Agriculture Reference
In-Depth Information
sucking the pulp) as they move from the seed source (Pardy, 1951; Storrs, 1951;
FAO, 1983; Dowsett-Lemaire, 1988; Seyani, 1991). The seed is white, with a
rather brittle seed coat. One side is almost flat and on the opposite side there is a
longitudinal ridge terminating in a sharp edge at the base. The seed has an inner
membrane, endosperm and two leafy green cotyledons. There are 2500 seeds
per kilogram. The seed has a high moisture content of about 48%, based on
sun-dried and fresh weights (Hans, 1981). The seed has no dormancy period
and once dispersed, it germinates readily. Fruit maturation and fall coincide with
the rainy season, ensuring the immediate availability of appropriate germination
conditions. In Zambia, up to 2039 and 1183 new and old seedlings per hectare,
respectively, were recorded in a natural population (Mwamba, 1992). Seedling
growth is better in the open than in the closed canopy.
Germination is intermediate between epigeal and hypogeal. The seed coat
cracks and the radicle protrudes from the scar end and develops into a tap
root. The seed coat splits longitudinally into equal halves and the two
cotyledons unfold and expand greatly. Germination is fairly uniform, reaching
30% after 4 weeks and 90% after 6 weeks. The seed does not require
pretreatment, but soaking in cold tap water overnight hastens germination
(Ngulube, 1996). Up to 100% germination has been achieved at Makoka
nursery (ICRAF, unpublished results).
Propagation
Until recently, vegetative propagation techniques have been a constraint to the
domestication of indigenous fruit trees. Jaenicke
et al
. (2001) reported a graft
take of less than 10% for
U. kirkiana.
However, these problems have been
overcome and grafting success rates are now relatively high (80%) (Mhango and
Akinnifesi, 2002; Akinnifesi
et al
., 2004).
U. kirkiana
is amenable to clonal
propagation and field management. Clonal propagation was used to capture
superior
U. kirkian
a clones in Malawi using a participatory approach (Akinnifesi
et al
., Chapter 8, this volume). Tree orchards of superior trees established at
Makoka, Malawi, started to bear fruits after 2 years and fruiting became stable
after 4 years, with a fruit load as high as 460 in some clones. Rootstocks are
propagated from seeds (seedling rootstocks). A medium made of 75% forest soil
and 25% sawdust has been shown to produce better soil media for rootstocks. A
graft take of 80% for
U. kirkiana
using a wedge or splice technique can be
obtained (Mhango and Akinnifesi, 2002; Akinnifesi
et al
., 2004). The time of
grafting and the skill of the grafter have overriding effects on the grafting success
of
Uapaca
. Scions collected and grafted between October and December are
best (>80% take), whereas grafting done between January and August has
resulted in less than 30% graft take (Akinnifesi
et al
., 2004, 2006). The method
used to store the scion is a major factor that can affect the lifespan. Research in
Malawi showed that keeping scions at room temperature was superior to other
storage methods (sand, wet paper, cooler box). Air-layering has the potential for
propagating plants with high vigour, and up to 63% rooting of marcotts has
been achieved in the wild (Mhango and Akinnifesi, 2002). However, it is still a
challenge to achieve good survival of established marcotts. The survival of the
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