Identification of Marker Loci for Seed Dormancy in Rice (Oryza sativa L.)

Abstract

In rice breeding, genes for seed dormancy as well as the markers for each of them are required for incorporation of an adequate seed dormancy into japonica cultivars. To screen genetic loci for seed dormancy in rice (Oryza sativa L.), two kinds of populations were tested: (i) an F2 population of a hybrid Milyang 23 / Todorokiwase, and (ii) F1 populations from a three‐way cross, in which an indica donor of strong dormancy, IR 36, was crossed with non‐dormant japonica cultivars, Nekken 2 and Miyukimochi, in the form of IR 36 / Nekken 2 // Miyukimochi. The seeds produced on the F2 plants from the single cross and those on F1 plants from the three‐way cross were tested at three times: immediately after maturation, after 60 d storage at 4°C, and after breaking dormancy (7 d at 50°C). Of 24 marker loci assayed, at least four loci linked to seed dormancy were detected. The strong seed dormancy of Milyang 23 was linked with three isozyme genes: Pgi‐11 on chromosome 3, Amp‐32 on chromosome 6, and Est‐92 on chromosome 7, while the strong seed dormancy of IR 36 was linked with C+ (apiculus color) on chromosome 6, Est‐92 on Chromosome 7, and Acp‐21 on chromosome 12. The high level of seed dormancy in indicas was found to be due to a cumulative effect of several loci. Differential responses of such loci to a dormancy‐breaking treatment were detected. An allele from IR 36 at a locus on chromosome 6 seemed to be responsible for strong seed dormancy after maturation and to be easily broken during storage. This allele may be incorporated into japonica rices by means of marker C for apiculus color.