Cross Breeding of Polyembryonic Varieties and Immature Embryo Rescue Culture in Citrus

摘要

In the present study, these poly-embryonic varieties including ' Kamei' (Citrus unshiu) , ' Jinshuigan' (C. reticulata) and ' Taoyecheng' (C. sinensis) were used as seed parents in five cross combinations. The male parents came from ' Taoyecheng ' (Citrus sinensis), ' Jinshuigan ' (C. reticulata) and 'Bingtangju' (C. reticulata). The pollen fertility was detected in the experiment. The results showed that the three male parents pollen were normal and their average germinating rate was 10.4% , 13. 5% and 9. 3% , respectively. Every anther contained 2.4×104, 3. 7×104 and 1. 9×104 pollen grains, and the pollen viability after staining was 84.0%, 87.0% and 77.1%. The data indicated that the three kinds of pollen had high viability and could be used as cross parent in future crossing. In the test, the highest fruit setting percentage was 15. 4% (' Jinshuigan' X ' Bingtangju'), secondly was 11.6% ('Kamei' X 'Taoyecheng'). All cross combinations obtained some hybrid fruits and seeds. Because polyembryony decreased citrus breeding efficiency, we had a study on culture of citrus immature embryos in vitro during 90 - 110 days after pollination to obtain zygotic off-springs. The zygotic embryonic seedlings were got by separating the multi-embryoies one by one in seeds of the five combinations. Furthermore, we selected the optimum period for young embryo culture in vitro. It was found that the optimum time for embryo rescue of ' Kamei' Satsuma (S)×'Jinshuigan' ponkan (P) was 105 days after pollination, and for embryo rescue of 'Jinshuigan' ponkan (P)×' Bingtangju' tangerine (B) and 'Taoyecheng' orange (T)×'Jinshuigan' ponkan (P), were both 95 days after pollination. Young embryos could survive on MT medium supplemented with 1.0 mg/L GA3, and the young seedlings could root after inoculated on 1/2 MT medium supplemented with 0. 5 mg/L NAA and 2% sucrose, and the rooting rate reached above 95%. By culture of young embryos in vitro, 533 plantlets were obtained from the five cross combinations. Survival of test-tube seedling transplanting was 72. 0% by seedling training in the closing bottle, and using the soil matrix containing humus, garden soil and sand mix by the ratio of 3∶3 ∶1, the plantlets could normally grow and survive after transplantation to the greenhouse.