Symbiotic efficiency, rhizosphere competence and nodule occupancy of chickpea root-nodule bacteria from Australian soils

Abstract

Abstract Aims: To evaluate the suitability of novel chickpea rhizobia for use as commercial chickpea inoculants Methods: Root nodule bacterial isolates from field grown chickpea were evaluated in glasshouse and field experiments based on infectivity, relative symbiotic effectiveness nodule occupancy ability and survivability in the soil rhizosphere. Results: Compared to the Australian commercial chickpea inoculant strain Mesorhizobium ciceri sv. ciceri CC1192, the 10 novel strains were fast growers, taking ~ 72 hours to grow at 23oC. The strains showed high degree of infectivity and effectiveness both in the glasshouse and field. Relative symbiotic effectiveness (RSE%) of the novel strains in glasshouse experiments determined by shoot weight ranged from 77-111% in Desi genotype (Kyabra) and 83-102% in Kabuli (Kimberley Large). None of the novel strains differed from CC1192 in total shoot N content. Except for strain 3/4 and M. ciceri sv. ciceri CC1192, the RP01 RAPD fingerprint profiles of the strains were variable and diversity among strains did not correlate to their source of origin. A phylogenetic comparison of the cloned 16S rRNA sequences identified M. ciceri LMG 14989 as the most common distant relative to all strains. Also, the strains were able to survive in soil rhizosphere, had a higher competitive ability and were able to compete with background rhizobia population for nodule occupancy. Conclusions: There are several rhizobial strains in naturalised soil populations that may be better adapted to local soil conditions which would confer an advantage for survival and competition for nodulation.