Agriculture Reference
In-Depth Information
Peel Disorders Linked to Fruit Senescence
In the marketing of citrus for fresh consumption an oversupply often occurs, with
a consequent fall in price. It is the case of Clementine mandarins, for which it is of
the utmost importance to extend the picking season and so the market. But the on-
tree storage of fruit up to its plain maturity leads to the appearance of physiological
disorders linked to peel senescence, such as discoloration, stains and blemishes that
diminish fruit quality (Fig.
6.4g
,
h
). After plain maturation high temperature and
high relative humidity accelerate the process.
Some of these disorders can be partially controlled by applying gibberellins.
The application of 5 mg l
−1
of GA
3
prior to fruit colour-break is enough to delay the
peel senescence for more than 30 days with a consequent delay on the appearance
of peel disorders linked to the process. As for other physiological disorders related
to peel tissue nitrogen compounds are known to enhance the effectiveness of GA
3
.
Such treatments do not affect internal fruit characteristics, which is particularly
important for Clementine mandarins; however this group of mandarins loses the
juice progressively after fruit colour-break, and GA
3
treatment does not stop it;
consequently, 30-50 days after treatment it is possible to pick fruits of high external
quality but with very low juice content
Fruit Abscission
Fruit of navel oranges and of some hybrids are prone to abscission as soon as they
overcome the maturation process (Fig.
6.4i
). Applying synthetic auxins can effi-
ciently control this process. The application of 2,4 DP (15 mg l
−1
) delays signifi-
cantly fruit abscission of navel oranges. Treatments must be carried out prior to the
abscission process. Those applied 1 month before colour-break have shown effica-
cious retarding fruit abscission of 'Navelate' sweet orange for more than 5 months.
Repetition of such treatment 2 months later has no additional effect except if more
than 5 months of on tree storage is requested.
Internal fruit characteristics are not altered by these treatments; however, since
treatments are applied to delay harvesting, rind disorders associated to senescence
must be prevented by GA
3
. The delay of harvest time reduces the intensity of
the next flowering and that must be taken into account, especially in the case of
alternate bearing varieties.
Plant Nutrition and Fertilization
Mineral nutrition of citrus has been extensively studied. This subject, actually, in-
volves five macronutrients (N, P, K, Ca and Mg), and some micronutrients that
influence and often limit fruit production. See reviews by Agustí (
2003
), Davies and
