Identification and characterization of new sources of cytoplasmic male sterility in rice

Search for male sterility-inducing cytoplasm in wild species of the genus Oryza was attempted with a view to diversify the base of the cytoplasmic genetic male sterility system currently used in the development of commercial rice hybrids. A total of 132 interspecific crosses were made involving accessions of four wild and two cultivated species, all belonging to the A genome. Wild accessions possessing sterility-inducing cytoplasms were identified following reciprocal and sterile F-2 backcross methods. Sterile segregants were pursued through substitution backcrosses to develop cytoplasmic male-sterile (CMS) lines. CMS lines were developed with the cytoplasm of either O. rufipogon (VNI) or O. nivara (DRW 21018, DRW 21001, DRW 21039, DRW 21030 and RPW 21111). Based on shape, staining, and abortive pattern of pollen and also on type of interaction with a set of restorers and maintainers for known cytoplasmic male steriles of WA source (V 20A), the newly-developed CMS lines were grouped into four classes. Of these, RPMS 1 and RPMS 2 showed gametophytic male sterility with a restorer reaction different from WA cytoplasmic male-sterile stocks.