Origin of Tetraploid Progenies in 4x×2x Crosses of Cyclamen (Cyclamen persicum Mill.)

Abstract

The origin of tetraploids from 4x × 2x cyclamen crosses was examined by using the diploid pollen parents with and without giant pollen grains, and by pollinating tetraploid cultivars with sieved giant and normal-sized pollen grains borne on diploid plants. The developing pollen mother cells were observed after the second meiotic division in the diploids with and without the giant pollen grains. Tetraploid progeny production in the crosses was obviously related to the giant pollen grains. Tetraploid F₁ progenies were produced in the crosses by using pollen from diploid plants that produce giant pollen ; no seed was obtained in the crosses by using pollen from diploids, which produce no giant pollen. More seeds were obtained when sieved giant pollen grains were used for the crosses than when non-sieved pollen grains with giant pollen were used, whereas no seed was obtained in the crosses using only normal-size pollen grains from diploids. Thirteen to 27% of pollen mother cells in the diploids with giant pollen grains formed pollen dyads or triads after the second meiotic division, whereas few pollen dyads and triads were formed in those without giant pollen grains. These observations suggest that most giant pollen grains in diploid cyclamen are unreduced male gametes. Therefore, the origin of tetraploids derived from 4x × 2x cyclamen crosses is the results of fertilization between an unreduced pollen grain from the diploid plant and a normally reduced egg cell from the tetraploid. Furthermore, the use of sieved giant pollen grains was efficient for the production of tetraploid progenies.