However, the molecular mechanism of the
pollen–pistil incongruity of Cucumis spp. has not been revealed.
It is therefore difficult to discuss possible scenarios to explain
the effects of temperature. In contrast to results obtained for
the interspecific crosses, the temperatures of 24–34 ◦C did not
affect pollen tube growth in the self-pollination of four Cucumis
spp. (Fig. 5). The pollen tubes in self-pollination grow still faster
than the pollen tubes promoted by higher-temperature conditions in interspecific crosses (Figs. 3 and 5). These results suggest
a temperature-sensitive cause of the pollen–pistil incongruity:
higher-temperature conditions can partially recover the pollentube
growth from the incongruity.