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

Summary The 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 (N e ), rather than the real numbers of individuals in the population (N). The objectives of the present study were to estimate N e in the potato cyst nematode Globodera pallida using artificial populations and to explore the link between N e and the durability of plant resistances. Using a temporal method on 24 independent pairs of initial and final populations, the median N e was 58 individuals. N e is commonly lower than N but in our case the N e /N ratio was extremely low because G. pallida populations 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 N e could be important for the control of phytoparasitic nematodes because G. pallida populations 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.