Science in China Series C: Life Sciences © 2007 Science in China Press Springer-Verlag www.scichina.com www.springerlink.com Sci China Ser C-Life Sci | June 2007 | vol. 50 | no. 3 | 356-366 The breeding of two polyploid rice lines with the characteristic of polyploid meiosis stability CAI DeTian 1, 2† , CHEN JianGuo 1 , CHEN DongLing 1 , DAI BingCheng 1 , ZHANG Wei 1 , SONG ZhaoJian 1 , YANG ZhiFan 1 , DU ChaoQun 1 , TANG ZhiQiang 1 , HE YuChi 1 , ZHANG DaoSheng 1 , HE GuangCun 2 & ZHU YingGuo 2 1 College of Life Science, Hubei University, Wuhan 430062, China; 2 College of Life Science, Wuhan University, Wuhan 430072, China Polyploidization is a basic feature of plant evolution. Nearly all of the main food, cotton and oil crops are polyploid. When ploidy levels increase, yields double; this phenomenon suggested a new strategy of rice breeding that utilizes wide crosses and polyploidization dual advantages to breed super rice. Because low seed set rates in polyploid rice usually makes it difficult to breed, the selection of Ph-liked gene lines was emphasized. After progenies of indica-japonica were identified and selected, two poly- ploid lines, PMeS-1 and PMeS-2 with Polyploid Meiosis Stability (PMeS) genes were bred. The proce- dure included seven steps: selecting parents, crossing or multiple crossing, back-crossing, doubling chromosomes, identifying the polyploid, and choosing plants with high seed set rates that can breed themselves into stable lines. The characteristics of PMeS were determined by observing meiotic be- haviors and by cross-identification of seed sets. PMeS-1 and PMeS-2, (japonica rice), have several characteristics different from other polyploid rice lines, including a higher rate of seed set (more than 65%, increasing to more than 70% in their F 1 offspring); and stable meiotic behaviors (pairing with bi- valents and quarivalents nearly without over-quarivalent in prophase, nearly without lagging chromo- somes in metaphase and without micronuclei in anaphase and telophase). The latter was obviously different from control polyploid line Dure-4X, which displayed abnormal meiotic behaviors including a higher rate of multivalents, univalents and trivalents in prophase, lagging chromosomes in metaphase and micronuclei in anaphase and telophase. There were also three differences of the breeding method between PMeS lines and normal diploid lines: chromosomes doubling, polyploidism identifying and higher seed set testing. The selection of PMeS lines is the first step in polyploid rice breeding; their use will advance the progress of polyploid rice breeding, which will in turn offer a new way to breed super rice. rice, polyploid, indica-joponica hybrid, polyploid meiosis stability, seed set rate Polyploidization is an important feature of plant evolu- tion [1, 2] . Recent molecular biology research indicated that nearly 100% of angiosperms of important crops such as wheat, cotton, and rape had undergone one or more polyploidization processes [3] . Moreover, their yields were doubled along with their evolution from diploid to polyploid. Accordingly, to help solve world food crises, a new strategy of utilizing the double pre- dominance of wide crosses and polyploidization to se- lect and breed super rice was explored [4] . Although a tetraploid rice was discovered by Japanese scholar Na- kamori in 1933 [5] , research on polyploid rice has pro- Received September 12, 2006; accepted November 30, 2006 doi: 10.1007/s11427-007-0049-6 † Corresponding author (email: caidt8866@yahoo.com.cn) Supported by the National Natural Science Foundation of China (Grant Nos. 39970447, 30240090, 30471063 and 30650002), the High Technology Research and Development Program of China (Grant No. SZ-01-02-02), the Chenguang Youth Science and Technology Project of Wuhan City (Grant No. 20045006071-31), and the Educational Commission of Hubei Province of China (Grant No. 2004D004)