UNILATERAL INCOMPATIBILITY AND THE EFFECTS OF INTERSPECIFIC POLLINATION FOR ERYTHRONIUM-AMERICANUM AND ERYTHRONIUM-ALBIDUM (LILIACEAE)

To determine whether interspecific pollen transfer could reduce seed p roduction by two sympatric lilies, Erythronium albidum and Erythronium americanum, we hand-pollinated flowers with mixtures of conspecific a nd heterospecific pollen. These species exhibited typical unilateral i nterspecific incompatibility, i.e., pollen tubes from the self-inferti le species (E. americanum) grew apparently unimpeded in styles of the self-fertile species (E. albidum), whereas the reverse cross resulted in an incompatibility reaction. Because of this asymmetrical relation and faster growth by heterospecific pollen tubes in E. albidum stigmas than by conspecific tubes, pollination with abundant heterospecific p ollen reduced fruit and seed production by E. albidum, but not by E. a mericanum, as long as the stigma also received some conspecific pollen . Unilateral incompatibility could benefit self-infertile species in r eproductive interactions with closely related self-fertile species; ho wever, this benefit remains to be demonstrated for naturally pollinate d plants.