Human selection and the relaxation of legume defences against ineffective rhizobia

E. Toby Kiers, Mark G. Hutton, R. Ford Denison

Research output: Contribution to journalArticlepeer-review

123 Scopus citations


Enforcement mechanisms are thought to be important in maintaining mutualistic cooperation between species. A clear example of an enforcement mechanism is how legumes impose sanctions on rhizobial symbionts that fail to provide sufficient fixed N2. However, with domestication and breeding in high-soil-N environments, humans may have altered these natural legume defences and reduced the agricultural benefits of the symbiosis. Using six genotypes of soya beans, representing 60 years of breeding, we show that, as a group, older cultivars were better able to maintain fitness than newer cultivars (seed production) when infected with a mixture of effective and ineffective rhizobial strains. Additionally, we found small differences among cultivars in the ratio of effective : ineffective rhizobia released from their nodules, an indicator of future rhizobial strain fitness. When infected by symbionts varying in quality, legume defences against poor-quality partners have apparently worsened under decades of artificial selection.

Original languageEnglish (US)
Pages (from-to)3119-3126
Number of pages8
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1629
StatePublished - Dec 22 2007

Bibliographical note

Copyright 2017 Elsevier B.V., All rights reserved.


  • Cheat
  • Mutualism
  • Nitrogen fixation
  • Partner choice
  • Punish
  • Sanction


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