title: Genetic diversity and distribution of rhizobia associated with the medicinal legumes Astragalus spp. and Hedysarum polybotrys in agricultural soils.
abstract: With the increasing cultivation of medicinal legumes in agricultural fields, the rhizobia associated with these plants are facing new stresses, mainly from fertilization and irrigation. In this study, investigations on the nodulation of three cultivated medicinal legumes, Astragalus mongholicus, Astragalus membranaceus and Hedysarum polybotrys were performed. Bacterial isolates from root nodules of these legumes were subjected to genetic diversity and multilocus sequence analyses. In addition, the distribution of nodule bacteria related to soil factors and host plants was studied. A total 367 bacterial isolates were obtained and 13 genospecies were identified. The predominant microsymbionts were identified as Mesorhizobium septentrionale, Mesorhizobium temperatum, Mesorhizobium tianshanense, Mesorhizobium ciceri and Mesorhizobium muleiense. M. septentrionale was found in most root nodules especially from legumes grown in the barren soils (with low available nitrogen and low organic carbon contents), while M. temperatum was predominant in nodules where the plants were grown in the nitrogen-rich fields. A. mongholicus tended to be associated with M. septentrionale, M. temperatum and M. ciceri in different soils, while A. membranaceus and H. polybotrys tended to be associated with M. tianshanense and M. septentrionale, respectively. This study showed that soil fertility may be the main determinant for the distribution of rhizobia associated with these cultured legume plants.
authors.affiliation: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Yan
authors.affiliation: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China.
authors.forename: Zhao Jun
authors.initials: ZJ
authors.lastname: Ji
authors.affiliation: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China.
authors.forename: Yin Shan
authors.initials: YS
authors.lastname: Jiao
authors.affiliation: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China; Departamento de Microbiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, 11340 México D.F., Mexico.
authors.forename: En Tao
authors.initials: ET
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China. Electronic address: chenwf@cau.edu.cn.
authors.forename: Wen Feng
authors.initials: WF
authors.lastname: Chen
authors.affiliation: Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100193, China.
authors.forename: Bao Lin
authors.initials: BL
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China.
authors.forename: Wen Xin
authors.initials: WX
authors.lastname: Chen
mesh_terms: D021903:DNA, Ribosomal Spacer; D007887:Fabaceae / Q000382:microbiology*; D014644:Genetic Variation; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012231:Rhizobium / Q000145:classification* / Q000235:genetics*; D053204:Root Nodules, Plant / Q000382:microbiology; D012988:Soil Microbiology; D013559:Symbiosis
chemical_list: D021903:DNA, Ribosomal Spacer; D012336:RNA, Ribosomal, 16S
keywords: Astragalus; Distribution; Genetic diversity; Mesorhizobium; Rhizobia