Study on reproductive barriers in 4x–2x crosses in Dianthus caryophyllus L

Abstract

Reproductive barriers often exist in 4x–2x crosses in Dianthus caryophyllus L. and seriously lead to low seed set and breeding efficiency. In this study, we inspected pre-fertilization and post-fertilization barriers in crosses between ‘butterfly’ (2n = 4x = 60) and the fertile breeding line ‘NH10’ (2n = 2x = 30) and ‘NH14’ (2n = 2x = 30) using fluorescence microscopy and paraffin section. The growth of the pollen tubes up to the ovary was observed in crosses of ‘butterfly’ × ‘NH10’ and ‘butterfly’ × ‘NH14’. However, abnormalities of pollen tube including coiled and spiky and callose deposition in incompatible tubes has also been detected. In the cross ‘butterfly’ and ‘NH10’, the number of pollen tubes at the base of the style reached the highest value, 67.2 ± 10.8 at 48 h after pollination, but the number of ovules with micropylar penetration was low, 19 ± 4.5. Similarly, in the cross between ‘butterfly’ and ‘NH14’, pollen tubes at the base of the style at 48 h after pollination was 51 ± 6.2 and the ovules with penetrated micropyles per ovary at 48 h after pollination was 11 ± 2.4. It indicated the pollen tubes difficultly penetrated into the ovules in 4x–2x crosses. In addition, it was observed that non-fused of egg and sperm or non-fused polar nucleus resulted in endosperm without embryos, and embryos without endosperm. Embryos aborted at different developmental stages (prembryo to cotyledon embryo, main globular embryo), which might be related to a deficient endosperm development in reciprocal crosses. The results suggested that pre-fertilization and post-fertilization barriers were detected in these combinations. Due to the post-fertilization barriers in 4x–2x crosses, the embryo rescue might be contributed to obtain hybrid F1 plants.