Effects of cytoplasm and cytoplasm-nucleus interaction in breeding japonica rice
2003
Tao, D. | Hu, F. | Yang, G. | Yang, J. | Xu, P. | Li, J. | Ye, C. | Dai, L.
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, Lijiangxintuanheigu, and Norinmoti No.20. Then, seven backcrosses using the male parent as the recurrent parent were made. Fifteen crosses of BC7F2 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°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 studies, 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 future rice breeding, the role of cytoplasm and cytoplasm-nucleus interaction should be given more attention.
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