Germplasm Supply, Propagation and Nursery Management of Miombo Fruit Trees - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 349

Uapaca kirkiana , complete removal of the seed coat gave 70-100% germination
(Hans, 1981; Maghembe, 1995; Mwabumba and Sitaubi, 1995), although simply
cleaning followed by soaking in cold water for 24 h yielded a similar results, i.e.
90-100% (Maghembe, 1995; J. Mhango, personal communication). This was
due to the presence of water-soluble germination inhibitors in the endocarp (A.S.
Hans, unpublished results). The endocarp extract has been shown to be acidic
(pH 3.7-5.8), which encourages fungal attack of germinating seeds when the
seeds are within the endocarp.
Germination can fail for abiotic or biotic reasons. An investigation of failure
of germination may reveal that the seeds have no embryos, the seeds are dead
because of ageing or treatment, or the seeds are in dormancy - all abiotic
factors. For seeds of some species, the inability to germinate is due to the
impenetrability of the hard seed coat by water (Werker, 1980). Azanza
garckeana , Canthium foetidum , Diospyros mespiliformis and Bridelia cathartica
have hard seed coats, which prevents easy seed germination. In other species,
such as Sclerocarya birrea and Parinari curatellifolia , the seed is embedded in a
hard stone-like structure (Mojeremane and Tshwenyane, 2004) that prevents
the seed from imbibing water and eventual germination. However, treatment of
Sclerocarya birrea seeds by manual nicking has resulted in 75% germination
(T. Chilanga, personal communication). If the operculum has not been opened
the seed may take up to 9 months or more to germinate depending on the
moisture status of the site and the rate of stone breakdown (Mojeremane and
Tshwenyane, 2004). If a seed is not exposed to sufficient moisture, the proper
temperature, oxygen and, for some species, light, the seed will not germinate.
In Zambia, Mkonda et al. (2004) showed that Strychnos cocculoides needs
no treatment as different scarification techniques yielded no improvement.
However, germination rates seem to be optimum 1-2 months after sowing, and
the rate can vary between provenances from 58 to 83% (Mkonda et al. , 2004).
Swai et al. (2004) obtained 91% germination for S. cocculoides in Tanzania
after thorough cleaning and soaking in cold water for 24 h.
Some miombo woodland fruit species still have germination problems. For
instance, Mwabumba and Sitaubi (1995) obtained no germination for
Flacourtia indica and Parinari curatellifolia in Malawi. Vitex doniana had a low
germination rate regardless of different treatments (Mwabumba and Sitaubi,
1995), but Vitex doniana gave 69% in Tanzania (Swai et al. , 1995). There were
low germination rates for Flacourtia indica (0-16%), Parinari curatellifolia
(0-23%) and Boehemia discolor (0-9%) regardless of treatment (Swai et al. ,
2004). Maghembe (1995) obtained only 20% germination for Parinari
curatellifolia and 17% for Flacourtia indica when seeds were sown directly after
removing the pulp but without treatment.
Viable seeds are considered dormant when they fail to germinate under
normal conditions suitable for germination. The expression of dormancy is
under genetic control, but it is also strongly influenced by environmental factors
(Osborne, 1981; Naylor, 1983). Seed dormancy is nature's way of setting a
clock that allows seeds to initiate germination when conditions are favourable
for germination and to ensure survival of the seedlings. Seeds from indigenous
fruits may also contain germination inhibitors that may be removed or