Mapping two major effect grain dormancy QTL in rice

The intrachromosomal positions of the two grain dormancy quantitative trait loci (QTL) qSdn-1 (chromosome 1) and qSdn-5 (chromosome 5) were obtained from the segregation analysis of the advanced backcross populations derived from the cross between rice (Oryza sativa L.) cultivars N22 (indica) and Nanjing35 (japonica). Marker-assisted selection (MAS) was applied to select derivatives carrying one or both of qSdn-1 and qSdn-5 in a genetic background which was nearly isogenic to Nanjing35. An analysis of dormancy in the BC4F2 population allowed qSdn-1 to be located between the simple sequence repeat (SSR) markers RM11669 and RM1216; the QTL explained 24.58% of the overall phenotypic variation and the most closely linked marker was RM11694. qSdn-5 was mapped between RM480 and RM3664, and explained 17.58% of the overall phenotypic variation. The SSR locus RM19080 mapped within 0.4 cM of qSdn-5. No epistasis was observed between qSdn-1 and qSdn-5. The mean germination rates of lines containing qSdn-1, qSdn-5 and both qSdn-1 and qSdn-5 were 7.9, 11.1 and 6.1%, respectively, whereas that of the check line lacking both QTL was 86.3%. The SSR loci linked most tightly to qSdn-1 and qSdn-5 are suitable for MAS for reduced pre-harvest sprouting in rice. The dormancy of both qSdn-1 and qSdn-5 could be readily broken by a 7-day post-harvest treatment at 50°C.