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Submitted to: Journal of Nematology
Publication Type: Abstract Only Publication Acceptance Date: 7/12/2010 Publication Date: 9/15/2010 Citation: Timper, P. 2010. AN 11-YEAR FIELD STUDY WITH PASTEURIA PENETRANS: LESSONS LEARNED THE HARD WAY.. Journal of Nematology. 42:274. Interpretive Summary: Technical Abstract: Beginning in 1998, a bioassay using second-stage juveniles (J2) from a greenhouse (GH) population of the root-knot nematode Meloidogyne arenaria (Ma) was used to monitor endospore densities of the bacterium Pasteuria penetrans, which was parasitizing Ma in a long-term rotation study (begun in 1991). Spore densities of the bacterium were very high in continuous peanuts (21 attached spores/GH J2) and very low when peanut was rotated with non-hosts for Ma (0.5 spores/GH J2). Lesson 1: even the most straightforward studies do not always turn out as planned. In 2000, the rotation sequences were changed to include additional hosts for the nematode. Based on previous studies, spore densities of P. penetrans were expected to increase rapidly (<4 years) where hosts for the nematode were frequently planted. However, spore densities did not increase after 8 years in continuous peanut (0.3 spores/GH J2). Lesson 2: do not underestimate the genetic diversity of root-knot nematodes and P. penetrans. To determine the susceptibility of Ma to P. penetrans, five single egg-mass (SEM) lines from the field population of the nematode were compared to the GH population for acquisition of endospores from the field soil. Four of the five SEM lines acquired 9 to 14 spores/J2; whereas, the GH population and one of the SEM lines acquired 3.5 and 1.8 spores/J2, respectively. These results indicate that the field population of Ma is heterogeneous for attachment of P. penetrans spores. Lesson 3: do not rely exclusively on a bioassay to determine abundance of P. penetrans. Had native J2 in the soil been examined, an increase in spore attachment over time may have been observed. In 2008, spore densities estimated with the four receptive SEM lines were highest in plots with continuous peanut (14-20 spores/J2), intermediate with two consecutive hosts (6-7 spores/J2), and lowest with only one host in a 3-year rotation (<1 spore/J2). Therefore, spore densities had increased under intensive cropping of hosts for Ma, but the GH population of the nematode was not receptive to spore attachment. However, previously, the GH population was very receptive to spore acquisition from this field site. One explanation for this inconsistency is that 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. |
