Agriculture Reference
In-Depth Information
8:1. However, one male tree per 15-20 female trees provides adequate
wind pollination if male trees are located with respect to prevailing winds.
Parthenocarpy in papaya is rare. Seedless fruit or fruit with very low seeds can
be produced on female trees. These fruits are generally smaller in size. Auxins
have also been reported to induce parthenocarpic fruit.
Fruit set is no problem under open pollination in an orchard. On
hermaphrodite trees, it is most common for the terminal fl ower to set while the
laterals abscise. Under favourable conditions one or two laterals may be set and
only persist for 2-3 weeks or remain to produce undersized fruit that crowd
the fruit column. This crowding leads to fruit compaction and misshaped
fruit. Fruit thinning may be practised. The degree of compaction is due to the
peduncle length. Fruit set is variable; if lateral fl owers are not desired and only
one fruit per leaf axil is desired, set is usually 100%; if three fl owers are formed
and only one fruit is desired then the set is 33%. Annual fruit set depends upon
the length of the female sterility period in hot weather, and with one fruit per
peduncle the range is 85-95%.
Fruit
The papaya fruit is a fl eshy berry, from 50 g to well over 10 kg, and superfi cially
resembles a melon, being spherical, pyriform, oval or elongated in shape
(Fig. 11.3). Fruit shape is a sex-linked character and ranges from spherical
to ovoid in female fl owers to long, cylindrical or pyriform (pear-shaped) in
hermaphrodite fl owers. The skin of the fruit is thin and usually green when
immature, turning to yellow or orange when ripe. The fruit is normally
composed of fi ve carpels united to form a central ovarian cavity, which is lined
with the placenta, carrying numerous black seeds. Placentation is parietal,
with the seeds attached by 0.5-1 mm stalks. The seeds are dark grey to black
when mature and enclosed in a sacrotesta. The ovarian cavity is larger in
female fruit than hermaphrodite. The shape of the cavity at the transverse cut
ranges from star-shape with 5-7 furrows, to smooth and circular in shape.
In fruit development, all tissues in gynecia less than 1 mm are meristem-
atic. Later the outer layer of the epidermis increases in size while the
subepidermal layer continues to divide both anticlinally and periclinally. The
central parenchyma of the pericarp increases in size and divides, with the
placenta forming opposite the marginal vascular bundles. This meristematic
lasts 28-42 days and determines fi nal fruit size (Fig. 11.7). Fruit growth shows
two major phases. The fi rst lasts about 80 days post-anthesis, with a large
increase in dry weight occurring just before fruit maturity. Fruit development
takes 150-164 days, which is extended another 14-21 days in Hawaii in the
colder months. In subtropical areas, such as South Africa, development can
vary from 190 to 270 days (Fig. 11.2). The growth of the fl eshy mesocarp
parallels seed development and total fruit growth (Fig. 11.7).
