Schriften zu Genetischen Ressourcen - Genres

R.N. LESTER and M.-C. DAUNAY
very different in morphology from their wild ancestors, but also that these cultigens
display a vast range of diversity within themselves. On the other hand, wherever
studies of molecular markers such as isozymes and DNA have been made, the diversity
within the cultigens has been found to be little or no greater than that of the
wild ancestor. This situation, which is shown diagrammatically in Figure 1, is also
exemplified clearly by tomato (Lycopersicon esculentum), pepper (Capsicum annuum),
and especially by maize (Zea mays) (DOEBLEY et al. 1987, LESTER 1989,
LEFEBVRE et al. 2001). This seems to be a general rule for all domesticated species
of plants (except perhaps those derived from interspecific hybridisation). This paradox,
of the vast and deviant morphological diversity of cultigens compared to their
wild ancestors on the one hand, and the minimal increase in diversity of molecular
markers such as DNA and isozymes on the other, demands an explanation.
To begin with, let us consider some of the morphological changes that have occurred
during the domestication of Solanum aethiopicum. LESTER (1989) stated that “In Solanum
anguivi, the wild ancestor of the scarlet eggplant, development of flowers and
subsequent fruits is rapid and apparently under close genetic control: the ovary is
composed of precisely two locules, and after pollination it enlarges to exactly 1 cm
diameter and then stops. The colour changes rapidly from green to red, the flesh
Fig. 1: Diagram showing that in morphology a domesticated species is different
from its wild ancestor and displays much greater diversity,
whereas in isozymes, DNA or other molecular markers the diversity
remains much the same
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