Agriculture Reference
In-Depth Information
into a network supplying the seeds and the pericarp. The torus (receptacle) is the
structure at the base of the pedicel.
Grape berries carry up to four seeds. These seeds contain an embryo, endosperm
(a nutrient supply) and the seed coat. Greater seed number and larger seeds are
often associated with larger berries and this is thought to be due to the stimulation
of cell mitosis in response to the release of hormonal signals from the seeds (Ojeda
et al.
1999
). The demand for seedless but large table grapes by consumers can be
addressed by the application of gibberellin at flowering or fruit set which increases
the sink strength of the berries. Seed development is influenced by climatic condi-
tions, vine water status and management practices such as pruning.
Berry Growth
The grape berry is classified as a non-climacteric fruit as it does not show an in-
crease in respiration with ripening. Complex interactions of hormones appear to be
involved in berry ripening including declines of indole acetic acid and increases in
abscisic acid, the brassinosteroid castasterone and ethylene (Chervin et al.
2004
;
Davies et al.
1997
). Berry growth follows a double sigmoidal pattern (Coombe
1992
) entailing two stages of rapid growth (Mullins et al.
1992
). During late ripen-
ing a third stage characterised by berry shrinkage is evident in some varieties. The
first 10 days after fertilization, are characterised by rapid cell division and this is
followed by cell enlargement which lasts 40-60 days (Harris et al.
1968
) depend-
ing on temperature and other environmental parameters. Organic acids, tannins and
hydroxycinnamates accumulate and seed enlargement also occurs during this stage
(Pratt
1971
). Following the first stage of rapid growth is a lag period that can last
anywhere from 7 to 40 days. During the second phase of growth berries begin to
soften, lose chlorophyll and, in red varieties, will undergo a colour change. Verai-
son is the term referred to as 'berry softening'. This rapid stage of growth can last
anywhere from 35 to 55 days and is accompanied by cell wall metabolism that
encourages cell expansion (Ojeda et al.
1999
). Maximum berry weight is obtained
approximately 95 days after flowering, and depending on irrigation practice and
variety can range between 0.5 and 2.5 g on a fresh weight basis at harvest. Sugars
and volatile aromas accumulate during this stage and acid concentrations decrease.
During the final stage of development, berry weight may plateau or decline (Mc-
Carthy
1999
) and further changes in flavours and aromas occur.
Determinants of Berry Volume
Irrigation and vine water status can have a significant impact on berry size. Water
stress between flowering and veraison can decrease berry size and this is often ir-
reversible (van Zyl
1984
; Matthews et al.
1987
) possibly because this is when cell
division occurs and cell number per berry is determined. Nutritional deficiencies
