Study On Chromosomal Homology Of Polyploid Chinese Cherry(Cerasus Pseudocerasus)

As an ancient cultivated fruit tree,Chinese cherry(Cerasus pseudocerasus(Lindl.)G Don)belongs to genera Cerasus,subfamily Prunoideae,family Rosaceae,which has the advantages of early blossom,high ornamental and nutritional values,rich flavor and strong disease resistance.It originated in Southwest China and widely distributed in various provinces and cities in China,including local varieties,some large-scale cultivars and wild populations.There is a long history of its cultivation,which can date back to 3000 to 4000 years ago.The flowering peroids of Chinese cherry is from March to April,setting fruits from May to June.Chinese cherry is one of cherry cultivars and play an important role in rural revitalization strategyBased on previous studies,Chinese cherry are polyploids in general,and almost are tetraploids.However,the origin of polyploid Chinese cherry remains unclear.Because of small chromosomes(often<3 ?m)and similar morphology,the chromosomal homology/heterologism cannot be identified by classic karyotyping and meiosis analysis of pollen cell.In this study,we intend to study the ploidy levels and chromosome number of the seedling progenies,and illustrate the origin of polyploid Chinese cherry.Karyotype analysis and rDNA distribution research provide evidence for chromosomal homology of Chinese cherry,establishing theoretical foundation for interspecies breeding.The main results of this study are listed as followsi Ploidy levels of polyploidy Chinese Cherry progenies.The chromosome number of self-pollinated progeny of eight tetraploid and one hexaploid Chinese cherry germplasms,and two tetraploid Chinese cherry natural pollinated were examined in this study.Among forty tetraploid Chinese cherriy self-pollinated seeds,tetraploid,pentaploid,and hexaploid were found in twenty-four,two and one seeds,which accounted for 85%,5%and 2.5%.In addition,aneuploid was also observed in two and one seeds with 33 and 47 chromosomes.As for fourteen seeds of self-pollinated progeny of hexaploid Chinese cherry,majority of seeds were hexaploid,accounting for 62.29%,and minority of seeds were pentaploid with the proportion of 28.57%.Similarly,we also found an aneuploid with ploidy level of 2n=6x+1=49.Within fifty-three tetraploid cultivated and wild Chinese cherry naturally pollinated seeds,most of them were tetraploid and pentaploid,which accounted for 73.58%and 18.87%,respectively.Only two seeds were hexaploid,and no aneuploid was found.In summary,there were various ploidy levels including tetraploid,pentaploid,hexaploid and aneuploid among tetraploid Chinese cherry progenies.This indicated that gametes after meiosis formed containing three chromosome complements.It was speculated that univalent and trivalent formed after pairing and separation of homologous chromosomes during meiosis.Correspondingly,bivalents and tetravalents formed after chromosome pairing and separation of meiotic in hexaploid Chinese cherry,resulting in the formation of pentaploids by the fusion of diploid and triploid gametes.On the contrary,homologous polyploids are more likely to form multivalents after meiosis.Combining these facts,the chromosome complements of Chinese cherry shared relatively high homology,which suggested that polyploid Chinese cherry is more likely to be autoploid.ii karyotype of Chinese cherry and relatives.The karyotypes of seventy-seven metaphase cells from five Chinese cherry local cultivars and one wild Chinese cherry were analyzed.The karyotype formula of tetraploid and hexaploid Chinese cherry was characterized by 2n=4x=32=24m+8sm and 2n=6x=48=42m+6sm.The chromosomes consisted of mainly median chromosome(m)and few submedian chromosomes(sm),accounting for 81.25%and 18.75%,respectively.The absolute length of the chromosome ranged from 1.54 to 5.03 ?m with the average arm ratio from 1.33 to 1.46.The longest to shortest chromosome ratio was from 2.01 to 2.39.The karyotype was 1B with asymmetry coefficient ranging from 56.98%to 65.82%.iii the distribution of rDNA and chromosome recognization.5S and 18S rDNA were used to recongize chromosome of PD 3(2n=5x,6x=40,48)and BZ(wild,2n=4x,5x=32 40)by fluorescence in situ hybridization(FISH)technique.5S rDNA located at the peri-centromeric region of short arm in chromosomes 4 and 5.Twelve,ten and eight 5S rDNA loci were observed in hexaploid,pentaploid and tetraploid,respectively.18S rDNA signals located at the satellite of short arms in Chr.4 and 7,which revealed high polymorphism.Eight signals were detected in tetraploid Chinese cherry,and nine were detected in pentaploids at most.Thus,the karyotype analysis and physical location of rDNA sites provided reference for the identification of Chr.l,4,5 and 7.Chromosome structural variation and break or loss of satellites had high possibility,resulting in the number polymorphism of 18S rDNAIn conclusion,pentaploid and hexaploid were observed,as well as aneuploid among tetraploid self-pollinated seedlings.It was more likely that Chinese cherry was autopolyploid.Karyotype analysis and rDNA distribution showed relatively low possibility of allopolyploid.Therefore,polyploid Chinese cherry is autoploid with high homology of chromosome sets.