Agriculture Reference
In-Depth Information
several hours at 20-23 °C soil temperatures. Thus, reducing soil temperature during
the 2 months before harvest using reflective-mulch advances external ripening and
harvest date in the Clementine mandarin.
On the other hand, fruit colour-break can be also advanced by means of ethylene
releasing compounds. Although
Citrus
fruit is classified as non-climacteric fruit,
exogenous ethylene stimulates changes in fruit colour by increasing chlorophyllase
de novo
synthesis and enhancing carotenoid biosynthesis pathway genes. Spraying
100-200 mg l
−1
ethephon (an ethylene releasing compound) accelerates colouration
and thus the harvest of mandarins by 1-3 weeks. Its effectiveness depends on the
date of treatment, the best results obtained for 20-25 days before the usual date of
colour-break. An important leaf and fruit abscission may occur, with these nega-
tive effects closely related to temperature. The ethephon treatment does not change
internal fruit quality.
In
Citrus
, GA-like activity has been detected up to the onset of chlorophyll loss,
the lowest one reached at ripening. In sweet orange, fruit changes colour by re-
ducing active gibberellin concentrations (GA
1
and GA
4
) in the flavedo, which are
involved in regulating sugars and ABA accumulation and in reducing N fraction
concentration as rind colour develops. Besides, exogenous GA
3
applied prior to
colour-break delays chlorophyll degradation and reduces carotenoid concentration
in the peel. About 10-20 mg l
−1
GA
3
retards fruit colouring in 30-45 days, and
nitrogen compound such as calcium nitrate (2 %) or ammonium phosphate (1.5 %)
reinforces the effect.
Physiological Fruit Disorders
Physiological disorders are a group of disorders affecting fruit quality, sometimes
also fruit crop, which are directly related to malfunctions of fruit development
induced by environmental factors. See Agustí (
2003
), Agustí and Almela (
1991
),
Agustí et al. (
2002
;
2004
), El-Otmani (
2006
), and Petracek et al. (
2006
) for an ex-
tensive knowledge.
Splitting
Splitting
is a physiological fruit disorder manifested as a fissure of the peel, usually
developing from the stylar end and reaching, or even extending beyond, the equato-
rial zone (Fig.
6.4a
).
Splitting
is a frequent problem in oranges and mandarins all
over the world.
The causes of fruit
splitting
are not well understood, although seasonal water
deficits followed by rains during cell enlargement stage have been closely related
with the number of 'Nova' mandarin affected fruits, although in some varieties,
such as 'Ellendale' mandarin, this correlation did not apply.
Splitting
develops as a consequence of a disruption between peel and pulp
