Agriculture Reference
In-Depth Information
Fruit Development
Fruits originate from ovary development (true fruit), as in stone-fruit and vines, or
from the hypanthium (false fruits), as in pome-fruits. In general, fruit development
is associated with seed fertilization and development, with the exception of parthe-
nocarpic fruit species. Two main models for fruit growth can be found with a single
or a double sigmoid dynamics (Fig.
4.7
). The single sigmoid pattern is characteristic
of pome-fruits, while the double sigmoid of stone-fruit and grape. Based on growth
analysis, the peach fruit development cycle has been divided into 4 main phases
called, S1, S2, S3 and S4 when the parameter used to monitor fruit development is
the fruit cross diameter. The same 4 phases can be recognized when fresh weight
(FW1, FW2, FW3 and FW4) or dry weight (DW1, DW2.DW3 and DW4) are used.
The duration of the cycle of peach fruit development is genetically controlled and it
may range from 60/70 (early ripening variety) up to 160/170 (late ripening variety)
days after full bloom (DAFB). The length of the different phases varies according to
the genotype: in general S1 is fairly constant (30 −35 DAFB) while S2 presents the
greatest variability and can be very short in the early ripening varieties up to 60/70
DAFB in late ripening ones. The length of S3 and S4 is dependent upon the time of
fruit ripening. S1 and S3 are the exponential growth phases, sustained by cell divi-
sion (S1) and enlargement (S1 and S3). S1 is strictly dependent on environmental
conditions affecting fruit density (number of cells/unit of fruit volume) at harvest as
well as final fruit size.
In peach, the cell division may lasts from 7 up to 25 DAFB, depending upon the
ripening period of the variety. The cell enlargement (S1 and S3), linked to increase
in vacuolar volume and cell wall, is accompanied by a gradual increase in intercel-
lular spaces. S2 is characterized by endocarp lignifications while S4 by the onset of
ripening. Apples and pears, displaying a simple sigmoid pattern, show two phases
of growth (S1 and S2), which can be represented by an expolinear model enabling
to make predictions at an early stage (40-50 days before harvest) of the final fruit
size. Parthenocarpy defines a situation in which the fruit is formed without a con-
current seed development (Fig.
4.8
). Vegetative and stimulative parthenocarpy are
recognized. In the first one, fruit development occurs naturally and is sustained by a
continuous growth of the ovary and/or accompanying tissue (hypanthium) without
any pollination. It is present in oriental persimmon and in some varieties of pear
and fig. Stimulative parthenocarpy, dependent on pollination (but not fertilization),
occurs in some grape varieties. The parthenocarpy behaviour is usually related to
high levels of auxins, gibberellins and cytokinins. The same hormones sprayed at
bloom time, may in some species, induced parthenocarpic fruit development.
Fruit Ripening
Ripening is the final stage of fruit development and is a complex physiological
syndrome, characterized by chemical and physical processes such as soluble solid
content accumulation, starch hydrolysis, decrease in acidity, flesh softening and
