Agriculture Reference
In-Depth Information
Flowering and Fruit Set
The development of individual flowers commences at bud-break, and by anthesis
the total number of flowers per inflorescence typically ranges between about 100
and 400. However, this may extend to over a 1,000 for some cultivars, or to just a
few flowers for intermediate tendril and inflorescence forms. Air and soil tempera-
ture treatments applied at the time of bud-break can induce a 10-25 % variation
in the number of flowers formed on an inflorescence, and demonstrate a mecha-
nism through which weather conditions in early spring can have a direct influence
on yield formation (Petrie and Clingeleffer
2005
; Field et al.
2009
; Rogiers et al.
2011b
). Other factors that can influence the number of flowers per inflorescence in-
clude rootstock, position of the inflorescence on the shoot and pruning system. Vine
carbohydrate reserve status can also alter inflorescence flower numbers (Bennett
et al.
2005
), although for all of these factors it may be difficult to separate effects on
inflorescence primordia branching in the season of initiation from effects on flower-
ing formation in the subsequent spring (Dunn and Martin
2007
).
Anthesis commences with the shedding of the first flower caps or calyptra some
6-10 weeks after bud-break depending on climatic conditions and cultivar, and will
continue for approximately a week until all of the flowers on the inflorescence
have opened. Typically 20-30 % of flowers will develop into normal berries, but
this figure can be as low as 15 % or as high as 60 % and vary according to cultivar,
cultural practice and weather conditions during flowering (May
2004
). The opti-
mum temperatures for cap-fall and pollination occur between 20 and 30 °C, while
temperatures above 35 °C are detrimental. At temperatures below 15-17 °C flower
caps do not open at all, and through extended periods of cold and wet weather, the
number of successfully fertilized berries can be substantially reduced. Fruit set is
also highly dependent on an adequate supply of carbohydrates, and can be reduced
by competition with excessively vigorous shoots, from other flowers on large inflo-
rescences, or even concurrent storage of carbohydrate reserves in perennial tissues
(Rogiers et al.
2011b
).
Berry Morphology
The grape berry develops from the fertilised ovary and is composed of the seeds,
flesh and skin. The flesh is comprised of cells containing large water-filled vacuoles
that accumulate fructose and glucose, and small quantities of malic and tartaric ac-
ids. The skin is referred to as the exocarp and consists of an inner hypodermis and
outer epidermis and this is covered in a waxy cuticle which prevents desiccation and
offers resistance against pathogens (Possingham et al.
1967
). Stomata are present
on the surface of the berry but they become occluded with wax and are non-func-
tional shortly after flowering (Blanke and Leyhe
1987
). The pedicel of the berry
(berry stalk) connects the berry to the bunch stalk (rachis) and contains six vascular
bundles (Mullins et al.
1992
). The vascular bundles entering the berry branch out
