In particular, this screen revealed that Rm41 was unable to nodulate the plant genotypes F83005.5 and Turkey (Figure 1), while the same plant genotypes nodulated nor- mally with other S. meliloti strains. Thus, we postulate that there exist host genes that control strain-specific nodula- tion in M. truncatula. For genetic analysis of the nodula- tion specificity in this system, we chose to focus on F83005.5 because Turkey was not compatible when crossed with several other M. truncatula genotypes.