Dissecting Self-Incompatibility Although the pollen may be available for a flower to fertilize itself, molecular determinants on the pollen and the pistil prevent inbreeding in a process termed self-incompatibility. In the Petunia self-incompatibility, if male determinants (F-box proteins) on pollen are recognized by a female ribonuclease determinant on the pistil, the pollen tube is killed when its ribosomal RNA is digested. Outcrossed fertilizations can occur because of allelic diversity in the female that fails to recognize its male counterparts; however, the genetic diversity of the ribonuclease gene is greater than that of the known F-box gene. Kubo et al. (p. 796 ; see the Perspective by Indriolo and Goring ) have discovered that there are several related F-box genes in Petunia , each of which brings its own allelic diversity to bear—thus, increasing the variety of potential mating partners.