Genetic Diversity And Phylogenetic Relationship Among Chinese Mustard As Revealed By RAPD And Microsatellite Markers

The genetic diversity of 29 Brassica juncea accessions was investigated using RAPDs and microsatellite markers. The two assays differed in the amount of polymorphism detected. Microsatellites detected a higher average polymorphism of 82.1% than the average polymorphism of 73.83% detected by RAPDs markers. A total of 101 polymorphic bands with an average of 7.21 bands per primer pair were generated by 11 microsatellite primer pairs. 124 polymorphic bands were amplified by 22 arbitrary primers with an average of 5.64 bands per primer. Two genetic similarity matrices were estimated based on band presence or absence. Genetic diversity trees (dendrograms) were derived from individual marker of RAPDs and SSR and compared using SAS software test. The correlation coefficient was 0.8869 between RAPDs and SSR markers. Another dendrogram was constructed based on the combined data of the two molecular markers. It gave a better classification result than any individual marker.According to the results of RAPDs analysis, accession 1 and 3 which belong to root mustard were clustered into a minor group, accession 4 and 6 which are both long stem mustard were in a minor group; accession 7, 8 and 9 which belong to stem mustard were in a minor group; accession 12, 14 and 15 which were all broken-leaf mustard were clustered into a minor group; accession 16, 19 and 26 which had similar heading tendency were clustered into a minor group; Genetic distance among the 33 accessions in average was 0.523, the maximum one 0.834 is between accession 3 and 31, and the minimum one 0.098 is between accession 19 and 26.Two main groups were formed by the cluster analysis based on microsatellite, three root mustards of accession 1, 2 and 3 were clustered into one of the two groups, and in the other main group, three sprout mustards were in a minor group; two accessions of 16 and 19 which had heading tendency were in a minor group; two stem mustard accessions of 7 and 9 were clustered into a minor group. Dfferently from the result of RAPDs analysis, one accession of 32 which belong to Brassica rapa show a close relationship with accession 31 instead of accession 30. The genetic didtance among the 33 accessions in average was 0.638, the maximum one 0.859 between accession 4 and 31 and the minimum one 0.099 between accession 16 and 19.The molecular classification of of leaf mustard accessions was different from the classification from morphorlogical method. And the seed mustard of accession 25, which was aunique one, was not in same position in the dendrograms obtained from the two molecular markers.The two methodologies gave different views of the amount of variation present, but both of them showed a high level of genetic variation in Brassicajuncea. The following conclusions can be drawn from this study whether based on RAPDs data or microsatellite data: (i) the degree of genetic variation within the studied accessions was notably great and (ii) several groups of accessions which had similar phenotype were consistently revealed by the dendrograms generated by RAPDs and microsatellites data. The accessions with similar morphological characteristic always had a close relationship. The traditional classification of Brassica juncea was partly in accordance with the result made by molecular data. In other words, the morphorlogical characteristic difference could indicate some of their genetic background difference, (iii) Chinese mustard crops have closer relationships with one of their ancient parental species Brassica rapa (iv) The DNA-based markers will be more useful in detecting genetic diversity in closely related accessions but the capicity of different molecular markers for classifying the genetic relationship of closely related accessions were different. In addition, a dendrogram that took into account all fragments produced by RAPDs and microsatellites reflected better the relationships than did dendrograms based on only one type of markers.