The production of hybrid onion (Allium cepa L.) seed is economically feasible using systems of cytoplasmic-genic male sterility(CMS). The identification of cytoplasm types might be helpful to development of sterile and maintainer lines. Due to this reason, a knowledge of the cytoplasm type is essential for hybrid breeding in onion. Especially, due to the biennial generation time of onion, to distinguish of onion cytoplasm type in individual plant may be helpful to reduce the efforts in a breeding program, when new sterile lines and the corresponding maintainer lines be developed. In our study, we applied the PCR-marker (orfA-501) to identify the cytoplasmic genotypes of collected 100 accessions of bulb onion. Among accessions, S-cytoplasm was found in 57 accessions. Nineteen accessions possessed only N-cytoplasm and twenty four accessions possessed both S- and N-cytoplasm.

Three different male-sterile cytoplasmic lines and their common maintainer 'Zhenshan 97B' and two elite restorer lines were used to study cytoplasmic effects on agronomic trait manifestation per se under different nitrogen supply levels. The result showed that cytoplasmic effects could be modified by nitrogen environments. The cytoplasmic effect on grain yield under 150 kg N/ha varied depending on crosses, while it was significantly negative in most crosses under both 60 and 330 kg N/ha. The correlation and path-coefficient analyses suggested that it was expected to improve cytoplasmic effects through reducing maximum tillers and increasing the percentage of productive tillers, leading to increased productive tillers and higher yield in hybrid rice by the aid of cultural practice and genetic transformation. This study also revealed that the same cytoplasm in different combinations had differential effect under the same nitrogen environment, indicating that cytoplasmic effect was produced by interaction of nuclear genes with cytoplasm rather than cytoplasm per se. These results indicated the usefulness of evaluating diverse cytoplasmic sources in various nuclear genotypes bred for hybrid rice breeding program. The finding also suggested that negative cytoplasmic effect could be effectively overcome by elite restorer lines through the interaction of nuclear genes with female cytoplasm.