9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Self-incompatibility refers to the genetic inability of fully functional pollen grains and ovules to produce viable seeds. This is mainly due to the presence of S or self genes. If these genes are present in pollen as well as ovule, they will not be able to produce viable seeds. Self-pollination does not lead to the formation of seeds in self-incompatible species due to the presence of certain chemical substances that block the germination of pollen grains on stigma and also obstruct their passage to the ovary.