Towards a Domestication Strategy for Indigenous Fruit Trees in the Tropics - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 42

2.5.2 The wise utilization of genetic resources in cultivation
( circa situ conservation)

A wise genetic resource strategy will ensure that the production population is
based on a diverse set of cultivars, and that this set of cultivars is continually
being supplemented with new and better cultivars from the ongoing screening
of wild populations, provenances, progenies, a programme of intensive tree
breeding, and the regular replacement of cultivars that are no longer the best.
In this way selected, highly productive but unrelated clones can be used
commercially for agroforestry. Indeed, ten well-selected and unrelated clones
may contain as much, or more, genetic variation as a narrowly based sexually
reproducing population.
This strategy will also ensure that the cultivars being planted are well
adapted to their environment - and thus fully expressing their genetic potential
- while at the same time minimizing the risks associated with intensive
cultivation. These risks are perhaps greater when indigenous trees, rather than
exotics, are planted in the tropics in areas where the complexity of forest
ecosystems has been disturbed; for example, by shifting agriculture. The
minimization of risk therefore requires that the trees are planted in situations
that ensure a minimum of damage to the nutrient and hydrological cycles, food
webs and life cycles of the intact ecosystem.
In clonal tree domestication programmes, final yield is strongly influenced
by the adaptation of the trees, individually and collectively, to the site. This
adaptation has two components: clonal development, and clonal deployment
or the stand establishment process (Foster and Bertolucci, 1994). Clonal
development approaches, including breeding, testing and selection, largely
affect the genetic quality of the resulting clonal population available for
planting. Clones must be developed which are highly selected for growth and
productivity traits, but which display substantial homeostasis and so can adapt
to their changing environment. Clonal deployment, on the other hand, must
strike a balance between the need for efficiency of management for the
economic production of products, and the need to deploy populations which
are genetically buffered against environmental changes, including pests.
Clonal development relies on three processes: breeding, testing and
selection. However, despite its overwhelming importance, little research has
been conducted to investigate the effects of different deployment strategies on
the health, growth and yield of forest stands. This type of research requires a
large amount of resources and a long period of assessment. Foster and
Bertolucci (1994) identified the following major questions:
● How many clones should be in the production population, and how many

should be deployed to a single site?

● Should the clones be deployed at a single site as a mixture or as mosaics of

monoclonal stands? This is important both for operational reasons such as
planting, and to maximize yield through the optimization of inter- or
intraclonal competition.

● What are the key attributes of the clones themselves that cause them to be

used either as mixtures or in monoclonal plots?