Polymorphisms for Defence and Virulence in the Arabidopsis thaliana–Cucumber mosaic virus Interaction Are Expressed in the Host’s Native Habitat

Plant defences are assumed to evolve in response to the negative effects of virus infection on plant fitness (virulence), and to drive plant–virus coevolution. However, viruses are not always antagonistic symbionts of plants, and the expression of defence traits is environment-dependent. Thus, understanding plant–virus interactions requires analysing the expression of defence traits in the host’s native habitat. Here we analyse the effect of cucumber mosaic virus (CMV) infection, and the expression of resistance and tolerance in the native habitat of a wild Arabidopsis thaliana population. Plants from ten genotypes from that population, which have been shown to differ in resistance and tolerance to CMV in a greenhouse, were inoculated with an Arabidopsis isolate of CMV and transplanted to their habitat. Resistance was rated based on virus accumulation in leaves, and tolerance was rated based on the effect of infection on plant fecundity relative to virus accumulation. Consistent with the greenhouse assays, virulence depended on the host genotype, and polymorphisms for resistance and tolerance were expressed in the field, supporting the validity of the conclusions from the greenhouse assays. Our results also support theoretical predictions on the relationships between pathogen multiplication and virulence and between resistance and tolerance.