Mapping of rice Ur1 (Undulated rachis-1) gene with effect on increasing spikelet number per panicle and sink size, and development of selection markers for the breeding by the use of Ur1

Ur1 enhances secondary rachis-branching, resulting in more spikelets per panicle. This genic effect can increase grain yield by enlarging sink size. We conducted mapping of Ur1 using SSR markers, and detected markers usable for the MAS (marker-assisted selection) for Ur1. Three Ur1 isogenic lines of recurrent parents Taichung 65, 'Shiokari' and 'Nishihikari'('T-U', 'S-U' and 'N-U', respectively) were used. SSR-marker analysis indicated that each isogenic line had a non-substituted region containing Ur1 on chromosome 6 which was inherited from its donor parent. T-U was crossed with a non-Ur1-carrying line, and the F-2 and F-3 populations were grown. Recombination values between the Ur1 locus and SSR-marker loci were obtained from data of the F-2 and F-3. On the basis of both the linkage relationship and the non-substituted regions in T-U, S-U and N-U, candidate region of the Ur1 locus was narrowed to 0.139 Mb between the loci of up85938 and SSR17 on the long arm of chromosome 6. Genotypes of T-U and other five Ur1-carrying lines at each locus of ten SSR markers near the Ur1 locus were determined, and allelic frequency at each locus was investigated for 27 japonica and 21 indica varieties. Consequently, SSR12 and SSR17 could be employed as MAS markers for Ur1.