Genetic Analysis Of Resistance To Sheath Blight And QTL Mapping For Main Characters In Rice

Rice(Oryza sativa L.) is one of the most important crops in the world. Sheath blight resulted from Rhizoctonia solani is the global rice disease. It has already boomed as the most severe disease in many rice growth regions of South China, and severely threatened to rice quality and quantity. Disease-resistant breeding is an effective way to prevent the disease popularity. However, there are very few diseases resistant varieties used in rice production at present, and the most important reason for it is lack of effective resistance sources. Therefore, it is important to carry out genetic studies on rice sheath blight thoroughly and identify markers tightly linked to the resistance genes, and use the markers in disease-resistant breeding.Identification and genetic analysis for sheath blight resistance of4indica rice sources were studied in this thesis. One of these resistance sources, Zhongda304, was used to cross with a susceptive japonica rice, Zhongye1211, to construct recombinant inbred lines (RILs). QTLs mapping were conducted for the sheath blight resistance and13major agronomic characters used SSR molecular markers. And the major agronomic characters of sheath blight resistant RILs were evaluated. The main achievements of the present study were as follows:1. Four indica rice sources with sheath blight resistance, including ZD304, MR1400, T1006and DQ50, were crossed respectively with a highly susceptible japonica rice, ZY1211. Pathogen inoculation evaluation and genetic analysis were conducted for parents and progeny populations. The results indicated that the resistance level of F1populations in the4crosses were between both their parents. The F2populations segregated greatly with continuous unimodal distribution. Results proved that the resistance to sheath blight of the four sources was a quantitative trait, controlled by minor-multiple genes. And their heritabilities were13.4%、48.4%、44.98%and65.66%, respectively.2. The Zhongda304of indica rice with moderately sheath blight resistance was crossed with a susceptive japonica rice, Zhongye1211, to construct RILs of F7populations. The sheath blight resistances of188RILs were evaluated by artificial inoculation with the pathogen by toothpick embedding method. Genetic linkage map for the population was constructed by use of142SSR polymorphic SSR markers distributed uniformly at the12rice chromosomes. The total length of map was1748.8cM with the mean distance between adjacent markers12.32cM. QTLs for the disease resistance were mapped by interval mapping method. Three QTLs, named tentatively as qSB-1, qSB-10and qSB-12, respectively, were found, and they were distributed in the chromosomes1,10and12, respectively. They could explain6.6%,7.2%and5.5%of their phenotypic resistance variances, respectively,and qSB-1is a new loci.3. QTLs mapping of13main agronomic characters, including days to heading, effective tillers per plant, plant height, panicle length, filled grains per panicle, grain number per plant, seed setting rate, grain density, grain length, grain width, grain shape,1000-grain weight, and grain weight per plant in both the early and late seasons, were carried out by interval mapping method with the same RIL population and the same Genetic linkage Map.35QTLs were found in yield component traits in the early season, including4QTLs for days to heading,3for effective tillers per plant,3for grain length,3for filled grains per panicle,2for grains per plant,2for seed setting rate,2for grain density,10for1000-grain weight and6for grain weight per plant.17QTLs were found in traits of grain shape, including3for grain length,11for grain width,3for grain length/width ratio.16QTLs were detected in both two seasons,4.190recombinant inbred lines (RILs) were evaluated for main agronomic characters and sheath blight resistance by artificial inoculation in field,then36RILs with moderately resistance to sheath blight and13RILs not only with moderately sheath blight resistance, but also with excellent agronomic characters were gained,which were valuable materials for rice resistance breeding.The above research achievements set solid base for further fine mapping, cloning and use for marker-assisted selection of the resistant and agronomic characters genes.