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This article in CS

  1. Vol. 25 No. 3, p. 497-501
    Received: Mar 19, 1984

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Nitrate Effect on Nodulation of Soybean by Bradyrhizobium japonicum1

  1. A. H. Gibson and
  2. J. E. Harper2



It is not known whether NO3 inhibition of nodulation is primarily due to effects on the host plant or on the bacterials train. This study was conducted to evaluate the effect of NO3 on nodule appearance and development of nitrogenase (acetylene reduction) activity of various Glycine max (L.) Merr. cultivar ✕ Bradyrhizobiumja ponicum (Kirchner) Buchanan strain combinations. Plants were grown hydroponically in controlled environment cabinets. NO3 was either resupplied daily (“maintained”) during the growth period or allowed to deplete with plant growth (“rundown”). Nodule development was delayed all NO3 treatment conditions (both maintained and rundown), the delay being more severe at higher NO3 concentrations. The external concentration of NO3 rather than the rate of NO3 uptake appeared to have a major effect on the initial stages of nodulation. Treatment conditions providing similar rates of NO3 up take from different solution NO3 concentrations( 4.0 mM rundown vs . 0.5. mM maintained) resulted in a more marked inhibition of nodule appearance at the higher level of solution NO3. Maintaining the solution concentration of NO3 at 1.0 mM following the appearance of nodules greatly retarded, or prevented, the development of nitrogenase activity (C2H2 reduction). Minor differences in the tolerance of nodulation to NO3 were observed among eight B. j. uponicum strains (preselected from 46 strains). More variation existed among 12 soybean cultivars (preselected from 23 cultivars) with respect to their ability to nodulate in the presence of NO3. The cvs. Elf and Avoyelles were notable in having good nodulation tolerance to NO3 when infected by USDA110. This indicated that, with selection and breeding, enhanced NO3 tolerance of nodulation between soybean and B. japonicum should be possible.

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