Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 2. Separating the relative effects of gene flow and genetic drift.
Studying wild pathogen populations in natural ecosystems offers the opportunity to better understand the evolutionary dynamics of biotic diseases in crops and to enhance pest control strategies. We used simulations and genetic markers to investigate the spatial and temporal population genetic structure of wild populations of the beet cyst nematode Heterodera schachtii on a wild host plant species, the sea beet (Beta vulgaris spp. maritima), the wild ancestor of cultivated beets. Our analysis of the variation of eight microsatellite loci across four study sites showed that (i) wild H. schachtii populations displayed fine-scaled genetic structure with no evidence of substantial levels of gene flow beyond the scale of the host plant, and comparisons with simulations indicated that (ii) genetic drift substantially affected the residual signals of isolation-by-distance processes, leading to departures from migration-drift equilibrium. In contrast to what can be suspected for (crop) field populations, this showed that wild cyst nematodes have very low dispersal capabilities and are strongly disconnected from each other. Our results provide some key elements for designing pest control strategies, such as decreasing passive dispersal events to limit the spread of virulence among field nematode populations.
IGEPPINRA, Agrocampus Ouest Université Rennes 1 Le Rheu France; Vet Agro Sup, UMR 1095, GDEC Clermont Université Clermont-Ferrand France.
Cécile
C
Gracianne
IGEPPINRA, Agrocampus Ouest Université Rennes 1 Le Rheu France; ESE, Ecology and Ecosystems Health Agrocampus Ouest INRA Rennes France.
Pierre-Loup
PL
Jan
IGEPP INRA, Agrocampus Ouest Université Rennes 1 Le Rheu France.
Sylvain
S
Fournet
IGEPP INRA, Agrocampus Ouest Université Rennes 1 Le Rheu France.
Eric
E
Olivier
UMR CNRS 8198 Évolution Écologie et Paléontologie Université Lille 1 - Sciences et Technologies Villeneuve d'Ascq Cedex France.
Jean-François
JF
Arnaud
IGEPP INRA, Agrocampus Ouest Université Rennes 1 Le Rheu France.
Catherine
C
Porte
IGEPP INRA, Agrocampus Ouest Université Rennes 1 Le Rheu France.
Sylvie
S
Bardou-Valette
IGEPP INRA, Agrocampus Ouest Université Rennes 1 Le Rheu France.
Marie-Christine
MC
Denis
ESE, Ecology and Ecosystems Health Agrocampus Ouest INRA Rennes France.
Eric J
EJ
Petit
Heterodera schachtii; assignment tests; gene flow; migration–drift equilibrium; wild nematode populations