Germplasm Supply, Propagation and Nursery Management of Miombo Fruit Trees - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 350

deactivated with time or by certain seed treatments. Delayed and irregular
germination is therefore a serious constraint in the large-scale propagation of
miombo fruit trees. Quickly germinated seeds may have a greater chance of
producing seedlings than seeds that take longer to germinate, which may be
exposed to an increased likelihood of fungal, insect or rodent attack. In practical
terms, delayed germination will also tie up nursery beds for prolonged periods,
increasing nursery costs and reducing seedling vigour (Prins and Maghembe,
1994). It may also increase variability in growth after establishment. Hence,
special seed pretreatment is required to induce quick and uniform germination.
Various seed pretreatments have been studied for some of the miombo
fruit trees, and selected recommended practices are presented in Table 19.1.
Various methods, including seed cleaning, soaking in cold or hot water,
mechanical scarification and acid scarification, are often recommended to
overcome dormancy.
In the case of Flacourtia indica , small seeds have either no embryo or have
a very hard seed coat, which makes imbibition difficult (Prins and Maghembe,
1994). Nicking and removal of the seed coat should have a marked positive
effect on germination. However, the small size of the seed and the hard seed
coat often results in embryo damage during pretreatment, resulting in poor
germination when seeds are nicked or the seed coat is removed, probably
because of unimpeded swelling resulting in internal damage. The difficulty with
Parinari curatellifolia is that seeds deteriorate quickly at high temperatures. The
endocarp is also very hard, making it difficult to extract the seed without
damage (Prins and Maghembe, 1994), and often the seed is no longer viable
before sowing. To make up for this, nature has made the roots of Parinari
curatellifolia sproutable.
Seeds of Sclerocarya birrea do not germinate well without seed pretreatment.
Hall et al. (2002) summarize studies conducted by various workers on seed
pretreatment and the germination of Sclerocarya birrea (Table 19.1). Teichman et
al . (1986) investigated the influence of several factors on the germination of
Sclerocarya birrea , including scarification with concentrated sulphuric acid and
soaking in potassium hydroxide for 24 h, and the effects of temperature and the
exposure of intact and de-operculated endocarps to white light. Scarification with
sulphuric acid was ineffective. Germination was higher at temperatures ranging
between 27 and 32°C. White light was concluded to have an inhibitory effect on
germination. Removal of the operculum led to a pronounced increase in
germination, while soaking in potassium hydroxide solution and leaching with
cold water further increased germination (Teichman et al. , 1986). The endocarp
was suspected to protect the seed from leaching, which might remove
germination-inhibiting substances (Hall et al. , 2002). The germination rate of
seeds from endocarp soaked in cold and hot water has also been shown to be
higher than that of those with untreated endocarps (Msanga, 1998; Mateke and
Tshikae, 2002). Many workers have also investigated prolonged seed storage as a
way to increase germination success (Hall et al. , 2002). According to Teichman et
al . (1986), de-operculated endocarps of S. birrea subsp. caffra stored for 14-23
months had a germination rate of over 80% in 6 days compared with <50% for
endocarps stored for 2 weeks to 2 months. In Botswana, removal of the