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Diversity of African vegetable Solanum Species
striped), white or purplish at first, ripening to a scarlet, fleshy, sweet fruit, firmly attached
to the pedicel even when fully ripe (LESTER et al. 1986). Despite this great
morphological diversity, isozyme analyses showed relatively little diversity (LESTER
and THITAI 1989) and even less was found in the chloroplast DNA (SAKATA et al.
1991).
The inheritance of some morphological characters was studied by making F1 hybrids
between primitive S. anguivi or S. distichum and highly domesticated S. aethiopicum
Gilo, Kumba and Shum Groups, and then analysing the F2 generations (LESTER and
THITAI 1989). In general the F1 plants showed greater similarity to the primitive parent
in many more characters than to the highly domesticated parent. In some cases the
F2 showed simple dominance of the wild-type character state, such as for presence
of leaf prickles or presence of star hairs, whereas density of star hairs showed incomplete
dominance. However, other characters appeared to show dominance in the
F1, but the F2 proved that the inheritance was more complicated, such as for petiole
anthocyanin colouration, inflorescence length and flower number. This probably also
applied to several fruit characters, but unfortunately it was impossible to analyse the
F2 for these characters. For some other characters, such as sepal number, the F1
appeared to be intermediate, but the F2 showed a skewed distribution towards the
wild type, and leaf prickle number even showed transgression. Most of the F1 hybrids
showed heterosis or overdominance in plant height. The tendency to a greater similarity
to the wild parent has also been observed in hybrids between S. melongena
and many different wild species (DAUNAY, unpublished). However, hybrids between
different domesticates have sometimes produced unexpected characters. A cross
between S. aethiopicum Kumba Group and S. macrocarpon, both of which lack
prickles or hairs, produced a prickly though not hairy F1 hybrid. Some F2 progeny
from S. melongena crossed with S. macrocarpon were very prickly although neither
parent was. Furthermore, a cross between cultivars of S. melongena and S.
aethiopicum Gilo Group, each with few-flowered inflorescences, produced hybrids
with long multi-flowered inflorescences, as in both the wild ancestors (DAUNAY and
LESTER, unpublished). These cases illustrate atavisms, as observed long ago by
Darwin and others, and might be explained by complementation of different recessive
genes (DARWIN 1868, LESTER 1989).
Loss of gene function: a new paradigm for the domestication process
Considerations of the diversity of African vegetable Solanum species, and how they
have evolved from their wild ancestors, have led to conclusions that have implications
not only for eggplants, but for all domesticated plants (LESTER 1989).
For both scarlet and brinjal eggplants (S. aethiopicum and S. melongena) it has been
shown above that the domestication process has not only produced cultigens that are
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