; 2012
Institución organizadora:
International Sunflower Association
Resumen:
ABSTRACT
· After flowering, grains become the main
sink for carbohydrates (C) derived from current photosynthesis or from
temporary storage, reducing the amount of (C) partitioned to the root system. During
grain filling in intact plants, size and functionality of the root system are
reduced. This suggests a trade-off
between grain formation and root viability, but other effects of grain
formation also need to be considered (e.g., altered leaf senescence, changes in
leaf photosynthetic capacity). Here we
report results from an experiment that aimed to document root and leaf
responses to a severe reduction in demand for (C) for grain formation.
· Source-sink relationships during
grain-filling were manipulated by removal of
all floral primordia at the beginning of anthesis in crops of two
sunflower (Helianthus annuus L.)
commercial hybrids of contrasting leaf senescence dynamics (Aguará 6
stay-green (SG, lower leaf senescence rate) and CF 101 fast dry down (FDD, higher leaf
senescence rate)); resulting in a factorial
experiment (repeated in two successive years) of 4 treatments: 1) SG Control:
2) SG F-; 3) FDD Control; 4) FDD F-, distributed in randomized complete
blocks (n=3). During the
grain-filling phase of the control plants, the dynamics of leaf photosynthetic
capacity (Pmax, measured at 2.000 μmol/m2.s PAR on the
uppermost expanded leaf)), LAI, organ biomass and root viability (capacity to
reduce tri-phenyl tetrazolium) in the 0-40 cm soil stratum were followed in all
treatments.
· In both years Pmax remained
stable (average value: 39.6 μmolCO2/m2.s) for 14 days
after the beginning of anthesis (DAA), and showed no significant differences
(p>0.10) between the four treatments. Pmax declined linearly as
from 14 DAA at rates (average slope = -0.84 μmolCO2/m2.s.day),
which were statistically indistinguishable between treatments.
LAI values at anthesis were statistically
indistinguishable between treatments (4.0 SG control, 4.0 FDD control, 4.2 SG
F- y 3.9 FDD F-). The SG (F-) treatment maintained the initial LAI value until
35 DAA, while the FDD (F-) treatment did so until 43 DAA, but this difference between
hybrids was not significant (p>0.10). In the control treatment both hybrids maintained
their initial LAI until 15 DAA, after which LAI declined linearly at rates
of -0.11 IAF/day in SG and -0.14 IAF/day
in FDD, which differed significantly (p < 0.05) between hybrids. The
hastening of the initiation of LAI loss in the controls with respect to the (F)
treatments was significant (p = 0.05).
Both hybrids attained, in the control treatment, their
maximum values of live root length density (LRLD) at 10 DAA, with SG reaching a
significantly (p=0.05) greater value than FDD (0.40 vs. 0.32 cm root/cm3
soil). In the (F-) treatments LRLD increased continuously until 25 DAA in both
hybrids, achieving LRLD values significantly (p=0.05) greater than those of the
(F) treatments ( + 28% greater in SG hybrid, and + 21% in FDD), but this difference between
hybrids was not significant (p>0.10).
At the end of the experiment, root dry weight (the
only organ to show major and significant responses to treatment) in the (F-)
treatment showed a 175% increase (in relation to control) in FDD and a 350% one
in SG.
· We conclude that flower primordium removal
at anthesis produces complex responses during grain filling. These clearly
included increased LRLD and root dry weight, as well as delayed loss of LAI in
the (F-) treatments. In contrast, Pmax of the uppermost expanded
leaves was not altered in these treatments. Intrinsic canopy senescence
patterns (i.e., SG vs. FDD) modulated these responses to some degree, but this
was not generalized across variables.
· For the first time, in sunflower and many
other crops, this study shows how the root system is strongly affected by (C)
reductions supply during grain-filling phase. It is a starting point to achieve
a better understanding and quantification of the potential trade-offs (in
carbohydrates and other plant resources) between grains and roots. Future
studies will require the development of quantitative response functions to
floral primordium ablation for the variables studied in these experiments as
well as for additional ones.