Competitive Index: Mixed Infection-Based Virulence Assays for Genetic Analysis in Pseudomonas syringae-Plant Interactions

  • Alberto P. Macho
  • José S. Rufián
  • Javier Ruiz-Albert
  • Carmen R. BeuzónEmail author
Part of the Methods in Molecular Biology book series (MIMB, volume 1363)


When studying bacterial plant pathogens, the genetic analysis of the contribution of virulence factors to the infection process has traditionally been hindered by their high degree of functional redundancy. In recent years, it has become clear that the use of competitive index in mixed infections provides an accurate and sensitive manner of establishing virulence phenotypes for mutants for which other assays have failed. Such increases in sensitivity and accuracy are due to the direct comparison between the respective growths of the co-inoculated strains within the same infection, each strain replicating as they would in individual infections. Interferences between the co-inoculated strains must be therefore avoided using the appropriate experimental settings. In this chapter, we will present the optimal experimental conditions to achieve maximum sensitivity on virulence assays using the phytopathogenic bacterium Pseudomonas syringae, as well as some additional considerations to ensure the correct interpretations of the results.

Key words

Mixed infection Competitive index Virulence Immunity Resistance Genetic analysis 



The work was supported by Project Grants from the Ministerio de Economia y Competitividad (MINECO, Spain; BIO2012-35641) and Junta de Andalucía (Spain; P07-CVI-2605) to C.R. Beuzón. J.S. Rufián is currently supported by a FPI fellowship to a Project Grant to E.R. Bejarano (MICINN, Spain; AGL2010-22287-C02-2). The work was co-funded by Fondos Europeos de Desarrollo Regional (FEDER).


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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • Alberto P. Macho
    • 2
  • José S. Rufián
    • 1
  • Javier Ruiz-Albert
    • 1
  • Carmen R. Beuzón
    • 1
    Email author
  1. 1.Dpto. Biología Celular, Genética y Fisiología, Instituto de Hortofruticultura Subtropical y MediterráneaUniversidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC)MálagaSpain
  2. 2.Shanghai Center for Plant Stress BiologyChinese Academy of SciencesShanghaiChina

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