Genetic Diversity Of Rhizobia Associated With Medicago Sativa In Two Ecological Regions Of China

Alfalfa has been widely planted in the east and northeast regions of China,according to the rapid development of livestock,.A total of 114 strains of rhizobia were collected from 13 sites located in these new developed regions including Heilongjiang,Jilin,Liaoning,Inner mongolia,and Anhui.Genetic diversity of the isolates and their correlations with soil factors were analyzed in this study,in order to understand the population structure of alfalfa rhizobia in these regions and their main environmental impact factors.The results would not only provide rich germplasm resources for screening effective alfalfa rhizobia inoculants but also lay a scientific basis for further exploration of evolutionary mechanism in rhizobia.Different inactivation methods of rhizobium carried by alfalfa seeds were compared,the result suggested that rhizobium inside the seeds can be inactivated under 6 consecutive days of 70? dry treatment.This method can provide technical support for subsequent studies such as rhizobium capture from soil and rhizobium inoculation.Based on the results of IGS rRNA gene PCR-RFLP,114 bacterial strains can be divided into 12 IGS types.16S rRNA gene sequence alignment of representative strains indicated that some IGS groups were restricted in Anhui province while some were restricted in the northeast region.112 isolates belong to Sinorhizobium meliloti which is the dominant species in two regions.The other two isolates are Rhizobium alkalisoli and R.gallicum,which was firstly isolated from Medicago nodules in China.Clustering analysis showed that genetic distance is far between R.alkalisoli,R.gallicum and S.meliloti,S.medicae.The Correlation analysis between rhizobial IGS types and soil factors suggest that pH value,organic matter,total nitrogen,effective nitrogen,conductivity and Na+content in soil play the most important roles in rhizobial IGS types in northeast and easten China.In northeast China,high level of soil organic matter,total nitrogen and soil Na+ content condition can be beneficial for IGS type 10,while high effective nitrogen,high available potassium and conductivity benefits for type 1 and 9.Meanwhile,IGS type in eastern areas showed positive correlation to soil pH,while it showed negtive correlation with soil organic matter,total nitrogen and soil Na+content.