Meiotic Observations On The Pollen Mother Cells Of Ziziphus Jujuba Mill And Ploidy Identification Of The Cultivar ’pingguozao’

Chinese jujube originated in China belongs to Ziziphus genus, Rhamnaceae family. Itis a special advantage fruit tree in China and has a long cultivation history and widedistribution.‘Zanhuangdazao’shows the advantages of polyploid, such as huge fruit,well-adapted, the rich nutrition and high yield. Polyploid breeding is one of the effectiveways of germplasm innovation,2n gametes is the most widely way applied in Sexualpolyploidization breeding. This experiment wants to reveal the formation mechanism of2npollen in Chinese jujube, via cytology observation and statistical of abnormal meiosisphenomenon of pollen mother cell. What’s more,a new natural triploid jujube,‘Pingguozao’ is identified. These experiments may bring data for cytological studies ofjujube, polyploid breeding, and application of germplasm. The main results were asfollows:1.‘Linglingzao’ and ‘Fupingdazao’ as experimental materials in this research wereused to observe the meiosis course of pollen mother cells in detail. Abnormal phenomenonwas founded in the meiosis course of the two jujube cultivars. These anomaly mainlyincluded: double nucleoli in diakinesis, lagging chromosomes in anaphase I and II,chromosome bridge, micronucleus, anomalous separation of sister chromatids, andparaspore in fission phases. It was founded that the abnormal phenomenon was moreobvious in ‘Linglingzao’ than ‘Fupingdazao’, especially the frequency of laggingchromosomes and chromosome Bridges.‘Fupingdazao’ had24pair of bivalent indiakinesis, but ‘Linglingzao’ had none.2. Through the statistics and analysis to spindle types in metaphaseⅡand fission typein fission phases in ‘Linglingzao’ and ‘Fupingdazao’, we found that the formationmechanism of2n pollen of two jujube was not same completely. But it mainly formed fromdyad and triad that was formed from the abnormal spindle type (three pole spindle andfusion spindle). The formation of triad rooted in three pole spindle in the meioticmetaphase Ⅱ and abnormal separation of sister chromatids in anaphase II on both theChinese jujubes. Dyad formed mainly by the parallel spindle and the fusion spindle. Inaddition to the two way of above, the2n pollen of ‘Fupingdazao’ also formed fromchromosome doubling before the meiosis. It could keep66.7%of the parents’s heterozygosity in this mechanism. The2n gametes formed by abnormal spindle canmaintain75%~83%of the parents’s heterozygosity which equaled to the type of FDR(first division restitution). The2n gametes formed by abnormal separation of sisterchromatids which equaled to the type of SDR (second division restitution). These gameteswere pure, and they could maintain33%~35%of the parents’s heterozygosity. Studiesshowed that FDR had a higher value of breeding than SDR, the most was FDR in Chinesejujube.3. The methods of eliminating walls by enzymolysis and low osmosis were used toanalyze the chromosome karyotype of Ziziphus jujuba Mill.‘Pingguozao’. The resultsshowed that the karyotype formula was2n=3x=36=21m+15sm(2SAT), and thekaryotype was2A type. It was second of the newly discovered natural triploid cultivar. Themeiosis course of pollen mother cells of ‘Pingguozao’ was observed, and the variousperiods of the meiosis were described and analyzed. The results showed that the meiosis of‘Pingguozao’ was irregular. The diakinesis appeared univalent, bivalent and trivalent, and57.5%ofthem were trivalent, at least7trivalents, at most contained10trivalents. The threegenomes had very high homology. The lagging chromosomes and chromosome unequalseparation phenomenon were observed in anaphase I and II. Some cells also produced fewtriad and pentad in Telophase Ⅱ, and formed unequal spores, and led to highlygametophyte sterility. In view of the above it was deduced that “Pingguozao” wasautotriploid. The RAPD fingerprints of ‘Pingguozao’and ‘Zanhuangdazao’ were different,which were two different natural triploid cultivars.