Sensitivities To Exogenous GA₃in62Accessions, Inheritance Of Flag Leaf Angle And Ssr Marker-assisted Backcrossing In A Cross Of863B/A7444in Japonica Rice （Oryza Sativa L.）

The area planted with hybrid rice occupied60%of the total area of rice in China. It is needed to produce150,000hm2of hybrid seeds each year. In order to improve outcrossing rate, it is nessary to spray GA3and cut partial flag leaf in the process of seed production. However, the spraying of GA3will not only increase cost of seed production, but also pollute environment and make kernel smut heavier. The cutting of flag leaf requires not only a large amount of workers but also high-intensity and high-technique operation. Breeding maintainer lines and restorer lines with high sensitivity to exogenous GA3and large enough flag leaf angle (FLA) are efficient way to solve the problems. So identification of rice germplasms with high sensitivity to exogenous GA3and elucidation genetic mechanism of FLA are basic work to come true the breeding aims above. Therefore, two studies have been conducted in this thesis. First, sensitivities to exogenous GA3of6traits, including plant height (PH), panicle neck length (PNL), flag leaf angle (FLA), length of the1st internode from the top (LFI), length of the2nd internode from the top (LSI) and length of the3rd internode from the top (LTI), were investigated in japonica rice (Oryza sativa L.) by using62accessions. Cluster analyses of the62accessions were carried out based on difference between treatment and control using index of GA3sensitivity (IGS) of PH, PNL and FLA as indicators respectively. Some elite accessions were screened out based on the results of cluster analysis. Second, genetic analysis for FLA was conducted by using mixed major genes plus polygene inheritance models using4generations (P1、P2、F1and F2, in2008) and6generations (P1、P2、F1、B1、B2and F2, in2009) derived from a cross of863B/A7444.863B was a elite japonica maintainer line used widely and with small FLA, and A7444was a landrace of japonica rice in Taihu Lake valley and with large FLA. QTLs for FLA were detected by using composite interval mapping method in the BC1F1population (863B/A7444//863B). Based on SSR markers, six BC1F1plants with high proportion of recurrent parent genome (PRPG) were selected and backcrossed to863B. The results obtained were as follows: 1. Compared with control of spraying water, average values of treatment of all the6traits increased in62accessions. In most accessions, LSI was more sensitivity than that of LFI and LTI. HR-6was clustered into the group of high sensitivity for PH,6427R-2-1for PNL and huangnuoyoumang, nannongjing4004and nannongjing005for FLA.2. The trait of FLA was controlled by two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects when4generations of data in2008were used. Major gene heritability was94.9%and polygene heritability was0.46%. While6generations of data were used in2009, the trait of FLA was controlled by two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance-epistatic effects. Major gene and polygene heritability was91.05%and1.74%in B1generation,22.74%and68.91%in B2generation,90.95%and3.69%in F2generation. Therefore, it can be concluded that FLA was controlled by two major genes plus polygene in the cross of863B/A7444. The two major genes had additive-dominance-epistatic effects. FLA was mainly governed by major genes. The first-parameters showed equivalent additive effect was greater in the first major gene than in the second major gene. The values of additive-by-additive interaction (i) were negative. The values of dominant-by-dominant interaction (l) were positive.3. Four QTL for FLA were detected on chromosome2,3and8in the BC1F1population. qFLA-2x, explained13.64%of phenotypic variation, was located between RM300and RM145on chromosome2. Its positive allele existed in863B and had a additive effect of-27.45. qFLA-3, explained9.32%of phenotypic variation, was located between RM232and RM338on chromosome3. Its positive allele came from A7444and had a additive effect of25.18. qFLA-8-1, with explaining55.24%of phenotypic variation, was located between RM152and RM281on chromosome8. Its positive allele came from A7444and had a additive effect of65.33. qFLA-8-2, with explaining62.37%of phenotypic variation, was located between RM264and RM6215on chromosome8. Its positive allele came from863B and had a additive effect of-66.75. qFLA-8-1and qFLA-8-2were two major genes for controlling FLA.4. Proportion of recurrent parent genome (PRPG) of141plants in BC1F1population ranged from60.9%～86.3%with a mean score of74.9%. Six plants, exhibiting large FLA, high PRPG and similar heading date with recurrent parent, were selected as female parent and backcrossed to863B. The numbers of seed of six BC2F1families obtained were35,76,31,47,40and68, respectively.