Towards a Domestication Strategy for Indigenous Fruit Trees in the Tropics - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 33

The use of juvenile tissues

Seedlings, coppice shoots and root suckers are the sources of juvenile tissues. For
tree domestication purposes, coppice shoots from the stumps of felled trees have
the advantage that it is possible to propagate trees that have already proven to be
superior, as it is possible to determine the phenotypic quality of the tree prior to
felling. This is highly beneficial in the domestication of trees producing all kinds of
agroforestry tree products, but has the added advantage in dioecious fruit tree
species that it allows cultivars to be restricted to trees. Nevertheless, there are
three reasons why the use of seedlings may still be preferred over coppicing from
trees of known phenotype (Leakey and Simons, 2000):

● The population of mature timber trees may be dysgenic because the elite

specimens may have been removed by loggers, which means that seedling
populations have a better array of genetic variation.

● The felling of large numbers of mature trees for the purpose of generating

cultivars may not be acceptable to the owners. In addition, felling the
mature trees may be environmentally damaging.

● The use of seedlings allows the screening of far larger populations, with

much more diverse origins, maintaining genetic diversity among the cultivars.

Whether using seedling or coppice stumps as stockplants, it is important to
ensure that they are managed for sustained, cost-effective and easy rooting.
The way in which stockplants are managed is probably one of the most
important determinants of the long-term success of a cloning programme.
Good rooting ability is maintained by encouraging vigorous orthotropic growth
of shoots from regularly pruned stockplants. This requires a much greater level
of knowledge than is available for most, if not all, tree species. Good progress
has been made in starting to unravel the sources of variation in rooting ability
(Leakey, 2004). For example, it has become clear that cuttings taken from
different parts of the same shoot differ in their capacity to form roots (Leakey,
1983; Leakey and Mohammed, 1985; Leakey and Coutts, 1989) and that this
is influenced by cutting length (or volume). In addition, there are influences on
rooting ability that originate from factors between different shoots on the same
plant (Leakey, 1983). These factors are also affected by shading, which
determines both the amount and the quality of light received by lower shoots.
Both the quality and the quantity of light independently affect the physiology,
morphology and rooting ability of cuttings from differently illuminated shoots
(Leakey and Storeton-West, 1992; Hoad and Leakey, 1996). To further
complicate this situation, the nutrient status of the stockplant interacts with the
effects of light and shading (Leakey, 1983; Leakey and Storeton-West, 1992),
with shading and a high level of nutrients combining to enhance rooting. Light,
especially light quality, also affects the relative size and dominance of different
shoots on managed stockplants (Hoad and Leakey, 1994). There are also
interactions between stockplant factors and the propagator environment.
The complexity of the stockplant factors affecting rooting ability means that
for the production of large numbers of cuttings from stockplants it is important
to develop a good understanding of these factors. This level of knowledge is