Abstract:

The low natural fruit set rates of Calotropis gigantean L. decreased the ecnomic application in fibers. The surveies on the blooming progress，floral traits，flower-visiting insects，pollen viabilities，stigma receptivity，and breeding system of the wild C. gigantean groups in Yuanjiang region of Yunnan，were performed.（1）The C. gigantean flowers had sympodium umbels，the hyacinthine corollas，blooming all the year round and the flowering phase of 7–8 d. Their pollen had strong vitalities and stigma possessed certain receptivity during the flowering. The anther height was lower than the stigma height. All pollen grains which were wrapped by the ceraceous thin film and formed the pollinaria could not scatter and fall on the stigma. Consequnently，there was the spatial isolation between the anther and the stigma.（2）The hybridization indexes of 4 indicated that the breeding was the outcrossing and partly self-compatible，and demanded the pollinators. That the pollination on the anther slit instead of the stigma had certainlimitations was surveyed through the test of the hand-pollinate on the C. gigantean.（3）The test on the hand-pollinate on the C. gigantean revealed that the pollination on the Stigmatic chamber rather than the stigma resulted in the limitiations to pollination. There were no spontaneous self-pollination phenomenon and no apomixis phenomenon under field conditions. The setting ratios of the artificial pollination surveyed on the outcrossing were higher than which surveyed on the self-pollination. Therefore，the setting rate differences between them verified the results of the hybridization indexes.（4）The insect moved out the pollinaria and inserted it into the Stigmatic chamber to finish the pollination，using their special body parts. More than ten kinds of flower-visiting insects were surveyed on the C. gigantean and the pollinating insects mainly were the MicrMicrapis andreniformis Smith，Xylocopa tenuiscapa and a specie of the Xylocopa family. Pollen limitation is the main reason of the low C. gigantean fruit setting rates，and the fruit production of the C. gigantean can be improveded through the rearering of the main pollinators.

Key words: Calotropis gigantean, pollination biology, floral syndrome, breeding system, gynostegium, pollinia