Agriculture Reference
In-Depth Information
and the cells become elongated tangentially but the inner boundary between
hypodermis and cortexmay be hard to fix(Skene,
).
Fruit colour
The colour of the fruit skin depends on its background, or ground, colour
causedbyplastidpigments,chlorophyllsandcarotenoids,andtoredcoloration
due to anthocyanins in the vacuoles.
The ground colour of immature fruits is usually dark green. As the fruit
matures one of three things may happen, dependent primarily on cultivar.
The green may fade until it has completely disappeared and the ground colour
becomes cream to pale yellow; the green may fade less completely giving a
greenish-yellow to yellowish-green ground colour; or the green may not fade.
These colour changes reflect the disappearance of chlorophyll (green) and the
unmasking or increased production of yellow carotenoids (Knee,
).
The potential for anthocyanin production is genetically determined, some
cultivarsproducingverylittleofthisevenunderthemostfavourableconditions,
others developing a deep red colour over the whole surface except under the
most unfavourable conditions, with others being intermediate. There are two
peaks of anthocyanin formation. The first, which does not result in persistent
red colour, is in fruitlets to the cell division phase. The second coincides with
the ripening of red cultivars and may continue after harvest (Figure
). The
anthocyanin pigment may be located in any or all of the outer four to six, or
even
.
, layers depending on the cultivar (Dayton,
; Pratt
et al.
,
). The
predominant anthocyanin is idaein (cyanidin-
-galactoside); others identified
are cyanidin-
-arabinoside.
The shade of red that develops depends largely on the ground colour. The
most brilliant red is produced when the ground colour is almost white and the
dullest brown when the ground colour is green (Brown,
-arabinoside and cyanidin-
).
The colour development in fruitlet skin is not persistent and so has not been
the subject of much research. Pre-harvest and immediately post-harvest red
colour development are controlled by genotype, carbohydrate supply, direct
effects of light on anthocyanin formation, temperature and nutritional factors.
Although green (e.g. 'Granny Smith') and yellow (e.g. 'Golden Delicious')
apples have a very important place in the world markets there has been con-
tinued pressure of demand for increased extent or intensity of red coloration
in those apples classed as red or part-coloured. One of the most powerful
tools in meeting this demand has been the selection of colour-sports and their
deliberate creation. Red sports are characterized by increased anthocyanin
in the mature fruits, the increase being in the epidermis, the sub-epidermal
