Journal of Integrative Plant Biology 2006, 48 (3): 341-347 Received 18 Aug. 2005 Accepted 5 Oct. 2005 Supported by the Hi-Tech Research and Development (863) Program of China (2002AA221003) and the National Natural Science Foundation of China (30425034). *Author for correspondence. Tel: +86 (0)571 6337 0537; Fax: +86 (0)571 6337 0389; E-mail: <qianqian188@hotmail.com>. www.blackwell-synergy.com; www.chineseplantscience.com Genetic Analysis and Gene-Mapping of Two Reduced- Culm-Number Mutants in Rice Hua Jiang 1, 2 , Long-Biao Guo 1 , Da-Wei Xue 1 , Da-Li Zeng 1 , Guang-Heng Zhang 1 , Guo-Jun Dong 1 , Ming-Hong Gu 2 and Qian Qian 1* (1. State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou 310006, China; 2. Agricultural College, Yangzhou University, Yangzhou 225006, China) Abstract In the present study, in order to systematically dissect the genetic mechanism of rice (Oryza sativa L.) tilling for the super rice ideotype and the model system of branching development, two ethyl methane sulfonate-induced rice reduced-culm-number (rcn) mutants from the progeny of Nippobare (O. sativa ssp. japonica), namely rcn8 and rcn9, were used. Their maximum tillers were both less than 4. In addition, rcn9 had another major feature of rust-spotted leaves. Allelic tests between these two mutants and seven other recessive few-tiller mutants revealed that they were previously unknown loci. Genetic analysis showed that the rcn traits were all controlled by a pair of different recessive genes, designated as RCN8 and RCN9, respectively. Two F 2 populations derived from crosses between the rcn8 or rcn9 mutants and 93-11 were constructed. Linkage analysis using two rcn F 2 mapping populations with published simple sequence repeat markers demonstrated that the RCN8 and RCN9 genes were mapped on the long arm of chromosome 1 (119.6 cM) and the short arm of chromosome 6 (63.6 cM), respectively. The results of the present study are beneficial to map-based cloning and functional analysis of the RCN8 and RCN9 genes. Key words: gene-mapping; reduced-culm-number; rice; simple sequence repeat marker. Jiang H, Guo LB, Xue DW, Zeng DL, Zhang GH, Dong GJ, Gu MH, Qian Q (2006). Genetic analysis and gene-mapping of two reduced-culm-number mutants in rice. J Integrat Plant Biol 48(3), 341-347. Tillering in rice (Oryza sativa L.) is one of the most important agronomic traits for grain production and has a facility for accu- mulation of information in terms of developmental biology for the study of branching in monocotyledonous plants (Li et al. 2003a). Many studies have found that the tiller number is widely controlled by quantitative trait loci (QTL). Xiong (1992) reported that tillers per plant held a relatively low heritability of 29.8%–49.6%. Using traditional genetic analysis, Li et al. (1997), Murai and Kinosita (1986), and Ahmad et al. (1986) reported that final tillers per plant were controlled by multigenes with different additive, dominant, and epistatic effects. Xu and Shenm (1991) showed that the additive effects for controlling tiller number with the growth of rice plants increased gradually, but non-additive effects and en- vironmental factors decreased. Using molecular genetic analysis, many QTLs for final tiller number have been identified on 10 rice chromosomes, except on chromosomes 9 and 10 (Yan et al. 1998; Xing et al. 2002). Yan et al. (1998) found that the number of QTL significantly affecting tiller number was different at different growth stages. However, some researchers have confirmed that the tiller number in rice can be controlled by one single gene. Tang et al. (2001) reported on a mutant, namely G069, with few tiller numbers controlled by one recessive gene FEW-TILLING 1 (FT1). The FT1 gene was mapped to chromosome 2 between restriction fragment length polymorphism (RFLP) markers C424 and S13984. Li et al. (2003a) screened a spontaneous monoculm 1 (moc1) mutant and isolated and characterized the MOC1 gene encoding a putative GRAS (GAI (GIBBERELLIN-INSENSITIVE), RGA (REPRESSOR of ga1–3), SCR(SCARECROW)) family nuclear protein. However, in the rice genome, there are approximately 50 000–60 000 genes (Goff et al. 2002), and less than 30% of them