| 1. Genetic diversity analysis of B. napus genome using SSRIn order to know the genetic alterations of rapeseed cultivars, in this study the genomic diversity was analyzed among 110 B. napus varieties released in different time revealed with SSR. The results are as follows:1) 93 out of 105 primer pairs (91.3%) amplified a total of 213 polymorphic loci with an average of 2.3 per primer combination and 67 pairs of which were evenly distributed in 19 A and C genome linkage groups.2) The average Nei diversity index of 19 linkage group was 0.239 and Shannon diversity index was 0.377. However, the extent of variation is different in chromosomes. The variation of A genome in semi-winter rapeseed was larger than C genome.3) The genetic distance within semi-winter, winter and spring accessions was 0.384,0.180 and 0.168, respectively.4) Genetic diversity of Chinese semi-winter B. napus classified into four periods (before 1980, 1980-1990,1991-2000, and after 2001), showed that genetic diversity index was minimum in before 1980, which was consistent with the actual situation. Relatively low genetic coefficient of differentiation among 4 populations based Nei’s gene diversity (0.1257), and estimation of gene flow (3.4781) indicates that the genetic variations mainly came from the individuals, rather than populations. Cluster analysis showed that Chinese semi-winter rapeseed could be divided into two groups:accessions revealed before 1980 and after 1980.2. Screening of core simple sequence repeat primer pairsBrassica is an important oil crop. Recently, simple sequence repeat (SSR) markers have become preferred molecular markers due to their simplicity, high levels of polymorphism, and codominant nature. Numerous SSR markers have been developed in Brassica crops, but not every SSR marker has an equal value, they must be tested individually for each application. As a consequence, it is necessary to collect a set of standard and high quality SSR markers. In addition, core primer pairs were 3-5 times higher than the PCR amplification of single primer pairs and improve the efficiency of molecular markers in Brassica species, with no additional cost. The results were as follows:1) To develop a set of standardized, highly efficient core SSR primers,190 primer pairs evenly separated in 19 chromosomes of rapeseed were chosen from 2353 SSR primer pairs that have been used to map in Brassica species.2) We also established 19 multiplex polymerase chain reaction (PCR) combinations, one per linkage group. Twenty accessions from six Brassica species were used to test these primer combinations and an average of 15 clear bands were amplified successfully in each reaction.3) 20 materials were classified by using clustering analysis. The results showed that 20 accessions were divided into six groups, five B. rapa in classⅠ, three wild B. oleracea in classⅢ, one wild B. oleracea and one resynthesis B. napus in classⅢ, five cultivated B. oleracea in classⅣ, B. napus in classⅤ, wild B. oleracea, Brassica cretica subsp. Laconica in classⅥ. |
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