Genetic Analysis And Molecular Tagging On A Novel Excessive Tillering Mutant In Rice

Rice is one of the major food sources, which is third to wheat and maize in the world total production of food grains. Tillering in rice (Oryza sativa L.) is an important agronomic trait that determines grain production, and it is pointed out that tiller number should be moderate in super-rice. As a special kind of branch of monocotyledonous plants, rice tillering is also of developmental importance. Therefore, tillering of rice is one of the focuses in rice genetic and developmental research.A rice mutant with an excessive tiller number, designated ext-M1B, was found in the F2 progenies generated from the cross of M1B and GMS-1(a genetic male sterile), whose number of tillers was 121. The excessive tillering mutant ext-M1B also resulted in significant changes in height of plant, flag leaf, stem, filled grains per panicle, productive panicles per plant—the plant height shortened about three quarters; the leaves were short and narrow remarkably; the productive panicles per plant increased; the filled grains per panicle became reduced.The inbreeding progenies of ext-M1B showed the same mutant phenotype. The crosses from ext-M1B / M1B, M1B/ ext-M1B, 2480B / ext-M1B, D62B / ext-M1B, G46B / ext-M1B and G683B / ext-M1B expressed normal tillering in F1, and segregated into the two different phenotypes, normal tillering type and excessive tillering type in the ratio of 3:1 in F2. At the same time, it was found that the phenotypes of excessive tillering and normal tillering plants in F2 populations were similar to that of ext-M1B and another corresponding parents with normal tillering respectively, and there was no tall individual in the excessive tillering plants and no dwarf individual in the normal tillering plants. These results indicated that the excessive tillering trait of ext-M1B is controlled by one recessive nuclear gene.The F2 population of 2480B / ext-M1B was used as the mapping population of the mutant gene. It consisted of 602 recessive excessive tillering individual plants and 1865 homologous dominant normal tiller number individual plants. The genomic DNA of parents, 2480B and ext-M1B, were amplified with 520 pairs of primers of microsatellite markers well-distributed on 12 chromosomes in rice. The results indicated that the ratio of parental polymorphism is 8.89%. The genomic DNA of F2 recessive individuals wasamplified with the parental polymorphism of microsatellite markers. The results suggested that there is a linkage relationship between RM584, RM225, RM197 and the target gene.The linkage map of the excessive tillering mutant gene was constructed with the segregation data of the plant tillering and microsatellite markers of the F2 mapping population of 2480B / ext-M1B. The results indicated that the excessive tillering gene was located on the side of the microsatellite markers, RM197, RM548, and RM225, on the short arm of rice chromosome 6 near centromere region, and the genetic distance from the target gene to the markers, RM197, RM584, and RM225, was 3.8cM, 5.1 cM, and 5.2 cM, respectively. This gene, probably being a new excessive tillering gene in rice, is designated tentatively as ext-M1B (t).