Symbiosis of selected Rhizobium leguminosarum bv. viciae strains with diverse pea genotypes: effects on biological nitrogen fixation.

Biological nitrogen fixation (BNF) can be improved by optimizing the interaction between the rhizobial inoculant and pea (Pisum sativum L.), leading to increased productivity and reduced nitrogen (N) fertilizer use. Eight Rhizobium leguminosarum bv. viciae strains were used to inoculate the super-nodulating pea mutant Rondo-nod3 (fix+), the hyper-nodulating pea mutant Frisson P88 Sym29, CDC Meadow commercial control, and the non-nodulating mutant Frisson P56 (nod-) to evaluate BNF in a greenhouse assay. Significant differences in strain × cultivar interactions were detected for shoot and root dry masses, which ranged from 1.8 to 4.7 g and from 0.27 to 0.73 g per plant, respectively; for nodule number on lateral roots, which ranged from 25 to 430 per plant; for amount of fixed N2 , which ranged from 15 to 67 mg and from 4 to 15 mg per plant for shoot and root tissues, respectively; and for percentage of N derived from atmosphere (%Ndfa), which ranged from 37% to 61% and from 35% to 65% for shoot and root tissue, respectively. Strain × cultivar interactions in this study could contribute to identification of superior strains and pea breeding lines with genetic superiority in BNF. Nodule production in pea plants was not necessarily correlated with the amount of fixed N2 , suggesting nodule activity is more important to BNF than is nodule number.