Pollen quality limits seed set in Burchardia umbellata (Colchicaceae)

In self-incompatible plants, interference by self pollen or genetically rel ated pollen can potentially exacerbate pollen limitation, although this has rarely been demonstrated. We examined the breeding system, pollen limitati on, and pollen interference using self- and cross- pollinations and pollen supplementations in Burchardia umbellata, an insect-pollinated lilioid mono cot. Ovule fertilization and seed set were less following selfing than cros sing (22 vs. 78% and 4 vs. 73%, respectively), indicating partial self-inco mpatibility. Flowers were partially protandrous, and flowers opened concurr ently on plants potentially allowing self pollen interference. Natural seed set was pollen limited and varied within and among years, probably due to variation in flowering plant density. Interference by self or genetically r elated pollen caused pollen limitation as evidenced by increased seed set o f bagged cross-pollinated plants compared to unbagged pollen-supplemented p lants in two years. In 1996, both fertilization and seed set increased in r esponse to cross-pollination, indicating that interference occurred in the style and ovary. In 1997, only seed set increased after cross-pollination i ndicating that interference occurred in the ovary. Inappropriate pollen dep osition may contribute to pollen limitation more often than previously reco gnized and should select for floral traits that decrease deposition of self or related pollen.