PLANT-MYCORRHIZAL FUNGUS INTERACTIONS AFFECT THE EXPRESSION OF INBREEDING DEPRESSION IN WILD STRAWBERRY

The influence of biotic interactions on the expression of inbreeding depression has received only modest investigation; however, these interactions may be important in determining the magnitude and/or variation of inbreeding depression seen in the wild and invoked in models of mating and sexual system evolution. We present the first experimental test of the effects of plant-mycorrhizal fungus interactions on the expression of inbreeding depression. We inoculated selfed and outcrossed seedlings from eight hermaphrodite genotypes of wild strawberry (Fragaria virginiana) with mycorrhizal fungal spores and determined the effect on vegetative growth and sexual and asexual reproduction. We found that inoculated plants grew at rates similar to those of control plants but produced fewer flowers and more plantlets than controls. However, some of these effects varied with maternal genotype and cross type. As a consequence, mycorrhizal fungal inoculation had variable and trait-dependent effects on the expression of inbreeding depression. We discuss the results in light of the conditional nature of plant-mycorrhiza associations and in light of their potential to influence mating and sexual system evolution.