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Larva and pupa of Sibinia pellucens are described in detail. The larvae were collected from fruits of Melandrium album (Caryophyllaceae); some larvae were reared till pupation.
Placentae of Melandrium album excised from ovaries of unopened flowers were pollinated in vitro with pollen grains of Lychnis coronaria. Pollen grains germinated, and pollen tubes were found entering the micropyles 18 h after pollination. Double fertilization occurred. Immature and mature hybrid embryos at different stages of development were analyzed up to the third week of culture. Twenty-five days after culture, cotyledonary embryos were isolated from ovules and transferred to MS medium supplemented with 0.5, 1 or 2 mg l-1 indole-3-acetic acid (IAA). About 85% of the 115 inoculated embryos died shortly after transfer to medium, due to atrophy of the root and one cotyledon. Eighteen embryos survived; of these, 16 well-formed seedlings with root system were transferred to soil. The hybrid plants grew normally, and their hybridity was confirmed by morphological study. Female and male organs of the intergeneric hybrid were completely sterile.
In vitro placental pollination can be employed to overcome barriers of self-incompatibility and cross-incompatibility. Pollen grains of self-incompatible plants are capable of germinating directly on ovules, and the whole process of sexual reproduction can be accomplished. In some combinations of crosses, direct pollination of ovules enables prezygotic incompatibility barriers to be overcome. As a result, hybrid embryos or even hybrid plants can develop, depending on the partners crossed. Pollen grains germinate abundantly on immature ovules irrespective of the stage of megasporogenesis or megagametogenesis, and their tubes can penetrate the integuments and the nucellus cells. Preliminary investigations revealed that pollen grains of seven selected species of gymnosperms germinated on ovules of various species of Angiospermae. Embryological analysis of ovules of Melandrium album fixed 3 days after pollination with pollen of Pinus wallihiana revealed the presence of remnants of pollen tubes and 2-celled embryos in the embryo sacs. Those preliminary observations have not been described heretofore.
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