Hairy vetch (Vicia villosa Roth, HV) is widely grown as a legume cover crop throughout the U.S.A., with biological nitrogen fixation (BNF) through symbiosis with Rhizobium leguminosarum biovar viciae (Rlv) being one of the most sought after benefits of its cultivation. This study determined if HV cultivation history and plant genotype affect genetic diversity of resident Rlv. Soil samples were collected from within farmers' fields at Graham, Cedar Grove and Ivanhoe sites in North Carolina and pairs of genetically similar hairy vetch genotypes used as trap hosts. A total of 519 Rlv strains were isolated from six paired field soils, three with and three without histories of HV cultivation. A total of 46 strains failed to PCR-amplify the nifH gene; however nodC PCR amplification of these nifH-negative strains resulted in amplification of 22 of the strains. Repetitive element polymerase chain reaction (rep-PCR) with BOX-A1R primer and redundancy analysis showed rhizobial diversity to vary greatly within and between fields, with over 30 BOX banding patterns obtained across the six fields. Cluster analysis of BOX-PCR banding patterns resulted in 36 genetic groups of Rlv at a similarity level of 70%, with 15 of the isolates from fields with HV history not belonging to any of the clusters. Site was found to be the main driver of isolate diversity overall, explaining 57%, of the total variation among rhizobia occupying HV nodules, followed by history of hairy vetch cultivation. Evidence of a HV host genotype influence on the populations of rhizobia that infect hairy vetch was also observed, with plant genotype explaining 12.7% of the variation among all isolates. Our results show that second to site, HV cultivation history was the most important driver of rhizobial nodule community structure and increases the genetic diversity of resident Rlv in soils.
Bibliographical noteFunding Information:
Farmers, Alex Hitt, Ken Dawson, Michael Fortune, Michael Porterfield and Stephan Hartman, are appreciated for making their fields available and willingly sharing their farm management information to help with the project. Funding support from a Fulbright Scholarship and the USDA-SARE program is greatly appreciated.
- Cropping history
- Genetic diversity
- Hairy vetch
- Rhizobium leguminosarum bv. viciae