Analysis of genetic diversity and population genetic structure of Medicago archiducis-nolai and Medicago ruthenica populations based on cpDNA trnL-trnF sequences

Genetic diversity and population genetic structure of seven Medicago archiducis-nicolai and three M. ruthenica populations distributed at Qinghai-Tibet plateau(QTP)or adjacent areas and Inner Mongolia were analyzed. The results showed that, 11 polymorphic sites were detected based on the alignment of 161 trnL-trnF fragments, 14 haplotypes were identified(H1~H14). Analysis of genetic diversity and distribution of haplotypes in each population showed that the southeast edge of the Qinghai-Tibet plateau might be a refugia for M. archiducis-nicolai and gene invasion could happened across M. archiducis-nicolai to M. ruthenica in this area. Both spatial analysis of molecular variance and N-J clustering of populations based on K-2P genetic distance divided the 10 populations into two groups, that is, M. archiducis-nicolai and M. ruthenica. Analysis of molecular variation suggested that most of the genetic variation existed within populations, high population differentiation was found among some populations. Both of the two species did not experience recent population expansion based on mismatch distribution and neutrality tests. These results suggested that the genetic structure of the two species might be caused by complex topography and climate oscillations during glacial periods of the QTP. The evolutionary history of these species could also play an important role.