THESIS

48) was crossed with diploid S. nigrum (2n = 24). This finding is in contrast to result
obtained by Edmonds (1977) who found that both S. villosum and S. nigrum crosses
within and also between species (recognized in each taxon in morphologically
intermediate) gave extremely vigorous and fertile F1 progeny.
When S. nigrum was used as female parent, only one accession of S.
americanum (S00861) could be crossed with S. nigrum (TS02930) and 39.8 % (Table
18) fruit setting with both viable and abortive seeds were obtained. When S. nigrum
was used as male parent slightly lower fruit setting was obtained. Similarly, only one
accession of S. villosum could cross with S. nigrum. The crossing of S. nigrum
(TS02930) x S. villosum (S00860) gave 22.0 % of fruit setting and obtained hybid
seeds but no hybrid plant is obtained.
These results showed that the unsuccessful crosses may be due to the
hybridizations involving accessions from distinct geographical origins of S. villosum,
S00854 (collected in Tanzania) and TS02600 (collected in Kenya) both Africa and
TS02930 (S. nigrum) from Malaysia. Contrasting with S00860 (S. villosum collected
in Japan) was successfull crossed with TS02930 (S. nigrum). This present finding was
in agreement with the report of Ganapathi (1988) who obtained a heptaploid hybrid
(2n = 7x = 84) by crossing S. nigrum (2n = 6x = 72) with pollen of S. villosum (2n =
4x = 48). Moreover, Khan et al. (1978) who found that cytogy of hybrids of the cross
tetraploid S. nigrum x S. americanum and their amphidiploids obtained through
colchicine treatment revealed that the structural difference between chromosomes of
parents plays an important role in diversification of morphological characters of the
two taxa and the tetraploid S. nigrum and S. americanum play an important role in
origin and evolution of natural hexaploid S. nigrum.
Moreover, interspecific hybridization are considerably more successful when
species of the same floral size are involved. Crossing using the smaller-flowered
species paternally (male parent) and large-flowered species maternally (female
parent) are 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,
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