Molecular Marker Characterization of Commercially Used Cytoplasmic Male Sterilities in Onion

A BSTRACT . Hybrid-onion ( Allium cepa ) seed is produced using systems of cytoplasmic male sterility (CMS) and two different CMS systems have been genetically characterized. S cytoplasm was the fi rst source of onion CMS identi fi ed in the 1920s, followed by T cytoplasm that was described in the 1960s. Numerous studies have documented polymor- phisms in the organellar DNAs differentiating S and T cytoplasms from the normal male-fertile cytoplasm of onion. There may be additional source(s) of onion CMS that have been described as “ T-like ” and appear to be more similar to N and T cytoplasms than S cytoplasm. In this study, onion breeding lines from commercial entities were evaluated for molecular markers distinguishing sources of onion CMS. Our results reveal that bona fi de T cytoplasm is rarely used commercially to produce hybrid-onion seed, and both S cytoplasm and “ T-like ” cytoplasm are widely used. We propose that this “ T-like ” cytoplasm be labeled as “ R ” cytoplasm because it may have originated from population(s) of ‘ Rijnsburger ’ onion in the Netherlands. The results of this study also help to clarify inconsistent reports regarding nuclear male-fertility restoration for different sources of onion CMS.