Population dynamics of Meloidogyne arenaria and Pasteuria penetrans in a long-term crop rotation study.

Authors: Timper, Patricia - Patty

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2010
Publication Date: 12/24/2009
Citation: Timper, P. 2009. Population dynamics of Meloidogyne arenaria and Pasteuria penetrans in a long-term crop rotation study. Journal of Nematology. 41:291-299.

Interpretive Summary: Root-knot nematodes cause damage to a wide variety of crop plants. The bacterium Pasteuria penetrans is an obligate parasite of these nematodes. This study was a continuation of earlier research to determine the effect of crop sequence on abundance of the bacterium, and was conducted from 2000 to 2008 at a field site naturally infested with both Pasteuria and the peanut root-knot nematode (PRKN). The experiment included the following crop sequences: continuous peanut (P-P-P) and peanut rotated with either 2 years of corn (C-C-P), 1 year each of cotton and corn (Ct-C-P), or 1 year each of corn and a vegetable (V-C-P). The vegetable was a double crop of sweet corn and eggplant. A bioassay with second-stage juveniles (J2) of PRKN from a greenhouse culture was used to estimate abundance of Pasteuria spores under the different crop sequences. I hypothesized that the P-P-P and V-C-P sequences would lead to a greater numerical increase in Pasteuria densities than the other rotations because both peanut and eggplant are good hosts for PRKN. Pasteuria densities, however, failed to substantially increase in any of the sequences during the 9-year experiment. Five single egg-mass colonies were established from the field population of PRKN and tested alongside the greenhouse culture for acquisition of Pasteuria spores from five areas of the field. Four of the five colonies acquired 9 to 14 spores/J2; whereas, the greenhouse culture and the C6 colony acquired 3.5 and 1.8 spores/J2, respectively. Spore densities estimated with the four receptive colonies were highest in the P-P-P plots (14-20 spores/J2), intermediate in the V-C-P plots (6-7 spores/J2), and lowest in the Ct-C-P plots (<1 spore/J2). These results indicate that the field population of PRKN is heterogeneous for attachment of Pasteuria spores. Moreover, spore densities had increased under intensive cropping of hosts for PRKN, but the greenhouse culture of the nematode was not receptive to spore attachment. However, previously, the greenhouse culture was very receptive to spore acquisition from this field site. One explanation for this inconsistency is that the PRKN population in the field became resistant to the dominant subpopulation of Pasteuria that had been present and this led to selection of a different subpopulation of the bacterium that is incompatible with the greenhouse culture.

Technical Abstract: The endospore-forming bacterium Pasteuria penetrans is an obligate parasite of root-knot nematodes (Meloidogyne spp.). This study was a continuation of earlier research to determine the effect of crop sequence on abundance of the bacterium, and was conducted from 2000 to 2008 at a field site naturally infested with both P. penetrans and its host Meloidogyne arenaria. The experiment included the following crop sequences: continuous peanut (Arachis hypogaea) (P-P-P) and peanut rotated with either 2 years of corn (Zea mays) (C-C-P), 1 year each of cotton (Gossypium hirsutum) and corn (Ct-C-P), or 1 year each of corn and a vegetable (V-C-P). The vegetable was a double crop of sweet corn and eggplant (Solanum melongena). A bioassay with second-stage juveniles (J2) of M. arenaria from a greenhouse culture was used to estimate endospore abundance under the different crop sequences. I hypothesized that the P-P-P and V-C-P sequences would lead to a greater numerical increase in endospore densities than the other rotations because both peanut and eggplant are good hosts for M. arenaria. Endospore densities, however, failed to substantially increase in any of the sequences during the 9-year experiment. Five single egg-mass colonies were established from the field population of M. arenaria and tested alongside the greenhouse culture for acquisition of endospores from five areas of the field. Four of the five colonies acquired 9 to 14 spores/J2; whereas, the greenhouse culture and the C6 colony acquired 3.5 and 1.8 spores/J2, respectively. Endospore densities estimated with the four receptive colonies were highest in the P-P-P plots (14-20 spores/J2), intermediate in the V-C-P plots (6-7 spores/J2), and lowest in the Ct-C-P plots (<1 spore/J2). These results indicate that the field population of M. arenaria is heterogeneous for attachment of P. penetrans spores. Moreover, spore densities had increased under intensive cropping of hosts for M. arenaria, but the greenhouse culture of the nematode was not receptive to spore attachment. However, previously, the greenhouse culture was very receptive to spore acquisition from this field site. One explanation for this inconsistency is that the M. arenaria population in the field became resistant to the dominant subpopulation of P. penetrans that had been present and this led to selection of a different subpopulation of the bacterium that is incompatible with the greenhouse culture.