The present invention relates to a novel cytoplasmic male sterility (CMS) `126-1` system in different Brassica species and a method for obtaining male sterile lines using the said CMS. The CMS has distinct mitochondrial DNA specific RFLP signature. The invention also relates to a method for obtaining male sterile lines and restoration of fertility in B. juncea for hybrid seed production. This CMS in B. juncea can be restored by crossing male sterile plants with any B. juncea genotype other than the maintainer genotype. The same B. juncea genotype acts as maintainer of male sterility after a specified number of backcrosses. This invention also relates to the histological characterization of anther and microspore development in B. juncea.