THESIS

when the larger-flowered species were used as male parent, such a barrier would not
exist and hybrid seed was often obtained (Edmonds and Chweya, 1997).
However, the occurrence of polyploidy in the section Solanum is probably the
most efficient barrier to natural hybridization between these species. Successful
crosses are more difficult between taxa of different ploidy levels than they are
between taxa of the same chromosome number, with interploidy crosses leading to the
development of morphologic intermediate but sterile progeny. In contrast with report
of Edmonds (1977) who found that such interploidy crosses were not dependent on
the use of the higher ploidy level as the maternal parent. Nevertheless, species of
differing chromosome levels can be induced to cross and the chromosome number of
the resultant progeny can often be doubled experimentally, to restore the fertility of
such amphiploid plants (Edmond, 1979).
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