Rhizobial diversity is associated with inoculation history at a two-continent scale

Abstract

A total of 120 Mesorhizobium strains collected from the central dry zone of Myanmar were analysed in a pot experiment to evaluate nodulation and symbiotic effectiveness (SE%) in chickpea plants. Phylogenetic analyses revealed all strains belonged to the genus Mesorhizobium according to 16-23S rDNA IGS and the majority of chickpea nodulating rhizobia in Myanmar soils were most closely related to M. gobiense, M. muleiense, M. silamurunense, M. tamadayense and M. temperatum. Around two thirds of the Myanmar strains (68%) were most closely related to Indian strain IC-2058 (CA-181), which is also most closely related to M. gobiense. There were no strains that were closely related to the cognate rhizobial species to nodulate chickpea: M. ciceri and M. mediterraneum. Strains with diverse 16S-23S rDNA IGS shared similar nodC and nifH gene sequences with chickpea symbionts. Detailed sequence analysis of the nodC and nifH found that the strains in Myanmar were somewhat divergent from the group including M. ciceri and were more closely related to M. muleiense and IC-2058. A cross continent analysis between strains isolated in Australia compared with Myanmar found that there was little overlap in species, where Australian soils were dominated with M. ciceri, M. temperatum and M. huakuii. The only co-occurring species found in both Myanmar and Australia were M. tamadayense and M. silumurunense. Continued inoculation with CC1192 may have reduced diversity of chickpea strains in Australian soils. Isolated strains in Australian and Myanmar had similar adaptive traits, which in some cases were also phylogenetically related. The genetic discrepancy between chickpea nodulating strains in Australia and Myanmar is not only due to inoculation history but to adaptation to soil conditions and crop management over a long period, and there has been virtually no loss of symbiotic efficiency over this time in strains isolated from soils in Myanmar.

Contribution of Biofertilizers to Pulse Crops: From Single-Strain Inoculants to New Technologies Based on Microbiomes Strategies

“…As expected, the isolates did not show cross-nodulation with four other pulses ( P. vulgaris , P. sativum , L. culinaris, and V. mungo ). In the major soil areas of Myanmar, chickpea nodulating rhizobia are most closely related to Mesorhizobium gobiense , Mesorhizobium muleiense , Mesorhizobium silamurunense , Mesorhizobium tamadayense, and Mesorhizobium temperatum [ 64 ]. Around two-thirds of the strains were close to M. gobiense , which also represents a common Indian strain CA-181 already mentioned by Singh et al [ 63 ].…”