Effects of exogenous paclobutrazol and sampling time on the efficiency of in vitro embryo rescue in the breeding of new seedless grape varieties

Embryo rescue technology plays an important role in seedless grape breeding. However, the efficiency of embryo rescue, including the embryo formation, germination, and seedling rates, is closely related to the parental genotypes, degree of abortion, growth medium, and plant growth regulators. In this study, we investigated the effects of different concentrations of paclobutrazol (PAC), a plant growth regulator, and embryo collection times on the embryo formation, germination, and seedling rates for different hybrid combinations of grape breeding varieties used for their aroma and cold-resistance traits. The results showed that the different PAC concentrations had varying impacts on the development of ovules and embryos from the different grape varieties. The embryo formation rates of the 'Sultanina Rose'×'Beibinghong' and 'Kunxiang Seedless'×'Taishan-2' crosses were the highest under the 5.1 μmol L–1 PAC treatment. The 1.0 μmol L–1 PAC treatment was optimal for the germination and seedling development of the 'Sultanina Rose'×'Beibinghong' embryos, whereas the 0.2 μmol L–1 PAC treatment induced the highest germination rate for the 'Sultanina Rose'×'Kunxiang Seedless' cross. The optimal sampling times for each cross varied as 39 d after pollination (DAP) for the 'Flame Seedless'×'Muscat Hamburg' cross, 46 DAP for the 'Kunxiang Seedless'×'Beibinghong' cross, and 41 DAP for the 'Ruby Seedless'×'Beibinghong' and 'Fantasy Seedless'×'Shuangyou' crosses. Moreover, the medium modified with 0.5 g L–1 of indole-3-butyric acid allowed the malformed seedlings to develop into plantlets and achieve larger progenies. This study provides a useful basis for further studies into grape embryo rescue and could improve breeding efforts for new seedless grape varieties.