Towards a Domestication Strategy for Indigenous Fruit Trees in the Tropics - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 39

It is clear from the above discussion that in the early phases of domestication
there is sufficient genetic variation in most tropical tree populations to allow
considerable progress in the development of cultivars, but a strategy for clonal
agroforestry should not forgo any opportunity for creating new variation.
The selection of clones is not a once-and-for-all event. Domestication is a
continuous process, which in wheat, rice, maize, oranges and apples, for
example, started thousands of years ago and continues today. Thus, a series of
clonal selection trials should be established to seek the best individuals from
new accessions of genetically diverse populations or progenies (Fig. 2.2). It is
also important to discard old clones as they are superseded, although some of
these should be retained in the gene resource population. In the first instance,
clones may be selected for yield and quality. With time, this can be extended to
include nutritional quality, disease/pest resistance, component products (oils,
flavourings, thickening agents, etc.). This continued turnover of the selected
clonal population will further ensure the diversity of the commercially planted
clones and prevent excessive narrowing of the genetic base. Indeed, it can be
argued that in this way clonal plantations of 30-50 superior but unrelated
clones can be more diverse than seedlings. This is because seed-lots typically
originate from a number of related mother trees and share some genetic
material.
Because domestication is a continuous process, commercial plantings have
to be made with whatever material is best at a given time, knowing that they
will be superseded later. Having a succession of increasingly good planting
stock is one of the ways in which the diversity of the genetic base can be
maintained, although of course this has to be rigorously enforced as one of the
objectives of a breeding and selection programme. For species with existing
provenance selection and breeding programmes, clones should be derived
from seed collections sampling a wide range of the known variation, as it is not
uncommon for a few elite trees to be found with poor provenances.
As the selection process intensifies with time, new traits will be introduced
into the programme (e.g. seasonality of production, early fruiting, disease
and/or pest resistance and drought tolerance). Capturing variation in the
seasonality of production and expanding the harvesting season are likely to be
among the best ways of supporting market growth. As the price of end-of-
season fruits is likely to be better than the mid-season price, it is also a good
way to enhance the benefits of producing households that need sources of
income throughout the year. The further the domestication process proceeds,
the more important it becomes that the combination of traits being selected is
targeted at a particular market (Fig. 2.4). This again is where the ideotype
concept can be useful, and ideally advice should be sought from industrial
partners who are aware of which characteristics are important in the
marketplace or in product processing (Leakey, 1999).
Using the example of Sclerocarya birrea , fruit-producing cultivars could be
developed that have large fruit flesh/juice mass (Leakey et al ., 2005a) and are
nutritious (Thiong'o et al ., 2002) as raw fruits, or are good for traditional beer-
or wine-making, or meet the needs of the distilling industry. Likewise, other
cultivars could be developed for the size and quality of the kernel, with a low