the fruits contained no mature seeds
(Table 2). The globular stage embryo observed in the cross between
C. anguria and ‘MR-1’ shows that the fruits were not parthenocarpic
(Fig. 6b); hybrid embryo abortion occurred from 15 days to 45 days
after pollination. These results demonstrate that pre-fertilization
barriers can be overcome by higher temperature conditions in
these three cross combinations. However, because our preliminary
attempts to obtain a hybrid by ovule culture were not successful,
the development of some means to overcome post-zygotic reproductive
barriers is a problem that remains to be solved for obtaining
hybrids.