Agriculture Reference
In-Depth Information
South Africa. The papayas can enter into production as early as 6-8 months after
planting, and provide a high potential yield of 60-100 t/ha per year (Chan
2009
).
However, pollination, fruit set and production are closely related to sex expression
that is highly dependent on genotype-environment interactions (Nakasone and Paull
1998
). Hawaii has become the pioneer country for commercial cultivation both in
providing modern commercial techniques (Yee
1970
) and in developing commer-
cial transgenic papayas with coat-protein mediated resistance to Papaya Ring Spot
virus (PRV) (Gonsalves
1998
). The key for successful cultivation under subtropical
conditions not only lays in the possibility of obtaining high yields but also high
content of soluble solids all year round and particularly during the coldest months.
Reproductive Biology
Carica papaya
is the only polygamous species of the genus
Carica
(Badillo
1971
).
Following a short juvenile period, in which only leaves are formed, papaya flow-
ers are borne in modified cymose inflorescences located in the axil of these leaves.
The type of inflorescence depends upon the sex of the tree and the type of flowers
present. The structure of the flower allows for easy pollination by wind and insects.
Inflorescence and Fruit Development
Three main flower types are produced in papaya: staminate or male (♂), hermaph-
rodite (H) and female, (♀) but numerous intermediate flower types can be observed,
which have been summarised and simplified by Storey (
1958
) into eight categories,
borne in three tree forms: male, hermaphrodite and female (Table
5.3
).
In the tropical regions of the world, hermaphrodite trees are preferred for their
higher productivity since every tree will produce commercial fruits. However, in
subtropical regions, where cool winters are likely, female flower production is
preferred for local markets because such flowers are stable at low temperatures.
Hermaphrodite flowers tend to fuse their anthers with the carpels and produce de-
formed carpellodic fruits. Hermaphrodite flowers, which can give rise to the most
preferred of commercial fruits, are largely cleistogamous with anthers dehiscing
and releasing the pollen to effect self-pollination prior to anthesis (Rodríguez Pastor
et al.
1990
). Parthenocarpic seedless fruits are not commercially used due to their
small adult tree size and the presence of bitter tiny underdeveloped embryos that
sometimes occur in isolated female trees without any close pollen source (Chan
2009
). This explains why commercial lines are usually gynodioecious presenting
only female and hermaphrodite plants.
Commercial production usually requires the planting of 3-4 plants per hole to
ensure the maximum number of gynodioecious plants. Undesirable plants are re-
moved after the first flower is produced. According to the genetic makeup of papaya
elucidated by Storey (
1953
), appropriate crossings (H × H) planted at 4 plants per
