THESIS

herbicide (atrazine) resistant trait from S. nigrum is indicated by Southern analysis
(Guri and Sink, 1988b).
In addition, some of the mature hybrid fruits are parthenocarpic (Figure 8),
Most of them were found in the crosses between S. melongena x S. torvum, S.
melongena x S. americanum, S. melongena x S. villosum and S. melongena x S.
nigrum. The interspecific crossing among S. melongena and other four species (S.
torvum, S. americanum, S. villosum and S. nigrum), could be produced but some
hybrids seeds are abortive (Figure 9), and no hybrid seeds are obtained.
However, interspecific hybridization are considerably more successful when
species of the same floral size were involved, crossing using the smaller-flowered
species male parent and large-flowered species female parent were generally
unsuccessful, presumably due to the inablility of the pollen tubes from the small
flower to traverse the long styles of the female parent. Reciprocally, when the largerflowered
species were used as the paternal parent, such a barrier would not exist and
hybrid seeds were often obtained (Edmonds and Chweya, 1997).
Moreover, in interspecific hybrids, lack of coordination may cause unbalanced
production of growth regulating substances by the endosperm and hence abortion of
the embryo, or even unregulated production of nucleases and proteases resulting
firstly in autolysis of the endosperm and then digestion of the embryo. The endosperm
may thus serve to setect inappropiate hybridization of species or ploidy levels and so
prevent waste of resources by producing seeds that would result in sterile hybrids or
unthrify subsequent generation (Lester and Kang, 1998).
In addition, the success of gene introgression via sexual hybridization depends
on the phylogenetic relationships between species, opportunities for genetic
recombination and stability of the introgressed gene. Cytological analyses are usually
performed to evaluate the meiotic process in experimental hybrids (Hermsen, 1994).
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