Agriculture Reference
In-Depth Information
Fig. 6.2
Schematic representation of phenological events occurring during a 1-year develop-
mental period in
Citrus
growing under Mediterranean-type Climate.
NH
northern hemisphere,
SH
southern hemisphere
flowers and fruitlets gives rise to a massive drop of fruitlets, named physiological fruit
drop, which results in a reduced yield. Some other cultivars follow a year of heavy
fruit load (
on
year) with reduced flower production and yield (
off
year) the effect of
which depends on the length of time the fruit remains on the tree. This phenomenon is
termed
alternate bearing
and represents an important problem worldwide.
Gibberellic acid, applied at the floral bud inductive period, November-Decem-
ber in the NH (Fig.
6.2
), reduces excessive bloom problems. A concentration of
25 mg l
−1
active material at 7-8 l tree
−1
for a regular tree (sprayed by hand-gun;
25-30 atm) is recommended. Increased flowering is often very difficult to achieve.
It has been reported that paclobutrazol, an inhibitor of gibberellin biosynthesis, ap-
plied at the floral bud inductive period to the soil, at an amount of 1-10 g tree
−1
, or
as a foliar spray, at a concentration of 1,000 mg l
−1
, promotes flowering in
Citrus
.
However, its effectiveness depends on the tree crop load, and under heavy crop load
conditions fruit nullifies its effect.
Although a minimal amount of carbohydrates is required for bud sprouting and
flower initiation, neither soluble sugar content nor the accumulation of reserve car-
bohydrates seems to fulfil an inductive function; some kind of imbalance in the
nitrate-reducing mechanism in leaves has been observed in trees which are prone
to flower scarcely.
