Intra- and interspecific reproductive barriers in Crocus (Iridaceae)

The reproductive system was studied in Crocus genus (Iridaceae) following intra- and interspecific pollination, by using light and scanning electron microscopy. The results suggest that the stigma-style tract of the Crocus pistil is a mere promoter of pollen tube growth, while intra- and interspecific discrimination of compatible and incompatible pollen occurs in the ovarian tract. Here, the transmitting tissue consists of special epidermal cells, whose granular or floccular secretions provide the selective medium for the growth of pollen tubes. The ovarian self-incompatibility (SI) is widespread within the genus, resulting in a partial or complete suppression of self-fertilization. Moreover, postzygotic SI mechanisms, as well as postzygotic mechanisms of unknown nature, seem to be recurrent and both are responsible for seed abortion. The interspecific ovarian incompatibility concerns only unrelated crosses; crosses between related fertile species succeed both in fertilization and seed-set.