Towards a Domestication Strategy for Indigenous Fruit Trees in the Tropics - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 40

shell : kernel ratio and with either nutritious or medicinal qualities for eating, or
with oil yield and quality traits of importance in the cosmetics industry (Leakey,
2005; Leakey et al ., 2005b). Similarly, superior phenotypes of U. kirkiana with
heavy fruit loads, large fruits and high pulp content have been identified by
communities during participatory selection in Malawi, Zambia and Zimbabwe
(Akinnifesi et al ., 2006). Thus, it is clear that in the domestication of
multipurpose tree species, highly productive, single-purpose clones or cultivars
are probably the best option. To maximize the market recognition of, and
farmer interest in, cultivars, it is a good idea to name them. In Namibia every
marula tree already has a name, so it is easy to give a name to a cultivar
derived from any particular tree. The name can also be used to recognize the
person or community holding the rights to the cultivar.
2.4 Opportunities for Introducing New Variation
A clonal selection programme seeks to utilize as much of the existing variation
as possible within wild populations, or within progenies from breeding
programmes. However, after the initial phases of selection, the opportunity will
arise for controlled pollinations between proven elite clones. In this way it may
be possible to take advantage of specific combining ability in unrelated superior
clones and to produce progeny with heterosis in desirable traits that exceed
what is found in the wild populations. The vegetative propagation of new
genotypes can become a second clonal generation. The philosophy of adding
new variation in clonal populations in the future can also be extended to the
possibility of using genetically manipulated materials arising from
biotechnology programmes.
Ideally, to make rapid progress in a second-generation breeding
programme, means of inducing early flowering in superior clones are needed in
order to shorten the generation time (e.g. Longman et al ., 1990).
2.5 The Wise Use of Genetic Variability
The genetic resource of a species is the foundation of its future as a wild plant
and as a source of products for human use. It is therefore crucial to protect and
use this resource wisely. Within the domestication process, whether clonal or
not, one of the first requirements of an appropriate strategy is to conserve a
substantial proportion of the genetic variability for future use in selection
programmes and, subsequently, through breeding to broaden the genetic base
of the cultivars in the production population. This also serves as a risk-aversion
strategy should it be necessary to breed for resistance to pests and diseases in
the future. There are three actions which each contribute to genetic
conservation: establishing a gene bank; the wise utilization of the genetic
resource in cultivation; and protecting some wild populations. These will be
discussed in the following sections.