Legume-Rhizobium symbiosis phenotypes

We coded 771 articles published between January 1, 2009 and September 30, 2020 based on presence of relevant legume or rhizobium phenotypes. We were broadly interested in articles that quantified rhizobia and identified other relevant legume phenotypes. We used Web of Science through Chapman University to search for articles related to the legume-rhizobium symbiosis. After filtering articles for relevance, we identified 25 phenotypes present at least once in a single article, and we indicated which articles report data on that phenotype.

Methods
Web of Science Search

The Web of Science database was the chosen literature resource to obtain relevant scientific articles on the topic of interest. When finding journal articles, keywords were searched as Topic = (rhiz* OR bradyrhiz* OR mesorhiz* OR sinorhiz* OR ensifer*) AND Topic = (count* OR form* OR quant* OR estimat*) AND Topic = nod* in the search engine. Journal articles were relevant if they were published from January 1, 2009 to September 30, 2020. Author, title, source, year of publication, and DOI were exported via Web of Science. This initial search for literature yielded 2,440 papers. 

Initial Filtering of Journal Articles

During the initial round of examining articles, only the titles and the abstracts were analyzed. In a datasheet, articles were kept if there was evidence of 1) “plant growth-promoting rhizobacteria (PGPR),” 2) rhizobia and legume species, and 3) “nodule/nodulation” within the abstract. All other articles were removed from further cataloging.

Phenotype Coding

Articles were accessed using Chapman University Leatherby Library. Articles were examined for legume and rhizobia species and phenotypes. 25 phenotypes were identified: “Rhizobia Growth or Growth Rate,”  “Plant Growth or Dry Weight or Fresh Weight, “Root Dry Weight or Density,” “Root Branching or Length,” Rhizobia Colony Morphology,” “Rhizobia Number,” “Shoot Dry Weight,” “Nodule Dry Weight,” “Number of Nodules Per Plant,” “Number of Nodules,” “Acetylene Reduction,” “Isotopic 15N,” “Biomass,” “Chlorophyll,” “Roots Per Plant,” “Leaf Number or Weight,” “Shoot Length,” “Nitrogen Fixation,” “Nodule Occupancy or Diversity,” “Seed Count or Production,” “Nodule Structure,” “Shoot Number,” “Root/Shoot Ratio,” “Branch Dry Weight,” and “Nodule Color.” Phenotype categories were added throughout the process of reading articles if necessary. Phenotypes that were present in journal articles were marked with a ‘Y’ on the datasheet. A total of 771 articles were analyzed for phenotypes.