Single and Multistrain Rhizobial Inocula for Pinto and Black Bean Cultivars

ABSTRACT

Common bean (Phaseolus vulgaris L.) is relatively poor in dinitrogen (N₂) fixation, so selecting compatible host cultivar and Rhizobium strain combinations may offer an improvement. The effectiveness of six rhizobial strains was evaluated using five bean cultivars of bean (three pinto and two black bean) in a growth-room experiment. We subsequently selected the three best strains to assess whether multi-strain inoculation had advantages over single-strain inoculation in growth-room and field experiments. In the first-growth-room experiment, Rhizobium strains UMR 1899, RCR 3618, and USDA 2676 were selected for high nodulation, plant dry weight, shoot nitrogen (N), and N₂ fixation. In a second growth-room experiment, the individual strains and a mixture of the three strains generally did not differ in the parameters evaluated. Total shoot N accumulated ranged from 172.9 to 162.8 mg plant⁻¹, of which 32.1% to 33.6% (equivalent to 54.0 to 59.2 mg plant^{− 1}) was fixed. In field experiments, plant biomass and seed N₂ fixed did not differ among the inoculants at any site. These results suggest that the three strains were equally effective and that the multi-strain inoculant offered no consistent advantage over the single-strain inoculants.

Keywords:

• Rhizobium
• inoculation
• nodulation
• nitrogen fixation

ACKNOWLEDGMENTS

We are grateful to the Saskatchewan Pulse Growers for financial support. We also thank MicroBio RhizoGen Corp., Saskatoon, for formulating the Rhizobium inoculants. The technical assistance of Erin Lindenbach is greatly appreciated.

Notes

^a Mixture = UMR 1899 + RCR 3618 + USDA 2676.

^a Mixture = UMR 1899 + RCR 3618 + USDA 2676.

^a Mixture = UMR 1899 + RCR 3618 + USDA 2676.

^a Mixture = UMR 1899 + RCR 3618 + USDA 2676.