title: Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 1. Insights from the estimation of effective population sizes.
abstract: The sustainability of modern agriculture relies on strategies that can control the ability of pathogens to overcome chemicals or genetic resistances through natural selection. This evolutionary potential, which depends partly on effective population size (N e ), is greatly influenced by human activities. In this context, wild pathogen populations can provide valuable information for assessing the long-term risk associated with crop pests. In this study, we estimated the effective population size of the beet cyst nematode, Heterodera schachtii, by sampling 34 populations infecting the sea beet Beta vulgaris spp. maritima twice within a one-year period. Only 20 populations produced enough generations to analyze the variation in allele frequencies, with the remaining populations showing a high mortality rate of the host plant after only 1 year. The 20 analyzed populations showed surprisingly low effective population sizes, with most having N e close to 85 individuals. We attribute these low values to the variation in population size through time, systematic inbreeding, and unbalanced sex-ratios. Our results suggest that H. schachtii has low evolutionary potential in natural environments. Pest control strategies in which populations on crops mimic wild populations may help prevent parasite adaptation to host resistance.
authors.affiliation: INRA UMR1349 IGEPPF-35653 Le Rheu Cedex France; INRA UMR985 ESEF-35042 Rennes Cedex France.
authors.forename: Pierre-Loup
authors.initials: PL
authors.lastname: Jan
authors.affiliation: INRA UMR1349 IGEPP F-35653 Le Rheu Cedex France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Gracianne
authors.affiliation: INRA UMR1349 IGEPP F-35653 Le Rheu Cedex France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Fournet
authors.affiliation: INRA UMR1349 IGEPP F-35653 Le Rheu Cedex France.
authors.forename: Eric
authors.initials: E
authors.lastname: Olivier
authors.affiliation: UMR CNRS 8198 Évolution, Écologie et Paléontologie Université Lille 1 - Sciences et Technologies 59655 Villeneuve d'Ascq Cedex France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Arnaud
authors.affiliation: INRA UMR1349 IGEPP F-35653 Le Rheu Cedex France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Porte
authors.affiliation: INRA UMR1349 IGEPP F-35653 Le Rheu Cedex France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Bardou-Valette
authors.affiliation: INRA UMR1349 IGEPP F-35653 Le Rheu Cedex France.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Denis
authors.affiliation: INRA UMR985 ESE F-35042 Rennes Cedex France.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Petit
keywords: Beta vulgaris spp. maritima; Heterodera schachtii; effective population size; temporal sampling; wild nematode populations