Male sterility and somatic hybridization in plant breeding

Abstract

Plant male sterility refers to the failure in the production of fertile pollen. It occurs spon-taneously in natural populations and may be caused by genes encoded in the nuclear (genicmale sterility; GMS) or mitochondrial (cytoplasmic male sterility; CMS) genomes. Thisfeature has great agronomic value for the production of hybrid seeds, since it prevents self-pollination without the need of emasculation which is time-consuming and cost-intensive.CMS has been widely used in crops, such as corn, rice, wheat, citrus, and several speciesof the family Solanaceae. Mitochondrial genes determining CMS have been uncovered ina wide range of plant species. The modes of action of CMS have been classified in terms ofthe effect they produce in the cell, which ultimately leads to a failure in the production offertile pollen. Male fertility can be restored by nuclear-encoded genes, termed restorer-of-fertility (Rf) factors. CMS from wild plants has been transferred to species of agronomicinterest through somatic hybridization. Somatic hybrids have also been produced togenerate CMS de novo upon recombination of the mitochondrial genomes of two parentalplants or by separating the CMS cytoplasm from the nuclear Rf alleles. As a result, somatichybridization can be used as a highly efficient and useful strategy to incorporate CMS inbreeding programs.