Polyploidy is frequently associated with plant speciation and domestication.Indeed,shifts in ploidy can result in reproductive isolation via postzygotic lethality and permit divergence of the two isolated populations.Using Arabidopsis thaliana natural variation and genomic resources we have determined the genetic basis of variation in interploidy crossing success.Remarkably,polyploid derivatives of different ecotypes of A.thaliana vary many-fold in their degree of reproductive isolation from diploids.Dissection of the genetic architecture of this variability via QTL analyses has identified both maternally and paternally derived genetic controls.