Evidence for Reciprocal Selection between Populations of Meloidogyne arenaria and Pasteuria penetrans in a Field Study

Authors: Timper, Patricia - Patty

Submitted to: European Society of Nematologists
Publication Type: Abstract Only
Publication Acceptance Date: 9/19/2010
Publication Date: 9/19/2010
Citation: Timper, P. 2010. Evidence for Reciprocal Selection between Populations of Meloidogyne arenaria and Pasteuria penetrans in a Field Study [abstract]. 30th International Symposium of the European Society of Nematologists. pg. 35.

Interpretive Summary: Beginning in 1998, a bioassay using second-stage juveniles (J2) from a greenhouse (GH) population of Meloidogyne arenaria (Ma) was used to monitor endospore densities of the bacterium Pasteuria penetrans, which was parasitizing Ma in a crop rotation study. Spore densities of the bacterium were very high in plots where hosts for the nematode were frequently grown (21 spores/GH J2). In 2000 and 2001, the spore levels declined and then remained low (< 2 spores/GH J2) until the fall of 2008 when levels increased to 4 spores/GH J2). To determine the susceptibility of Ma to P. penetrans, five single egg-mass (SEM) lines from the field population of Ma were tested alongside the GH population for acquisition of spores from the field soil. Four of the five SEM lines acquired 17 spores/J2; whereas, the GH population and one SEM line acquired 4 and 3 spores/J2, respectively. This indicates that the field population of Ma is heterogeneous for attachment of P. penetrans spores. The change in susceptibility of the GH population can be explained by reciprocal selection, in which the Ma population in the field became resistant to the dominant subpopulation of P. penetrans that had been present and this led to the selection of a different subpopulation of the bacterium (now dominant in the field) that is incompatible with the GH population.

Technical Abstract: Beginning in 1998, a bioassay using second-stage juveniles (J2) from a greenhouse (GH) population of Meloidogyne arenaria (Ma) was used to monitor endospore densities of the bacterium Pasteuria penetrans, which was parasitizing Ma in a crop rotation study. Spore densities of the bacterium were very high in plots where hosts for the nematode were frequently grown (21 spores/GH J2). In 2000 and 2001, the spore levels declined and then remained low (< 2 spores/GH J2) until the fall of 2008 when levels increased to 4 spores/GH J2). To determine the susceptibility of Ma to P. penetrans, five single egg-mass (SEM) lines from the field population of Ma were tested alongside the GH population for acquisition of spores from the field soil. Four of the five SEM lines acquired 17 spores/J2; whereas, the GH population and one SEM line acquired 4 and 3 spores/J2, respectively. This indicates that the field population of Ma is heterogeneous for attachment of P. penetrans spores. The change in susceptibility of the GH population can be explained by reciprocal selection, in which the Ma population in the field became resistant to the dominant subpopulation of P. penetrans that had been present and this led to the selection of a different subpopulation of the bacterium (now dominant in the field) that is incompatible with the GH population.