Twenty-one new sources of CMS were produced using interspecific hybridization, experimental mutagenesis and spontaneous expression of male sterility in sunflower. For all CMS sources, fertility restorers have been discovered.

All CMS are a result of cytoplasmic mutation. It is theorized that transformation of the mitochondrial genes controlling the pollen production is envoked by the influence of a single command from the cell nucleus to the mitochondria. The transformation appears to be irreversable. Commands for pollen production could be only accepted by the mitochondrial genes in case of existence of a fertility restoring gene in the cell nucleus of sterile cytoplasm