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Aims: To describe the chickpea rhizobial diversity in Gansu Province of China, so far uninvestigated. Methods: Nodule bacteria were isolated from chickpea grown in Gansu and characterized by phylogenetic analysis of 16S rRNA gene, housekeeping genes ( atpD, recA, and glnII), and symbiotic genes ( nodC and nifH). The genetic differentiation and gene flow among the chickpea microsymbionts were estimated and considered in view of soil characteristics. Results: A total of nineteen new isolates originating from alkaline-saline (pH 7.9-8.1) soils in Gansu formed two clades by housekeeping gene analyses; clade I (16 isolates) was identified as Mesorhizobium muleiense (97.7-98.7 % of similarities with the type strain CCBAU 83963) and clade II (3 isolates) formed a separate group within Mesorhizobium branch, displaying 97.0 and 96.6 % similarities with the most related type strains M. temperatum SDW 018 and M. muleiense CCBAU 83963, respectively. Their symbiotic genes ( nodC and nifH) were highly similar (>98.0 %) with those described for chickpea microsymbionts in literature, i.e., M. muleiense, M. ciceri, and M. mediterraneum. The genetic differentiation and gene flow between the chickpea rhizobial groups supported our conclusions for species affiliation. Conclusions: M. muleiense and a novel Mesorhizobium genospecies, sharing similar symbiotic genes, are distributed in the alkaline-saline soils of Gansu and may be considered as the main and specific chickpea symbionts in the Northwest of China. [ABSTRACT FROM AUTHOR]

Diversity and taxonomic affiliation of chickpea rhizobia were investigated from Ningxia in north central China and their genomic relationships were compared with those from northwestern adjacent regions (Gansu and Xinjiang). Rhizobia were isolated from root-nodules after trapping by chickpea grown in soils from a single site of Ningxia and typed by IGS PCR-RFLP. Representative strains were phylogenetically analyzed on the basis of the 16S rRNA, housekeeping (atpD, recA and glnII) and symbiosis (nodC and nifH) genes. Genetic differentiation and gene flow were estimated among the chickpea microsymbionts from Ningxia, Gansu and Xinjiang. Fifty chickpea rhizobial isolates were obtained and identified as Mesorhizobium muleiense. Their symbiosis genes nodC and nifH were highly similar (98.4 to 100%) to those of other chickpea microsymbionts, except for one representative strain (NG24) that showed low nifH similarities with all the defined Mesorhizobium species. The rhizobial population from Ningxia was genetically similar to that from Gansu, but different from that in Xinjiang as shown by high chromosomal gene flow/low differentiation with the Gansu population but the reverse with the Xinjiang population. This reveals a biogeographic pattern with two main populations in M. muleiense, the Xinjiang population being chromosomally differentiated from Ningxia-Gansu one. M. muleiense was found as the sole main chickpea-nodulating rhizobial symbiont of Ningxia and it was also found in Gansu sharing alkaline-saline soils with Ningxia. Introduction of chickpea in recently cultivated areas in China seems to select from alkaline-saline soils of M. muleiense that acquired symbiotic genes from symbiovar ciceri., (Copyright © 2020 Elsevier GmbH. All rights reserved.)