Agriculture Reference
In-Depth Information
total soluble solids content. It has a characteristic musky fl avour and the fruit
is quite susceptible to anthracnose. 'Cibinong' is an Indonesian variety with
large red-fl eshed fruit (2-3 kg) and grown mainly for its high papain yield.
Commercial F
1
hybrids of papaya are rare, although there have been
reports of heterosis and improved yields in cross-combinations between
dif erent cultivars of papaya. Agnew (1968) described a vigorous F
1
hybrid
derived from 'Bettina 100A' and 'Petersen 170' that was, at one time,
important in Queensland. An important hybrid developed in Taiwan that has
resistance to papaya ringspot virus disease is 'Tainung No. 5'. This was derived
from a cross between 'Florida' (FL-77-5) and the 'Costa Rica Red'. In Malaysia,
an F
1
hybrid called 'Eksotika II' was developed from the hybridization of 'Line
19' with its sib, 'Eksotika' (formerly 'Line 20') (Chan, 1993). The new hybrid
has similar features to 'Eksotika', but the yield is 14-33% higher due to the
larger fruit, weighing between 600 and 800 g. The appearance of the fruit is
more attractive, with smooth skin and high tolerance to freckles. The fl esh is
fi rmer and the fruit stores longer, making 'Eksotika II' more preferred than its
predecessor for export.
The world's fi rst transgenic papaya was 'SunUp', which was transformed
with coat-protein-mediated resistance to papaya ringspot virus disease.
'Rainbow' is the fi rst transgenic commercial variety, developed from a cross
between 'SunUp' and the conventional cultivar 'Kapoho'. Transgenic varieties
of 'Kapoho' and 'Kamiya' have also been developed by introduction of the
coat-protein transgene from 'Rainbow' through conventional hybridization
and backcrossing.
Breeding
Some papaya breeding objectives are common to all regions, with objectives
specifi c to dif erent localities due to climatic dif erences, consumer preferences,
desired sex types and export markets (Table 11.3). These objectives have
changed little in the last 100 years. Desirable tree characteristics are tree
vigour, low and precocious fruiting, minimum expression of stamen carpellody
and female sterility if hermaphrodites are preferred, resistance to diseases
and insect pests, and yielding ability. Universally desired fruit characteristics
are smooth skin, free from blemishes, fi rm fruit with thick fl esh, round seed
cavity, absence of internal lumps and long shelf-life. The desired fruit size,
shape and fl esh colour may dif er in dif erent regions (Table 11.2). An extreme
example would be a preference for papaya with the heavy musky aroma in
South-east Asia, which would not be suitable in western markets. Preference
for the small (450-650 g) 'Solo' fruit is increasing in tropical countries, where
export is considered. Requirements for processing cultivars are the same,
though larger fruit may be more desirable, with size and shape being uniform
if mechanization is to be considered. Flesh colour preference is usually based
