Agriculture Reference
In-Depth Information
with healthy areas that turn bulky (Fig.
6.4d
,
e
). Albedo cells are tubular in shape
and those lining the cracks separate at the middle lamella leaving like-protruding
stumps. This separation sometimes takes place with no damage to the cells so that
cells retain their turgor, but many cells are irreparable damaged, lose their turgor
and wall collapses.
The cause of
creasing
is not yet clearly understood. Climatic factors, cultural
practices and endogenous factors have been related with this physiological disorder.
A number of mineral elements have been also related to
creasing
, with molybdenum
(Mo) being of critical importance.
Creasing
has been connected with pectin degradation, loosening the connection
among the cells of the albedo tissue. Promotion of pectinmethylesterase activity of
albedo tissue of creased fruit has been demonstrated and also a significant increase
on the amount of water-soluble pectins. It is suggested that molybdenum acts as a
co-factor in ureide synthesis, required in the formation of galacturonic acid, a major
component of pectins.
The application of GA
3
(10-20 mg l
−1
) at early stages of fruit development or
just prior to fruit colour-break reduce considerably the incidence of
creasing
. As for
puffiness
, the addition of nitrogen compounds reinforces its effect. It had a strong
inhibition effect on colour development when applied close to colour-break.
Navel Rind Stain
Fruits of Navel oranges are very susceptible to rind breakdown. Initially, injured
fruits show small depressions on the rind with no changes in colour and retain their
intact oil glands. The disorder begins at the flavedo-albedo union area, where the
cells become dehydrated and flattened, and finally die (Fig.
6.4f
). Despite of it, the
cuticle did not show any sign of disruption or damage. When damage riches up the
flavedo and epidermis, the cells die as well and develop brown to black lesions of
necrotic depressed areas.
The cause of this physiological disorder has been related to nutritional imbal-
ances, drought and rainy periods in alternation with cold periods. The incidence
of navel rind stain varies in intensity from year to year, among orchards and even
among varieties, affecting up to 50 % of mature fruits in some cases, such as 'Nave-
late' in Spain. Fruit position on the tree has shown as important factor in developing
rind breakdown, fruits outside of canopy being most sensitive fruits and the outside
face of fruit being more sensitive than the inside face. In 'Navelate' oranges stored
at 20ºC, transference of fruit from low (45 %) to high (95 %) RH starts or aggravates
the incidence of this disorder.
Nowadays we have not effective treatments to control it. However, rootstock
plays an important influence in the development of the disorder. Carrizo citrange is
more susceptible than Cleopatra mandarin, and it, in turn, more than sour orange.
This dependence has been related to rootstock influence on water transpiration ca-
pacity, supported by the histological study of fruit peduncle.
