Agriculture Reference
In-Depth Information
Table 11.3.
Ideals in papaya breeding have not changed much since the following
were proposed. Additional factors have related to disease resistance (Higgins and
Holt, 1914).
Character
Tree
Vigour
Early and low fruiting - wide variation exists
Freedom from branching habits
Fruit
Productive but not compact fruiting
Small size for table use
Large size for animal feed and papain production
Uniformity in shape, symmetry and smoothness
Uniformity in ripening
Colouring before softening
Colour of
fl
esh - yellow, pink or red
Easily separable without scraping
fl
esh
Flavour - not easily described but easily recognizable
Keeping quality
Other
Papain yield
upon traditional experience and familiarity with cultivars. Total tree height
is not a good criterion to assess tree vigour, while stem diameter or girth is a
more reliable measure (Fig. 11.5). Stamen carpellody and female sterility do
not occur in dioecious cultivars.
In breeding for hermaphrodite types, selections should be evaluated
during the cool period for occurrence of stamen carpellody and again during
the warm period for female sterility. Trees that show no carpellody in winter
may show a high degree of female sterility in summer, or the opposite. Within
a specifi c locality, if temperature fl uctuations are not too wide, continual
selection and inbreeding can produce lines with minimum carpellody and
female sterility (Chan, 1984). In subtropical climates, where the range of
temperatures between summer and winter is large, dioecious cultivars are
more suitable.
Increased yields may be accomplished by increasing yields per tree, by
increasing density per unit area, or both (Hamilton, 1954). Usually only the
terminal fl ower sets fruit and others abscise or produce small, unmarketable fruit
when they set. However, lines have been observed to produce two, three or even
four normal-sized fruit on each peduncle. Multiple fruiting is strongly infl uenced
by soil fertility. Peduncles must be long enough to prevent overcrowding, which
can produce misshapen, 'pancake-like', fl at fruit. Another method to increase
production is by increasing trees per unit area. Petioles of papaya trees are
approximately 75-100 cm, or even longer, and are more or less horizontal. This
requires at least 2 m between plants in a row. A mutant 'Solo' line with very poor
yields and short petioles (45-60 cm) that are positioned obliquely upright is
available, and trees can be planted at 0.9-1.2 m apart in the row. Short, upright
