RESPONSE TO SELECTION ON AUTOGAMY IN PHLOX

Two cycles of artificial selection were performed to increase autogamo us fruiting in two wild populations of the self-incompatible Phlox dru mmondii, to decrease autogamous fruiting in two wild populations of th e self-compatible Phlox cuspidata, and to both increase and decrease a utogamous fruiting in a cultivar of P. drummondii which is pseudo-self -compatible. The breeding systems were determined to be genetically qu ite flexible, independent of inbreeding depression and other genetic p henomena which could hinder a breeding system shift. This is especiall y true for increasing autogamy. Self-pollen-pistil compatibility seems to be the single character affected by selection. Based on the contin uous variation in both autogamy and self-compatibility, we suggest tha t the change has been due to genes which modify the self-incompatibili ty reaction rather than to the simple segregation of alleles at the S- locus.