Causes of low seed set in the natural tetraploid Trifolium pratense L. (Fabaceae)

Light and electron microscopic examinations were done at the cell level to research which factors would effect seed formation and the amount of effectiveness of natural tetraploid Trifolium pratense L. variety E2. In this investigation, origin of factors handicapping the seed formation and the results were determined by examining the development of ovule at six different phases to ovary size from the begining to formation of the seed. In this study, we observed that mature embryo sac was formed in 18% of ovules examined, but seed formation was obtained only in 5.8%. As the rate of seed set was lower than formation of the mature embryo sac, this investigation was done with the aim of determining the degeneration of the cells in the natural tetraploid T. pratense L. ovules.      Key words: Seed set, Trifolium pratense L., ultrastructure.