A Study On Reproductive Barriers And Early Embryo Rescue In Distant Hybridization Of Rosa. Laevigata

Seeds are seldom obtained in the distant hybridization between Rosa hybridas and Rosa laevigata Michx., which seriously influences utilization of excellent genes from Rosa laevigata Michx..With an aim to reveal the factors leading to infertility in the crosses between modern rose varieties (female parent) and Rosa laevigata Michx. (male parent), we carried out the artificial orientation hybridization between diploid wild species in rosa-Rosa laevigata Michx and four Rosa hybridas, which are’Luwangte’、’Gelin Jiaohong’、 ’Belle de Londres’、’Mount Shasta’、’Dongfang Yuxiao’ and ’Huoyanwu’, tested pollen viability of male parent, examined germination behavior of pollen grains on the stigmas after pollination, and observed embryo development. The main results and conclusions are listed as follows:(1) In the four crosses between’Dongfang Yuxiao’(female parent) Rosa laevigata Michx. (male parent) and four modern roses varieties, which are’Luwangte’、’Gelin Jiaohong’、’Belle de Londres’and’Mount Shasta’, It was found that before the four Rosa hybridas pollinating, the pollen viability of male parent was respectively 8.0%、22.0%、 63.7%、39.8%.No pollen grains ger- minated on the stigmas during 2h after pollination except for the stigmas of’Belle de Londres’with 8.1, and respectively 17.6、21.9、11.7、 12.0 pollen grains germinated on each stigma of the four varieties at 4h after pollination; At 12h after pollination, the number reached the highest value, which are 23.4、60.4、40.3、 34.4 respectively; Subsequently, the number was quickly decreased, most pollen tubes were thin、short and curved, stayed on the stigmas’ surface and failed to enter ovaries. In addition, during the different time after pollination, Average germinating rates on each stigma was increased first and then decreased. At lOd after pollination, many globular embryo in ovaries began to degenerate, torpedo and cotyledonary embryos can be observed in the two crosses between Rosa laevigata Michx. And the twoRosa hybridas, which are ’Belle de Londres’ and ’Mount Shasta’, but in the later phase, these embryos degenerated. These results suggest that the male pollen viability was not low, but 24h after pollination, most germinated pollen grains on the stigmas were abnormal before fertilization, and degeneration of a large number of embryos after fertilization, which may be the main factors resulting in infertility in the crosses.(2) In the two crosses between Rosa laevigata Michx. (female parent) and two rosa hybridas——’Dongfang Yuxiao’ and ’Huoyanwu’(male parents), It was found that before the two Rosa hybridas pollinating, the pollen viability of male parent was respectively 39.8%; During the different time after pollination, Average germinating pollen number and germinating rates on each stigma were increased first and then decreased, and at12h after pollination, the two numbers reached the highest value. Subsequently, most pollen tubes were thin、short and curved, stayed on the stigmas’surface and failed to enter ovaries. At 48h after pollination, there are few geminated pollen grains. At 10d after pollination, many eraly embryo in ovaries of Dongfang Yuxiao began to degenerate, and as a consequence, no seeds were obtained; Torpedo and cotyledonary embryos can be observed in ovaries of Huoyanwu, but in the later phase, these embryos degenerated, and seed set was only 7.2%. These results suggest that the male pollen viability was not low, most germinated pollen grains on the stigmas were abnormal before fertilization, and degeneration of a large number of early embryos after fertilization, which may be the main factors resulting in infertility in the cross between Dongfang Yuxiao and Rosa laevigata Michx., whereas only embryo abortion is a main factor resulting in low seed set in the cross between Huoyanwu and Rosa laevigata Michx..(3) Zygotic embryos were cultured in vitro to obtain hybrid plantlet with Rosa chinensis, Rosa hybrida ’Belle de Londres’, Rosa hybrida ’Mount Shasta’ and ’Huoyanwu’ as female parent and Rosa laevigata Michx. as male parent, results demonstrated that 32-40d was an optional stage for early embryo rescue. Plantlet germinating from embryo, whose female parent was Rosa hybrida’Mount Shasta’, could be proliferated on MS+6-BA1.0 mg/L+GA30.5 mg/L+NAA0.05 mg/L, while MS+6-BA0.1 mg/L+GA31.5 mg/L+NAA0.05 mg/L was suit for embryo whose female parent was Rosa hybrida’Belle de Londres’. To induce plantlet rootage, using NAA0.05 mg/L alone was better than combining it with 6-BA. Ground substance with ratio of perlite:vermiculite:turf=1:1:1 or 2:1:1 was idea to transplant.