| Citrus,the tropical and subtropical fruit tree which belongs to the Rutaceae.In Citrus breeding,polyploid breeding has attracted more and more attention,seedless Citrus is one of the most important breeding target.However,the best way to get the triploid is hybridization between diploid and tetraploid.Allotetraploid has a wider genetic basis than autotetraploid and been used as resistant rootstock and cross parent for breeding triploidy cultivars.Therefore,in this study,we took the hybrid of Citrus grandis‘ Shatianyou’×Citrus ichangensis(allotetraploid CSY and allodiploid SY)and their parents as experimental materials to study the fertility and creating new germplasm resources and provided important resources for Citrus breeding.The main results are summarised as follows.Compared with their parents,the pollen viability and the amount of pollen of the hybrid of Citrus grandis‘Shatianyou’×Citrus ichangensis was lower,and SY was lower than CSY.The hybrid pollen can germinate on the stigma.They can form uninucleate embryo sac and binucleate embryo sac,even six nuclear embryo sac.There is fertility of the hybrid of Citrus grandis‘Shatianyou’×Citrus ichangensis,but fertility is low compared with their parents.Compared with allodiploid,the fertility of allotetraploid was partial restored.PMCs meiosis of Citrus grandis‘Shatianyou’ and Citrus ichangensis were normal.However,PMCs meiosis of the hybrid of Citrus grandis‘Shatianyou’×Citrus ichangensis was abnormal.Abnormal PMCs of SY frequency was 21.93%,the univalent and trivalent were observed in metaphase,configuration is 1.45 I +7.45 II +0.55 III.The laggard chromosomes and unequal separating of chromosomes were observed in anaphase and telophase.Abnormal PMCs of CSY frequency was 30.40%,there were many multivalent in metaphase which frequency was 40.38%.The laggard chromosomes,unequal separating of chromosomes,bridge of chromosomes and micronucleus were observed in anaphase and telophase.GISH result revealed that the number of chromosomes of Citrus ichangensis divided into sub cells is different.This phenomenon may be one of the causes of pollen abortion and seed abortion.The traits of seed of the hybrid of Citrus grandis‘Shatianyou’×Citrus ichangensis combined the traits of parents.The testa was prismatic and reticulate,it’s color was yellow,single embryo,cotyledon was white and the shape was oval.There were many seeds in one fruit,and the seeds appeared abortion phenomenon.The normal seed number of CSY was 51,abortive seed number was 33,the normal seed number of SY was only 9,abortive seed number was 79.The results showed that the fertility of allotetraploid was partially restored after chromosome doubling.Compared with their parents,the fruit of the hybrid of Citrus grandis‘Shatianyou’ × Citrus ichangensis was bigger,the flavor was good.And edible rate,juice rate and soluble solids content was higher,but the peel was thick,it had a bad taste because of its high acid content and no fresh.So the hybrid can be considered to be as hybrid parents and create new germplasm resources.At the same time because of its high acid content,it may be considered as a natural flavoring agent and additives.The hybrid of Citrus grandis‘Shatianyou’×Citrus ichangensis as parents,we gained eight pollination hybrid progenies,including SY×Citrus grandis‘Shatianyou’,CSY×Citrus grandis‘Shatianyou’,Citrus grandis‘Shatianyou’×SY,Citrus grandis‘Shatianyou’×CSY,SY artificial ?,CSY artificial ?,CSY natural ?,CSY×Valencia Orange.We also created the germplasm resources of various ploidy hybrids between the hybrid of Citrus grandis‘Shatianyou’×Citrus ichangensis and Citrus grandis‘Shatianyou’ and provided new materials for Citrus genetic and breeding research.GISH analysis was used to study the origin of chromosomes composition preliminarily. |
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