Study On Genetic Specialty Of Early Generation Stability And Exploratory Development In Rice Breeding

Early generation stability in rice is a special genetic phenomenon in rice breeding practice. The genetic analysis population had not been built, and SSR molecular marker was only utilized to analyze early stable strains in the previous study on early generation stability in rice. There had not been making tracks for F₁ single plant, F₃ and F₄ population. No comparative study on stable strains and segregating strains had performed in same combination before. So the study on early generation stability was un-systematicness.In our studies, the genetic analysis population was built by utilizing 11 varieties with early generation stability crossing with 7 cultivars. Three types of combinations were obtained, i.e. positive combinations and negative combinations of early generation stability rice crossing each other, early generation stability rice crossing cultivars and cultivars crossing cultivars. By agricultural traits, genetics, SSR and ISSR molecular marker analysis of early generation stability in rice, the studies on recombination and deliver matter of genetic marker in offspring were performed. The genetic differences between stable strains and segregating strains in same combination were studied comparably. The new results, i.e. molecular marker related to early generation stability were obtained. We have suggested genetic mechanism of early generation stability in rice. We have studied how to use the specialty of early generation stability in rice to breed hybrid rice restorer and new hybrid rice. The main results of the studies are as follows:The results of agronomic analysis showed that the frequency of early generation stable strain was 8.96% in F₂ population, of which that of early generation stable rice varieties crossing each other was 28.77%, that of early generation stable rice varieties crossing cultivars was 4.76%. Stable strain did not appear in the combination of cultivars crossing cultivars. We suggested that the parents with early generation stability should be the sponsorship of this special genetic phenomenon, and the factor should exist in early generation stable rice. The frequency of stable strains in positive crossing, 4.96%, was uniform to that of negative crossing, 4.6%. Based on the small difference in frequency and stable strains' appearance in the offspring of both positive cross and negative cross, we suggested that cytoplasmic inheritance should be excluded.The agronomic traits tracking showed the segregating traits among single plants were observed in F₁ population of cross combinations with early generation stable strains, and there were some differences between F₁ single plant breeding stable strains and thatbreeding F2 segregating strains in agronomic trait. Two types of strains existed in F2 population of stable strains: (1) stable strains with uniform agronomic trait; (2) segregating strains that agronomic trait segregated normally. It implied that the Fi single plant of stable strains had been homozygosis genetype plant, and the basic genetic unit of early generation stability was F] single plant or F2 strains.SSR marker showed that Fi single plant, F2 stable strains and F3 stable strain population had uniform molecular marker-bands, all of which was homozygosity marker. Parents' marker bands present. It expressed genetic recombination homozygosity. Fj single plant of segregating strain expressed heterozygosis. The molecular marker of F2 population showed the Mendelian manner law. Homozygosis genetype plant and heterozygosis genetype plant existed in Fi stable strain population of cross combination. The differences between two types of genetypes decided the phenotype differences of F2 population. We suggested the homozygosis genetype should have caused before Fj single plant forming, and homozygosis affair have appeared during hybrid zygote development.Non-parental bands appeared at high frequency in M276, RM258 and RM1 markers loci of stable strains, but non-parental marker bands didn't appear in these loci in single plants of F2 and F3 segregating strains. That the Fi single plant present non-parents bands implied the genetic recombination occurred during Fi zygote development. Based on uniform non-parents bands of Fi stable single plant, F2 stable strains and F3 stable strain population, we had a suggestion that genetic recombination during zygote development should occur only when zygote was heterozygosis genetype. M276, RM258 and RM1 were inkaged with gametophyte gene.We suggested that the early generation stability phenomenon was related to gametophyte gene; some "inducibe factor" should exist in the gamete of stable parents, and this "inducibe factor" might control somatic reduction and cell division mode during zygocyte development process, resulting in somatic reduction happening and forming early generation stable plants.Four types of marker-bands were obtained by marking early generation stable strains in rice by using ISSR markers. Firstly, maternal marker bands present, and paternal marker bands absent; secondly, paternal marker bands present, and maternal marker bands absent; thirdly, parts of maternal and paternal marker bands present, and the others absent; finally, new recombined marker bands appeared, and all maternal and paternal marker bandsabsent. But F2 segregating strains also showed parents' heterzygosity marker bands. It also showed that recombination should happen in forming progress of stable strains.Genetic analysis, SSR marker and ISSR marker implied that the early generation stable strains had been homozygosity in their Fi single plant and its previous period, and gene combination had happened in development of early generation stable strain. So the study direction on early generation stability in rice should transform to cytological study.Wide-compatibility study results of early generation stability rice showed that some varieties had excellent wide-compatibility and broad wide-compatibility spectra, and the others had weak wide-compatibility, and it should be improved when needed.Determining and observing on main effective restoring gene, restorer ability and agronomic traits of stable strains deriving from early generation stable material crossing hybrid rice restorer, the result showed that hybrid rice restorer 2371 with good resistance, excellence of rice quality and good recuperabiljty was screened. Two combinations Zhenxian 97AX2371 and D80AX2371, whose outputs were above 10 per cent higher than that of Shanyou 63, were obtained. It might be a rapid and high efficiency method to breed restorer line in rice.