The Search for Acid-tolerant Rhizobia to Improve Pulse Production

Soil acidification is a growing challenge in Washington’s agricultural soils due to long term application of ammonia-based fertilizers. Acidic soil is detrimental to legume-rhizobia symbioses and nitrogen fixation. We seek to find acid tolerant and effective strains of Mesorhizobium spp. and Rhizobium leguminosarum, which associate with chickpeas and dry peas/lentils, respectively. The ultimate mission of this research is to maintain or increase production and biological nitrogen fixation of three major Washington pulse crops despite unfavorable and worsening soil conditions.

Eighty putative isolates of M. ciceri and 103 putative R. leguminosarum bv. viciae from chickpeas and lentils growing in Palouse area soils were studied. Thirty percent of M. ciceri isolates and 69% of R. leguminosarum were moderately tolerant of pH 5.5, but only 7% and 17%, respectively, were even slightly tolerant of pH 4.5 in laboratory tests. Robust analysis of six regions of bacterial DNA, determined that 20 unique R. leguminosarum and 34 unique M. ciceri have been collected. With this information, the unique and more acid-tolerant isolates have been identified for further studies in soil conditions. The slide into acidified soil conditions in the Palouse is likely to dramatically reduce the growth and survival of most of the current rhizobial symbionts of our pulse crops.

Grant Information

  • Project ID: 143
  • Project Status: Complete


  • Principal Investigator(s): Carpenter-Boggs, L.
  • Investigator(s): McGee, R., Vandemark, G.
  • Grant Amount: $38,557
  • 2015 Progress Report (PDF)


Piaskowski, J., G. Vandemark, N. Pierre-Pierre, L. Carpenter-Boggs. Diversity of Mesorhizobium ciceri and Rhizobium leguminosarum in soils of the Palouse region. In preparation.

Additional Funds Leveraged

Additional funds have been requested from the US Dry Pea and Lentil Council and the USDA-ARS Postdoctoral Research Associate Program. We are also preparing for application to the NIFA Foundational Program in 2017 (Plant Health and Production and Products).


• Short-Term:
The acid tolerance information on these isolates is useful information for characterizing the rhizobial collection held jointly by WSU and the USDA-ARS. These data have been matched with DNA sequence information on the isolates for use by other researchers. A genetically and functionally diverse array of isolates will be entered to the National Rhizobial Collection for use by other researchers. The information generated by this line of study will expand knowledge about the strains, conditions, and nutritional supplements that can improve survival of rhizobia and nitrogen fixation in acidic soils.
• Intermediate-Term:
With further laboratory, greenhouse, and field testing, new inoculants and amendments are foreseen that support and increase nitrogen fixation in acidic soils. The value of nitrogen fixation per year can be $20 – $60 per acre in conventionally fertilized fields or over $500 per acre in organic production. Use of nitrogen fixing crops in rotation also reduces the use of additional nitrogen fertilizers which have a worse acidifying effect.
• Long-Term:
This study is part of a longer term effort to characterize existing populations of rhizobial bacteria that associate with legumes grown in the Palouse, and to improve inoculants and amendments for conditions found in soils of the PNW. The long term effect will be maintained or improved diversity of cropping rotations including chickpeas, peas, and lentils; improved nitrogen fixation in acidic soils, and improved environmental and economic sustainability.