Self-incompatibility in flowering plants is controlled by which locus?

1. Incompatibility genes prevent pollen from germinating or growing into the stigma of a flower. 2. Self-incompatibility is controlled by the S locus, where S stands for sterility. 3. In some plants, such as cabbage, pollen is rejected at the stigma surface and never germinates. 4. In others the pollen tube is arrested after growing a third of the way down the style, and then dies. 5. That death follows either programmed cell death or degradation of pollen tube RNA by a ribonuclease encoded by the same locus. 6. This mechanism matters commercially because it inhibits the production of inbred and hybrid plants. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 32 "Plant Reproduction", section 32.2 Pollination and Fertilization_