Ecology and Biology of Uapaca kirkiana, Strychnos cocculoides and Sclerocarya birrea in Southern Africa - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 331

open 10-14 days whereas male flowers shrivel within 3-7 days of anthesis. Male
flowers have a mild but non-distinctive scent while the female flowers have no
detectable odour. About 45% of female inflorescences abort (20.7 and 24.8%
during the bud and the anthesis stages, respectively (Ngulube, 1996).
Uapaca kirkiana fruit is described as drupaceous and borne on a thick, short
peduncle, usually less than 10 mm long. The fruits are set between January and
February and mature in August and November (Mwamba, 1995). Fruit
production varies between harvests. Fruit loads exceeding 2000 fruits per tree
have been reported in Zaire, Zambia (Mwamba, 1995) and Malawi (Akinnifesi et
al ., 2004). There is variation in fruit load between trees within populations
depending on tree size. There is also seasonal variation in fruit production within
and between populations in the miombo. The average number of fruits per tree
has also been shown to be variable between different tree sizes and even in the
same size class. Short trees with small diameters and crowns have fewer fruits
than larger trees. The physiological basis for these differences is presumably the
large amount of available carbohydrates resulting from high photosynthetic
activity in large trees (Cramer and Kozlowski, 1960) and variation in crown
vigour between trees in the same size class. The differences reported cannot be
attributed to environmental factors because the trees were growing within the
same stand, indicating a possible genetic influence.
The mature fruit is described as yellow, yellow-brown or brown in colour
and is 3.3 cm in diameter; it is round with a tough skin. Additional fruit colour
variations have been documented to include cream and brownish-red (rufous)
(Mwamba, 1995). The pulp is yellow and sweet with a pear-like taste and
contains three or four seeds. In some natural populations there are some slight
colour differences between individual trees: brownish-yellow and reddish
(Hans, 1981). The fruit dimensions fall within the 2-4 cm range in length and
breadth.
There are variations in fruit size, skin, pulp content and seed weight and
volume between and within populations and trees (Mwamba, 1995). At
maturity, each fruit may weigh 5-50 g. The amount of pulp ranges from 0.2 to
30 g but this varies among sites (Kwesiga et al ., 2000). Fruiting is biannual, i.e.
alternate fruiting seasons. Some trees produce a mixture of small and large
fruits while others habitually produce large or small fruits. The fruits may be
thick- or thin-skinned (Mwamba, 1989). This variation is due to local
competition between fruits for assimilates (Cramer and Kozlowski, 1960). At
maturity, a hard, thick exocarp encloses a thin, yellow mesocarp about 1.5 mm
thick when dry (Radcliffe-Smith, 1988). The skin accounts for approximately
38% of the total fruit weight (Mwamba, 1989). The fruit contains three to five
seeds (pyrenes), but three or four is the most common number; they are
generally whitish, cordate, carinate and apiculate with a tough fibrous
sclerotesta. The four-seeded fruits are larger, have thinner skins and contain the
most pulp (Mwamba, 1995). Seeds up to 2 cm long and 1.4 cm wide have
been recorded (FAO, 1983). The pulp accounts for 39-45% of the fruit weight.
Uapaca kirkiana is dispersed by animals; the sugary pulp is attractive to a
wide range of mammals and birds. In the natural environment, a large number
of birds, ungulates and primates feed on the pulp, dispersing the seed (after