Genetic Analysis of Two Weak Dormancy Mutants Derived from Strong Seed Dormancy Wild Type Rice N22 (Oryza sativa)

Two weak dormancy mutants, designated Q4359 and Q4646, were obtained from the rice cultivar N22 after treatment with 400 Gy 60Co gamma-radiation. Compared to the N22 cultivar, the dormancy of the mutant seeds was more readily broken when exposed to a period of room temperature storage. The mutants also showed a reduced level of sensitivity to abscisic acid compared to the N22 cultivar, although Q4359 was more insensitive than Q4646. A genetic analysis indicated that in both mutants, the reduced dormancy trait was caused by a single recessive allele of a nuclear gene, but that the mutated locus was different in each case. The results of quantitative trait locus (QTL) mapping, based on the F-2 population from Q4359 x Nanjing35, suggested that Q4359 lacks the QTL qSdn-1 and carries a novel allele at QTL qSdn-9, while a similar analysis of the Q4646 x Nanjing35 F-2 population suggested that Q4646 lacks QTL qSdn-5, both qSdn-1 and qSdn-5 are major effect seed dormancy QTL in N22. Therefore, these two mutants were helpful to understand the mechanism of seed dormancy in N22.