Abstract：From the composite hybrid rice (Oryza sativa L.) F2 population of breeding materials Guanghui128, japonica rice Kitaake, Shuhui955 and Shuhui881 found a mutant named TS (top-spikelet-two-grain mutant). The most significant variation of TS is the top of the first and secondary branch of spikelet of the TS, which clusters for 2~3 grains together. In order to specify the genetic mechanism of clustered gene ts and its utilization value in rice breeding, we performed morphological observation and genetic analysis of clustering traits in F1 and F2 segregating population derived from cross between TS and indica G2480B, analyzed the application prospect of ts by using 3 stable maintainer lines with ts bred by backcross and selfing for many generations. Morphological observation showed that F1 population was completely dominant and segregation ratio of F2 population fitted to a pair of gene separation mode (3∶1), which demonstrated that this trait was controlled by a single recessive gene and could stablely inherit. Gene ts was mapped onto the long arm of the Chr.6. and furtherly located between RM20323 and RM6298 according to the data from Gramene web, with genetic distance of 5.1 and 5.6 cM, respectively. L332, one of the 3 bred maintainer lines, kept clustered traits and its yield no significant differences, compared with one of the parents (G2480B), with a better cooking and eating quality. The expression of ts gene had no significant correlation with the effective panicle number, grain number per panicle, 1 000-grain weight and single plant yield of rice, and no correlation with seed setting rate. The above results provide the theoretical basic data for the use of ts gene in rice breeding.
