Compatible rhizobia strains are essential for nodulation and biological nitrogen fixation (BNF) of hairy vetch (Vicia villosa Roth, HV). We evaluated how past HV cultivation affected nodulation and BNF across host genotypes. Five groups of similar HV genotypes were inoculated with soil dilutions from six paired fields, three with 10-year HV cultivation history (HV+) and three with no history (HV-), and used to determine efficiency of rhizobia nodulation and BNF. Nodulation was equated to nodule number and mass, BNF to plant N and Rhizobium leguminosarum biovar viceae (Rlv) soil cell counts using qPCR to generate an amplicon of targeted Rlv nodD genes. Both HV cultivation history and genotype affected BNF parameters. Plants inoculated with HV+ soil dilutions averaged 60 and 70 % greater nodule number and mass, respectively. Such plants also had greater biomass and tissue N than those inoculated with HV- soil. Plant biomass and tissue N were strongly correlated to nodule mass (r 2 = 0.80 and 0.50, respectively), while correlations to nodule number were low (r 2 = 0.50 and 0.31, respectively). Although hairy vetch rhizobia occur naturally in soils, past cultivation of HV was shown in this study to enhance nodulation gene-carrying Rlv population size and/or efficiency of rhizobia capable of nodulation and N fixation.
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Acknowledgments Funding for this project was provided by a Fulbright Grant to graduate student Nape Mothapo. Thanks to farmers, Alex Hitt, Ken Dawson, Michael Fortune, Michael Porterfield, and Stephan Hartman, for making their fields available for the project and sharing their farm management information. The authors acknowledge Dr. Peter Young for providing standard rhizobia strains, Dr. Consuelo Arellano for assisting with statistical analyses, and Drs. Chris Reberg-Horton and Daniel Israel for reviewing the manuscript.
- Biological nitrogen fixation (BNF)
- Hairy vetch
- Rhizobium leguminosarum biovar viciae (Rlv)