Mapping and application of the twin-grain1 gene in rice.

The map-based cloning and application of a flower organ number gene twin - grain1 provide great potential for improving seed production in hybrid rice. A new germplasm for high-yield rice breeding, the twin-grain1 (tg1) mutant with more than one grain in a glume, was obtained from the Zhejing 22 rice variety via physical mutagenesis. The mapping results showed that TG1 is allelic to FLORAL ORGAN NUMBER2 (FON2)/FLORAL ORGAN NUMBER4 (FON4), a flower organ number gene located at 88.7 cM on chromosome 11. The novel tg1 gene allele was introgressed into the cytoplasmic male sterility (CMS) line Zhejing 22A, giving rise to a new CMS line Zhejing 22-tg1A. The Zhejing 22-tg1A line showed enhanced glume opening and stigma exsertion, which increased the outcrossing rate in hybrid rice. A small-scale hybrid rice seed production test demonstrated that the grain yield of the Zhejing 22-tg1A/Zhejinghui 5 line was significantly increased compared to that of the Zhejing 22A/Zhejinghui 5 line. The plot yield evaluation of the F hybrid lines showed a higher yield for the Zhejing 22-tg1A/Zhejinghui 5 line than that of the Zhejing 22A/Zhejinghui 5 line. The results implied great potentials for the tg1 gene in hybrid rice breeding.