Agriculture Reference
In-Depth Information
Climatic Requirements
Papaya is a tropical crop that requires high temperatures to produce good quality
fruits all year round. After a brief juvenile phase, vegetative growth coincides with
flower development and an inflorescence emerges in the axil of each leaf, provided
climatic and cultural factors are adequate. Temperatures below 20 °C have nega-
tive effects that can cause, among other problems, carpeloidy, sex changes, reduced
pollen viability and low sugar content of the fruit, the latter factor being of criti-
cal importance in marketing papayas. Furthermore, if the temperature falls below
12-14 °C for several hours, papaya production can be severely affected particularly
in dioecious cultivars (Nakasone and Paull
1998
). Temperatures higher than 35 °C
favour sex reversal phenomena with hermaphrodite flowers changing to functional
male flowers that do not produce fruits of commercial quality (Chan
2009
).
Thus, in theory, the papaya can only thrive in a stable tropical climate, and, even
then, cultural practices should be optimised to maintain a high constant growth rate
throughout the entire life of the plant in order to achieve maximum yields. Modern
protected cultivation is the solution of choice for the mild subtropics (Galán Saúco
and Rodríguez Pastor
2007
) such as in the Canary Islands, where over 250 ha of pa-
paya (around 90 % of the total papaya plantings) are currently grown in greenhouses
and additional plantings are planned for the near future. Commercial greenhouse
cultivation is also carried out in Japan, with around 10 ha (about 30 % of total plant-
ings) and Israel with 10 ha (100 % of total plantings). In addition to provide a suit-
able growing environment, greenhouse production of papaya also offers protection
from the aphid vectors of Papaya Ringspot Virus (PRV), a most serious commercial
threat against which only transgenic papaya cultivars have shown acceptable resis-
tance. The fact that transgenic papayas are, at present, only approved for marketing
in USA, Canada and Japan (Anon
2012
) gives special relevance to greenhouse pro-
duction of this crop. Papayas are very sensitive to wind damage and can be uprooted
at wind speeds higher than 64 km/h but, even at lower wind speeds, partial defolia-
tion can reduce both photosynthesis potential and total soluble solids (TSS) content
of the fruits. Both problems can also be avoided by greenhouse cultivation. Papaya
is a continuous fruit producing plant that responds to a regular, uniform watering and
prefers an annual precipitation rate of around 1,200 mm. It has been reported that
irrigation can increase yield by 20 % over naturally rain fed papayas in Malaysia,
which can more than compensate for the cost of the irrigation system (Chan
2009
).
Crop Management
The cultivation of papaya as a backyard tree in home gardens has always been very
popular in many tropical and subtropical countries but, more recently, in the twenti-
eth century, papaya has become an important commercial crop in countries such as
Hawaii in the US, Mexico, Malaysia and Brazil. Many attempts have been made to
breed papayas to suit the subtropical conditions in places like Australia, Israel and
