Genetic Diversity, Evolution And Fingerprinting Of Cultivars (Brassica Napus) In China

Analysis of genetic diversity, study on genetic evolution and fingerprinting of 130 elite Brassica napus cultivars which were bred in different periods in China and introduced from abroad were carried out with SRAP and SSR. Results can be drawn from this study as followings.1. The number of amplified fragments and polymorphic fragments per primer combination were 20.4 and 4.9, respectively. The percentage of polymorphic fragments was 24%. Results showed that SRAP markers were effective, inexpensive and dependable.2. One hundred and thirty B. napus accessions were divided into four groups A, B, C and D at the genetic distance 0.12. About 78.5% accessions were classified into group C. Group C also could be divided into â… ,â…¡,â…¢, â…£ and â…¤ sub-groups at genetic distance 0.10. About 58.5% accessions were included into sub-group â…¢, indicating the genetic diversity of about 58.5% accessions was poor.3. The results demonstrated that the genetic basis of B. napus L. accessions released before 1980 was the narrowest and they reached to the widest in next decade. In the 1990's, the genetic distances declined. The genetic basis decreased further after 2000. Except for the difference of mean genetic distance between the accessions bred in 1990's and those after 2000 did not reached sgnificant level, the other differences of mean genetic distance among different periods reached significant leve.The difference of mean genetic distances between the accessions bred in China and those introduced from abroad reached significant level.4. Both every assay unit of SRAP and SSR generated about the same number (4.9) of polymorphic bands. The genetic distances between B.napus accessions revealed with SRAP markers were less than those revealed with SSR markers. The correlation efficient between the two molecular marker systems was low (r=0.2365), but it reached significant level (p<0.01).5. Two phylogenetic trees were constructed with SRAP and SSR using MEGA version 2.1.All these 130 B.napus accessions were divided into 11 evolutionary groups in both of SRAP and SSR phylogenetic trees. However, the accessions included in relative evolutionary groups were different. The evolutionary relationship in SRAP phylogenetic tree was closer to the pedigrees of accessions than that in SSR phylogenetic tree.6. The divergence time of spring biotype accessions was the shortest and that of winter accessions was the longest. The divergence time difference between them reached to significant level at 0.05. The divergence time of semi-winter accessions...