| A big number of new B.napus lines were resynthesized through crosses between B.oleracea var .alboglabra and local cultivars ,semi-wild or wild races of B.campestris and B.chinensis collected from Southwest of China,followed by ovary and embryo cultures and chromosome-doubling after 1986 in the Rapeseed Research Center of Sichan Agricultural University. In this paper, cytogenetic studies were made for the four resynthesized rapeseed lines with special significant characteristics :Super-long pod line H218,Big-seed line H484,Long-pod and big-seed line B25 and Many branches line Zheng 1-3.The main results obtained include:l.The viability of pollens in the studied resynthesized rapeseed lines was basically normal. The pollen viability was 82.4% for H484, was 88.0% for Zhengl-3, was 58.23% for H218. These were all lower than that of the normal B.napus cultivar ZhongYou821, the pollen viability of witch was 97.42%. The main causes of the lower pollen viability of those resynthesized rapeseed lines may be due to the cytological abnormalities appeared during the pollen mother cell meiosis.2.The following results of meiosis of these resynthesized rapeseed lines were observed :The average chromosome configuration in H484 was 1.13IV+2.33III + 12.63 II +1.20 I .Abnormal chromosome behaviors were observed during the first division ,such as multivalents and monovalent. Normal divisions were observed after anaphase I in most cells .The average chromosome configuration in H218 was 1.41 IV+2.04III + 11.43 II+3.38 I .Abnormal behaviors of chromosome were observed during the firstdivision.In PMC MI , bivalents could be rod ,ring shapes .The frequency of multivalents was 83.2%.During the second phase of meiosis there were afew cells with abnormal behaviors of chromosome.The mean chromosome paring configuration of Zhengl-3 was 1.10IV + 1.98 111 + 12.33 II +3.00 I . Abnormal behaviors of chromosome were observed during the first division .In anaphase I, Chromosome Bridge was observed in anaphase I, but normal divisions were observed in most cells in the second division.The above results indicated that the resynthesized rapeseed lines were abnormal in a high frequency during the first meiosis, but normal divisions were observed in the second division,the abnormal phenomenon had little effect on the cell growth of resythesized rapeseed. Itwas clear that the resythesized rapeseed lines in the whole were stable in cytology. It was at a relatively quick speed that the resythesized rapeseed lines in reached a stable genetic status. This may be brought about by a inhibiting gene present in the parental species ,which may restrain the pairing of the partially homologous chromosomes, and made the PMC meiosis normal.3.The karyotype of these resythesized rapeseed lines were observed with root tip cells. Their number of chromosomes were 2n=38.SAT chromosome were observed in H218and B25 .The karyotype formula of Zhengl-3 was 2n=38=2M+20m+14sm+2st .It was 2n =38=4M+20m+14sm(2SAT)for H218, 2n =38=4M+24m+2sm+2st+6T(SAT) for B25.Allthe special resythesized rapeseed lines showed "M" chromosomes. Ther were 4"M" chromosomes in in H218 and B25 ,and 2 in zheng 1-3 ."T" chromosomeswere observed only in B25,amount to 6.Obvious differences were observed in karyotypes among the resynthesized rapeseed lines,and also between the the resynthesized rapeseed lines and the nomal B.napus .Zhong you 821 ,which showed no "M"chromosomes ,but had 2 "T" chromosomes .These differences were probable come from the different patents.4. Abnormal behaviors of chromosomes were observed in all the studied resynthsized rapeseed lines .This suggested that the resynthsized rapeseed lines were sti'l in the process of evolution. Based on the standard of Stebbins , the karyotype of Zeng 1-3, B25 and ZhongYou 821 were classified as "2C"type,H218was classified as "2B"type.Those type were advanced karyotype. So these resythesised rapeseed had approached to a similar evolutional degree wth the normal B.napus for about 10 generations. Because there were still obvious diff... |
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