Effective population size and durability of plant resistances in the potato cyst nematode Globodera pallida

SummaryThe effective size of a population is the size of an ideal population which would drift at the same rate as the real population. The balance between selection and genetic drift depends on the population size expressed as the genetically effective population size (Ne), rather than the real numbers of individuals in the population (N).The objectives of the present study were to estimate Nein the potato cyst nematodeGlobodera pallidausing artificial populations and to explore the link between Neand the durability of plant resistances.Using a temporal method on 24 independent pairs of initial and final populations, the median Newas 58 individuals.Neis commonly lower than N but in our case the Ne/N ratio was extremely low becauseG. pallidapopulations deviate in structure from the assumptions of the ideal population by having unequal sex-ratios, high levels of inbreeding and a high variance in family sizes. The consequences of a low Necould be important for the control of phytoparasitic nematodes becauseG. pallidapopulations will have a low capacity to adapt to changing environments unless selection intensity is very strong, which could be greatly beneficial for long-term use of plant resistances.