Variation of inbreeding depression in Centaurea cyanus L., a self-incompatible species

The evolutionary trajectory of isolated or small populations of self-incompatible species depends on genetic variation in the capacity to transition to self-compatibility and the impact of inbreeding on plant fitness. Centaurea cyanus is an example of a self-incompatible, arable field-dependent weed species that is in regression in western Europe due to agricultural intensification. However, some cases of self-fertilization have been observed. Here, we investigated how inbreeding depression impacts the plants by studying two generations of self-fertilized families. As early as at the stage of the first selfing generation, we observed reduction in the number of florets per capitulum. By the second selfing generation, we observed reductions in germination rate, plant height, above-ground plant biomass, seed set and the final number and mass of seeds per plant. In particular, dramatically lower germination rate and reduced seed set contributed to a low cumulative fitness index of the generations that resulted from selfing. Nevertheless, although high average inbreeding depression was observed, large variation in cumulative fitness among families would allow some of these selfed families to persist and trigger evolution of selfing in small, isolated populations.