Reproductive isolation on interspecific backcross of F1 pollen to parental species, <Emphasis Type="Italic">Hemerocallis fulva</Emphasis> and <Emphasis Type="Italic">H. citrina</Emphasis> (Hemerocallidaceae)

Reproductive failure of backcross could play important roles in determining the evolutionary outcome of hybridization. However, such studies have been somewhat fewer than those of the F1-producing cross and F1 × F1 cross. We conducted hand-pollination backcross experiments using Hemerocallis fulva, H. citrina, and their F1 hybrids. Seed set per flower of the backcrosses reduced to about 50% of the control cross, irrespective of ovule parent species. This symmetrical seed set reduction on the backcross might be caused by the death of backcross embryo as a result of Dobzhansky–Muller incompatibility by recessive alleles.