ture of female line seed in the hybrid seed results in yield reduction of 100 kg per hectare (Mao et al., 1996). Ensuring the genetic purity of parental lines and hybrids is a prereq-The Indian seed act prescribes that, for hybrid rice, uisite to realize their full potential. The cytoplasmic male sterile (CMS) the purity should be 98% (Verma, 1996), while in the lines that are utilized for developing the popular "three-line" hybrids, often get contaminated with their isonuclear maintainer lines during