Effects of cytoplasm and cytoplasm-nucleus interaction in breeding japonica rice

摘要

Long-term breeding practices indicate that some sources of cytoplasm have become more important, but the reasons for this need to be explained. Thus, five major cytoplasm sources in japonica--Xinan 175, Reimei, Keqing No. 3, Todorokiwase, and Toride No. 1--that constituted 75% of the cytoplasm of cultivars bred in Yunnan, China, were used as female parents to hybridize with three distinct japonica rice varieties--8-126, Lijiangtintuanheigu, and Norinmoti No. 20. Then, seven backcrosses using the maleparent as the recurrent parent were made. Fifteen crosses of BC_7F_2 and their parents were sown in Jinghong in the late 1999 season (July-October) for agronomic evaluation. Meanwhile, all materials were screened for low-temperature tolerance based on two methods in Kunming (1,916 m): natural field conditions and low-temperature water-cycling (19 deg C) irrigation at the booting stage. Spikelet fertility was used as an indication of low-temperature tolerance. Under the fixed model, effects of cytoplasm on yield, width and angle of flag leaf, and low-temperature tolerance were significant or very significant. Effects of cytoplasm-nucleus interaction on yield, spikelet number panicle~(-1), plant height, and low-temperature tolerance were significant. This indicated that among materials studied, genetic differences existed in japonica rice yield, low-temperature tolerance, and important agronomic traits controlled by cytoplasm and/or cytoplasm-nucleus interaction. The role of cytoplasm-nucleus interaction was significant for yield, plant height, spikelet number panicle~(-1), and spikelet fertility under natural conditions in Kunming, and for spikelet fertility under low-temperature water-cycling irrigation. The contribution of cytoplasm-nucleus interaction to these traits was 5.7%, 9.1%, 1.4%, 1.1%, and 20.6%, respectively. These results indicated that cytoplasm-nucleus interaction plays an important role in yield, low-temperature tolerance, and important agronomic traits in japonica rice. In futurerice breeding, the role of cytoplasm and cytoplasm-nucleus interaction should be given more attention.