Abstract: Nanfeng tangerine[Citrus reticulata Blanco var. Kinokuni（Tanaka）H. H. Hu] was used for studying its seedless forming causes based on the observation of pollen fertility，embryo sac development，and embryonic development. The results showed that the pollen fertility of Nanfeng tangerine belongs to the medium fertility pattern. The mature embryo sac of the Nanfeng tangerine was normal. Most of zygotic embryo stopped growing and began to abortion at 4 weeks after pollination. Some plump seed endosperm began to collapse when the embryo developped into heart-shaped embryo at 8 weeks after pollination，and formed empty-seed and degenerated seeds with funiculi could be observed until 16 weeks after pollination. Another plump seeds developed into normal seeds or plump seeds which filled with endosperm but abnormal embryo. All seeds of Xiaoguo Nanfeng and Zaoshu Nanfeng and most seeds of Daguo Nanfeng were degradated in mature fruit. It is hence proved that embryo degeneration is responsible for the seedless of Nanfeng tangerine.

Key words: citrus, Nanfeng tangerine, pollen fertility, embryo sac development, embryonic development