The genic-cytoplasmic male sterility presently used, worldwide, in onion for commerdal exploitation of heterosis was originally derived from var.
Italian Red 13–53 by Jones and Emsweller (1937). The second source of CMS (T-cytoplasm) in onion was discovered by Berninger (1965) in the Frendh cultivar 'Jaune paille des venus'. This CMS line was found to be different than Jones' s line, as three independent segregating restorer lod were identified in this line leading to its complex inheritance, besides this, it has common occurrence of restorers, which makes this T-cytoplasm more difficult to use.
Apart from these, male sterility has been observed in several other onion populations, mainly in long day cultivars, e.g. 'Pukekohe Longkeeper', 'Red Wethersfield', 'Scott County Globe', 'Stuttgarter Riesen' and 'Zittauer Glebe'. These have not been characterized and their relationship to S or T-cytoplasm needs to be established.
The use of single CMS source by onion hybrid industry, derived from 'Italian Red 13–53' has raised concerns regarding genetic vulnerability.
There are also reports which indicate the influence of environmental factors on this male sterility, leading to occasional fertile plants in the population.
Thus the need for another source of male sterility (CMS) is well emphasized.
During the heterosis breeding program of onion, at the Indian Institute of Horticultural Research, Bangalore, India, male sterility was located in a local cultivar 'Nasik White Globe'. The male sterile plants had anthers with translucent, green appearance in contrast to dark green normal anthers.
The meiosis was normal and degeneration of microspores started after tetrad stage, which finally lead to complete pollen sterility.
To identify maintainer lines, the male sterile plants were crossed initially with about 50 indigenous accessions.
All the F1 hybrids thus produced were male sterile, indicating widespread distribution of 'ms' genes in the population.
Subsequently during further studies, more than 350 accessions including both exotic and indigenous lines were crossed with the male sterile plants.
This time again all the F1 plants, in all the crosses were male sterile.
Among the exotic lines used in this study, some of them supposedly had 'Ms' gene widespread in their populations.
However, probably the 'Ms' gene was not able to express itself in the new cytoplasmic background.
This indicates the possibility of strong cytoplasmic factor(s) controlling the male sterility in this case.
This line is also stable for it's male sterility trait as it did not get affected by the prevailing temperature fluctuations at Bangalore.
This male sterility has been successfully used in the heterosis breeding program, which as lead to the development of two hybrids viz.
Hybrid-1 and Hybrid-5 which are ready for commercial release.